General Science Grade 7 Student Textbook PDF

General Science Student Textbook Grade 7 Authors Hassen Worku (PhD) Awoke Debebe (MSc) Seid Mohammed Shfaw (MSc) Muluneh Workie (MSc) Editors Getachew Tarekegn (PhD) Kindu Nibret (MSc)...

General Science Student Textbook Grade 7 Authors Hassen Worku (PhD) Awoke Debebe (MSc) Seid Mohammed Shfaw (MSc) Muluneh Workie (MSc) Editors Getachew Tarekegn (PhD) Kindu Nibret (MSc) Agmas Amare (MSc) Team Leader Ehtegebreal Aregehagn (MEd) Illustrator Belayhun Tsegaye Designer Atersaw Tigyhun (MSc) Amhara National Regional State Education Bureau The textbook is prepared by Amhara National Regional State Education Bureau and the Scholars Council with budget allocated by the Amhara National Regional State Government. ©2015 Amhara National Regional State Education Bureau. All rights reserved. Scholars Council Amhara National Regional State Education Bureau  Table of Contents Introduction..........................................................................................................v Unit 1 Basic Concepts of Science 1.1 Nature of science............................................................................................1 1.2 Scientific measurement..................................................................................12 1.3 Common laboratory equipment, uses, safety rules and procedures in science laboratories.................................................................................................20 Unit 2 Matter in Our Surroundings 2.1. Characteristics and nature of matter.............................................................31 2.2 Physical and chemical properties of matter...................................................38 2.3. Classification of substances with composition and observable properties...40 2.4 Changes around us: Physical and chemical change.......................................46 2.5 Separation of mixtures and its application.....................................................50 Unit 3 Elements,Compounds and Chemical Reactions 3.1. Elements and their representation................................................................66 3.2. Compounds and their representation............................................................69 3.3 Simple chemical reactions and equations......................................................81 3.4 Uses of chemical reactions in everyday situation..........................................92 Unit 4 Cell as the Basis of Life 4.1 Microscope.....................................................................................................97 4.2 Cell.................................................................................................................106 Unit 5 Living Things and their Diversity 5.1 Living things..................................................................................................126 5.2 Kingdoms of living things............................................................................132 General Science Grade 7 Student’s textbook iii  Unit 6 The Earth 6.1 Shape and dimensions of earth......................................................................158 6.2 Parts of the earth...........................................................................................160 6.3 Movements of the earth.................................................................................161 6.4 Earth’s subsystems........................................................................................163 6.5 Carbon and water cycles................................................................................165 Unit 7 Force, Motion and Energy 7.1 Definition of motion.......................................................................................172 7.2 Types of motion.............................................................................................174 7.3 Motion in straight line....................................................................................175 7.4 Force..............................................................................................................182 7.4.2 Force of gravity...........................................................................................184 7.5 Force and motion...........................................................................................186 7.6 Energy............................................................................................................191 iv General Science Grade 7 Student’s textbook  Introduction Rationale for the Curriculum Reform Different studies have been conducted to improve the relevance and quality of Ethiopian general education. Worth mentioning are the Education Road-map (2018) and Cambridge Assessment Studies (2019). On top of these, the Ministry of Education and Amhara National Regional State Education Bureau carried out repeated monitoring and assessment of the school curriculum. The study and assessment reports consistently reiterated that the previous general education curriculum had weaknesses. Some of the weaknesses were: The curriculum focused on low-level cognitive domain of learning; the presentation of some contents in the curriculum did not consider students’ age and maturity level, and the curriculum did not acknowledge indigenous knowledge systems. Furthermore, the curriculum did not adequately encourage students to develop scientific thinking skills such as observing, classifying, inferring, measuring, communicating, predicting, identifying variables, constructing hypotheses, tabulating and graphing data, defining variables, designing investigations, and experimenting. It also did not provide adequate opportunity for students to develop 21st-century skills such as critical thinking, problem-solving, global and cultural awareness, digital literacy, oral and written communication, creativity, collaboration, decision making, and the like. To alleviate these shortcomings, a new curriculum framework and syllabus have been developed. General science textbooks are developed on the bases of the new curriculum framework and grades 7 and 8 general science syllabus. General science curriculum Based on the new curriculum framework, general science textbooks are prepared for middle school students (grades 7 and 8). General Science education includes physics, chemistry, and biology subjects. General Science education aims to equip students with foundational science knowledge and skill that serve as a base for secondary education. It intends to nurture scientific inquiry skills which students use on their day to day lives and in learning science. In addition, it aims to cultivate among students science processes and 21st-century skills that can be used in their day-to-day life and academic career. General Science Grade 7 Student’s textbook v To achieve these major goals of general science education, the textbooks are prepared based on the principles of inquiry-based, problem-based and context- based learning. Inquiry is the intentional process of identifying problems, critiquing experiments, distinguishing alternatives, planning investigations, researching conjectures, searching for information, constructing models, debating with peers, and forming coherent arguments. Inquiry-based learning involves posing questions, making observations, reading books to find out what others have learned, planning investigations, gathering, and analyzing information, reflecting on what was learned in the light of new evidence, and proposing explanations and predictions. It encourages students to use critical thinking skills that include designing and carrying out investigations, interpreting data as evidence, creating arguments, building models, and communicating findings to deepen students understanding through logic and evidence. Problem-based learning allows students to become the drivers of their learning. Problem-based learning uses complex, real-world issues as the classroom’s subject matter, encourage students to develop problem-solving skills and learn concepts instead of just absorbing facts. It promotes students’ conceptual learning and skill development. It helps students to acquire knowledge and skill in the context of real-world problems. It engages the students in solving meaningful problems. Context-based learning is using students’ prior knowledge, experience, and context as a base for the new knowledge and skill development. It encourages students to recall, relate, describe, or apply knowledge from relevant prior experience that can be used as a foundation for the new knowledge. Teachers, students, and parents will take part in the knowledge construction process. It is important that teachers, students, and parents engage in observations, experiments, and construction of knowledge. Hence, the textbooks are intended not only to provide adequate knowledge and skill but also develop among students learning to learn skills. vi General Science Grade 7 Student’s textbook  Implementation of the new learning and teaching techniques and methods General science textbooks include many activities that are helpful to put into practice the aforementioned learning-teaching methods. The activities are designed based on students’ prior knowledge, skill, and experiences. They are aimed to connect students’ life experience with classroom science, to develop students’ science process, inquiry, and 21st-century skills. To achieve the aims of these activities, students should prepare themselves before class, and should be active participants in the classroom. Teachers should encourage students to work on the activities before class. During the teaching-learning process, the teachers are not expected to provide answers for each activity before the students work on it. The students should be given enough time, needed materials, and clues while they are working on the activities. The teachers should lead students’ work very closely and scaffold them when necessary. Contents in the textbooks require appropriate utilization of instructional time and extending learning to home and libraries. It is also indispensable that every student brings his or her textbook to class. Parents should also assist students in carrying out different activities. It is critical that teachers ensure that all activities and contents in textbooks are properly covered and learned by students. Dear students, please take good care of the textbook! Learning requires effort, experimenting, and exercise! We wish you a successful academic year General Science Grade 7 Student’s textbook vii  Unit 1 : Basic Concepts of Science Unit Basic Concepts of 1 Science Learning outcomes: At the end of this unit, you will be able to:  Explain the nature of science.  Describe the main branches of science.  Explain the difference between science and technology.  Explain how science and technology affects human behavior, practice and ways of thinking.  Appreciate the contributions of famous Ethiopian scientists to science and technology.  Identify basic and derived units of measurements.  Explain the concept of measuring physical quantities.  Explain the difference between scalar, vector physical quantities, fundamental and derived physical quantities.  Identify different laboratory tools.  Demonstrate safe ways of using apparatus in the laboratory.  Practice precautionary measures in the laboratory.  Apply laboratory safety rules and procedures.  Identify potential hazards when doing laboratory Experiment s. 1.1 Nature of science 1.1.1 Definition of science In order to understand what science is, it is necessary to deal with the key characteristics of science. Discuss Activity 1.1 in groups and reflect your positions to your teacher. General Science Grade 7 Student’s textbook 1  Unit 1 : Basic Concepts of Science Activity 1.1 The following statements describe some aspects of science and scientific knowledge. Discuss in groups whether you agree or disagree with the statements. 1. Scientific knowledge is absolute and unchanging. 2. Science always involves Experiment s. 3. There is single scientific method that all scientists follow. 4. Scientific theory and scientific law represent the same concept. Activity 1.2 Consider a cube placed at the center of a Table as shown in the picture and answer the questions below. (Note that when you are working in a group, do not turn, lift or open the cube to see what is on the bottom). 1. What do you observe on the Table ? 2. Based on your observation, A. What number is on the bottom of the cube? B. What is the color of the bottom face? C. What is the pattern of the bottom face? (Justify your answers based on your observations) When doing Activity 1.2, you demonstrated some characteristics of the nature of science and you did in a similar manner as scientists do. For example you:  Worked in group  Observed the cube  Inferred answers based on your observation and experience  Supported your answers (inferences) with evidence from your observation. You also used your creativity and imagination to determine patterns and relationships. Scientists make inferences in a similar way as you did when they attempt to find answers to questions about natural phenomena. 2 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science In your discussion, you probably came up with different answers to the questions. The existence of different answers to the same question based on the same evidence is another characteristic of the nature of science. In the same manner, scientists can come up with different ideas based on the same set of data. In general, the characteristics of the Nature of Science (NOS) and their respective descriptions are given in Table 1.1 below. Table 1.1 Characteristics of nature of science Characteristics of Nature of Description Science Empirical evidence in the form of quantitative Scientific knowledge is based on and qualitative data is the base of scientific empirical evidence. knowledge. Scientific knowledge should not be viewed as Scientific knowledge is tentative. absolute. It can be changed with the existence of new evidence. Scientific knowledge is the Scientific knowledge is developed from a product of observation and combination of observations and inferences. inference. Scientific knowledge is the Scientists often use creative methods and product of creative thinking. procedures throughout their investigations. A scientific law is a description of relationship Scientific laws and theories or pattern based on observations. Scientific are different kinds of scientific theories are a well-supported explanations for knowledge. scientific phenomena. Scientists use many methods to There is no a single “scientific method” used develop scientific knowledge. by all scientists. Science is a result of social or collaborative Science is a social Activity that effort and personal background or experience possesses inherent subjectivity. affects our observations. Therefore, science is not only a body of knowledge. It is also described as a way of knowing the natural world through investigating observation and evidence using creative and imaginative ways. General Science Grade 7 Student’s textbook 3  Unit 1 : Basic Concepts of Science Activity 1.3 Read individually the following text about telephone invention and identify the statements which describe the characteristics of the nature of science. Match the identified statements with the different characteristics of the nature of science. Brief history of telephone invention Telephone is one of the most important inventions. It lets people talk to each other at the same time across long distances. It is one of the greatest inventions in communication technology. The invention changed the way we communicate today. Many inventors were working on electronic voice transmission during the time of the invention of telephone. However, Alexander Graham Bell was the first to be awarded a patent for the electric telephone in 1876. He developed new and original ideas by building on older ideas and developments. He drew his inspiration from teaching deaf and observation of his hearing-impaired mom. His endless scientific curiosity, creativity and understanding of sound and electricity led him to invent the telephone. His invention has become a base for today’s wireless telephones. 1.1.2 Branches of science Science can be divided into three major branches. These branches are life science, physical science and earth science. While life science studies living things, physical science studies about non-living things. Earth science is concerned with the study of earth’s structure, properties, and processes. 4 General Science Grade 7 Student’s textbook Unit 1 : Basic Concepts of Science Science Life Science Physical Science Earth Science Biology Physics Chemistry Figure 1.1 Branches of science 1.1.3 Conventional and indigenous knowledge Activity 1.4 Imagine that you are caught with a common cold in a place where there is no health institution such as clinic, hospital, and pharmacy. What do you do to get rid of the disease? Activity 1.5 Read the following scenario and discuss the questions below. The scenario is about a girl and a boy who were caught with malaria, and what they did to be cured from it. Scenario The girl went to a hospital to get her doctor immediately after she recognized some symptoms of malaria. The doctor diagnosed her and found malaria from her blood test. The doctor then gave her some medicines. After she had taken the medicines, she recovered from the disease. On the other hand, the boy went to an old man’s house when he felt a headache. The old man lived near the boy’s house and was experienced in traditional medicine. When the boy arrived, the old man asked him some questions in relation to his headache. After the old man listened to the boy carefully, he went to a garden and came with some leaves. He squeezed the leaves with water into a beaker and gave it to the boy. The boy then drank the traditional medicine. After some time, the boy got relief from his headache. General Science Grade 7 Student’s textbook 5  Unit 1 : Basic Concepts of Science Questions 1. If you were the person who had been caught with malaria, where would you go to recover from your illness? To the hospital or to the old man? Justify your choice. Indigenous knowledge and conventional knowledge represent two knowledge categories. They are obtained by different ways of looking at the world around us. Conventional knowledge is acquired through the method of conventional science. Terms such as “modern knowledge” and “western knowledge” are often used to refer to conventional knowledge. This type of knowledge system has the following characteristics.  It is tentative  It is evidence supported  It is based on observation and inferences  It is systematically documented  It is learned by formal education. Indigenous knowledge is a knowledge system built up by a group of people in a given culture. It is obtained through the accumulation of experiences, informal education and intimate understanding of their environment. Indigenous knowledge is also called “traditional knowledge”, “local knowledge” or “native knowledge”. This knowledge system has the following characteristics  It is based on experience and acquired from observations over time  It is unwritten and known through oral traditions  It is embedded in culture  It is unique to a given society  It is subjective and long term wisdom. In our surrounding there are many examples of indigenous knowledge. Some of them are the following.  Traditional medicine  Traditional alcohol production  Drying (for food preservation)  Traditional weaving 6 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science  Tracing and crop rotation (for soil conservation)  Traditional water conservations Project work It is known that Ethiopia is very rich in different indigenous knowledge. By asking your parents, write as many types of indigenous knowledge as you can and report to your teacher. Your report should contain the local names of the indigenous knowledge and their benefits and weaknesses, if they have. 1.1.4 Science and technology Activity 1.6 1. How are science and technology related? How are they different? 2. What do you think are the effects of science and technology? 3. Which has a more direct effect on society? Science or technology? Justify your answers. The relation between science and technology are reciprocal. A scientific explanation of a phenomenon leads to a technological development that serves a societal need. Conversely, a societal need results in a technological solution, which then leads to a scientific explanation. However, technology often has a more direct effect on society as it solves practical problems and serves human needs. Science and technology have some differences as shown in the following Table 1.2. General Science Grade 7 Student’s textbook 7  Unit 1 : Basic Concepts of Science Table 1.2: Difference between science and technology Science Technology  It is the process of exploring  It is the practical application of new knowledge. scientific knowledge.  It is always useful.  It can be useful or harmful.  It emphasizes discovery.  It emphasizes invention.  It is used to make  Technology simplifies human life. predictions.  It advances scientific  It advances the standard of living knowledge and discovery. in societies. Activity 1.7 Read the following two paragraphs and discuss the questions below. History of light bulb More than 150 years ago, inventors began working on a bright idea. The idea was to invent the light bulb. Like all other great inventions, the light bulb can’t be credited to one inventor. It was a series of small improvements on the ideas of previous inventors. This led to the idea and the invention of light bulbs we use in our homes today. It was Thomas Edison who discovered the light bulb in 1879. Thomas Edison did not stop his contribution to improve electric lighting after the invention. He was working to improve the bulb that made the use of light bulbs practical. 8 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science Questions 1. Is the development scientific or technological? Which statement in the paragraphs supports your answer? 2. What benefits did scientific and technological development provide to society? Activity 1.8 Do the following questions at your home and present your answers to your classmates. 1. List some examples of technologies that are used by the community in your surrounding and discuss how these technologies solve practical problems of the community. 2. Do these technologies have risks? If they have, what are their risks? 1.1.5 Scientists and ethical discipline Since science is a human Activity , it relates to different human values. The diverse set of values that contribute to the regulation of scientific activities is said to be scientific ethics or scientific discipline. Scientific ethics is extremely integrated into the ways scientists do their work. Thus, the reliability of their work and the scientific knowledge they investigated depends upon whether they follow the ethic or not. Some of the ethical disciplines in science are the following. 1. Integrity and honesty in reporting scientific data. 2. Careful analysis of scientific results to avoid error. 3. Proper crediting of sources of information, data, and ideas 4. Objective interpretation of results without bias. 5. Informing members of the community about any risks of the scientific investigation. 1.1.6 Ethiopian scientists There are many scientists around the world who contributed to the development of science and technology. The following are some of the Ethiopian scientists who played a big role in technological advancement. General Science Grade 7 Student’s textbook 9  Unit 1 : Basic Concepts of Science Ethiopian Scientist Major contributions  Inventing two aerospace mechanisms which were patented under National Aeronautics and Space Administration’s (NASA) new technology.  Creating space shuttles and rockets that assisted in planetary science.  Innovative creations of the Global Positioning System Dr. Kitaw Ejigu (GPS), and a revolutionary and dynamic flight simulator for the Boeing Company.  Outstanding research in ceramic science  Developed new ways of using solar energy to make fuels like hydrogen and methane.  Investigated solid electrolytes Dr. Sossina Haile  Investigated ‘sorghum’ with high nutritional quality; Which tolerates drought and cold and Which has resistance to pests, diseases and the parasitic weed. Professor Gebisa Ejeta 10 General Science Grade 7 Student’s textbook Unit 1 : Basic Concepts of Science  Co-founder of Mechanism Design for Social Good, to improve access to opportunity for historically disadvantaged communities.  Co-founder for Black in AI (Artificial Intelligence)- A place for sharing ideas, fostering collaboration and Dr. Rediet Abebe discussing initiatives to increases black people in the field of artificial intelligence.  Discovered medicine to prevent the parasitic disease, ‘Bilharzia’, from the fruit of a common African plant, the “Endod” Dr. Aklilu Lemma  A respected scientist in human physiology  Assessing the medical and nutritional value of plants.  Examining the health hazards of medical plants to humans, animals and the environment Professor Alemtsehay Mekonnon Activity 1. 9 1. Take one Ethiopian scientist, write a short biography of him/her and briefly describe the contributions of his/her work to the society. General Science Grade 7 Student’s textbook 11  Unit 1 : Basic Concepts of Science 1.2 Scientific measurement Measurable quantities which are used to describe physical phenomena are called physical quantities. Length, mass, time, volume, density and temperature are some examples of physical quantities. Physical quantities possess at least magnitude (numerical value) and unit. 1.2.1 Fundamental and derived physical quantities Physical quantities can be divided into two. These are fundamental (basic) quantities and derived quantities. Fundamental physical quantities are quantities which can be measured directly. They are not described in terms of other physical quantities. Length, mass, time, temperature, electric current, amount of substances and luminous intensity are the seven fundamental physical quantities. The units used to measure these fundamental quantities are called fundamental units. The seven fundamental quantities with their respective SI units are shown in Table 1.3. Table 1.3 Fundamental physical quantities and fundamental units Basic Quantities Basic Units Name Symbol Name Symbol Length l meter m Time t second s Mass m kilogram kg Temperature T Kelvin K Current I Ampere A Amount of substance N mole mol Luminous intensity Candela Cd Derived physical quantities are quantities that can be obtained by the combination of the fundamental quantities. Area, density, speed and volume are examples of derived physical quantities. All derived physical quantities have derived units. Table 1.4 presents some examples of derived physical quantities and their respective units. 12 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science Table 1.4 Some examples of derived physical quantities and derived units Derived Quantities Derived Units Name Formula Name Symbol Velocity Distance/Time Meter per second m/s Acceleration Velocity/Time Meter per second squared m/s2 Force (Mass) (Acceleration) Newton kg.m/s2 Work (Force)(Distance) Joule kg.m2/s2 Activity 1. 10 Express the derived units of the following quantities in terms of the fundamental units.  Area  Volume  Density  Power 1.2.2 Scalar and vector physical quantities Some physical quantities are described completely by only a number and a unit (magnitude). This type of quantities is called scalar physical quantities. Scalar quantities do not require direction for their description. Time, mass, volume, density, temperature and energy are examples of scalar quantities. However, there are quantities that cannot be described fully by the use of only magnitude. To describe these quantities, both magnitude and direction are required. Quantities which have both magnitude and direction are called vector physical quantities. Displacement, velocity and force are examples of vector quantities. Prefixes We commonly write numbers using scientific notations. Scientific notation is the short hand representations of very large or very small numbers. For example, 1000g can be written as 1×103 g. But, it is possible to replace the 103 with the prefix called “k” (kilo). Therefore, 1×103 g can be written as 1kg. Table 1.5 presents prefixes, their symbols and values. General Science Grade 7 Student’s textbook 13  Unit 1 : Basic Concepts of Science Table 1. 5 Prefixes Prefix Symbol Value Prefix Symbol Value peta P 1015 femto f 10-15 tera T 1012 pico p 10-12 giga G 109 nano n 10-9 mega M 106 micro µ 10-6 kilo k 103 milli m 10-3 hecto h 102 centi c 10-2 deka da 101 deci d 10-1 1.2.3 Measuring physical quantities Measurement is a way of describing the natural world with numbers. Measuring something means comparing the quantity to be measured with a reference standard unit. Standard unit of measurements are unit of measurements which are well- defined, highly precise and easily reproducible. They are unchanging with respect to place, time and physical conditions. These standard units are known as System of International Units (SI units). For example, ‘second’ is a standard unit of measuring time. So, the duration of a second is fixed and the same to everyone at every place on earth. Measuring Length Length is a fundamental physical quantity that represents distance between two points. Length is often designated by “l”. But, it can also be designated by symbols such as ‘b’, ‘h’, ‘w’ etc. The SI unit of length is meter (m). The non-SI units of length are centimeter (cm), millimeter (mm), kilometer (km), etc. Length can be measured in two ways: traditionally and scientifically. Traditionally, length can be measured by units such as ‘hand span’, ‘cubit’, ‘foot’ and ‘yard’. However, these traditional units are not reliable. This is because measurements using these units vary from person to person. On the other hand, the scientific way of measuring length used scientific instruments such as ruler, Vernier caliper, and micrometer to measure length. In scientific way, standard units of measurement are used to measure length. 14 General Science Grade 7 Student’s textbook Unit 1 : Basic Concepts of Science Figure 1.1: Length measuring instruments Activity 1. 11 Form a group and do the following activities. 1. Measure the lengths of the following objects using appropriate traditional ways and write the measurements in the Table. 2. Measure the length of the objects using appropriate scientific instruments and write the measurements in the Table. (Note: Take the measurements of the length of each objects by three different students) Measurements Objects to be measured Traditional Scientific S1 S2 S3 S1 S2 S3 A. Width of the blackboard B. Thickness of your General Science textbook C. Length of your Table Questions A. Which set of measurements (traditional or scientific) is more reliable? Why? B. Are the scientific measurements of the three students equal? If not, why? General Science Grade 7 Student’s textbook 15  Unit 1 : Basic Concepts of Science The length of an object to be measured determines the type of unit to be used. For example, centimeter (cm) and millimeter (mm) are appropriate to measure small lengths whereas kilometer (km) is suiTable for measuring longer lengths. So, we can use meter to measure the width of the classroom, kilometer to measure the distance from Bahir Dar to Gondar, millimeter to measure the thickness of an electric wire, and so on. Measuring Mass Activity 1. 12 1. Explain how we measure mass traditionally? Share your experiences with your peers. 2. How do you measure mass of jewelries? What is the appropriate unit to measure mass of jewelries? Mass is a fundamental physical quantity that describes the amount of matter contained in a body. It is symbolized by ‘m’. The SI unit of mass is kilogram (kg). The non-SI units of mass are Gram (g), milligram (mg), quintal, ton and so on. Smaller masses are measured using grams and kilogram while larger masses are measured using quintals and tons. Mass can be measured both traditionally and scientifically. Traditionally, instruments such as ‘kuna’, ‘tassa’ and traditional beam balance are used to measure mass. Where as to measure mass scientifically, we use scientific instruments such as beam balance. A common type of beam balance consists of a uniform beam having two pans. To measure mass of a body, a known standard (for example 1kg) is placed on one pan, and the body to be measured is placed on the other pan. The unknown mass of the body will be equal to the known standard when the beam balance is balanced. Figure 1.2 shows different mass measuring instruments. Figure 1.2 Mass measuring instruments 16 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science Activity 1. 13 Form a group and do the following activities. 1. How do we measure small masses such as a single grain or a single Teff? 2. Estimate and then measure the mass of the following objects and write your estimation and measurement on the space provided. Compare the estimated value with the measured value. Objects to measured Estimated Value Measured Value A. Your General Science textbook B. One stick chalk C. A duster Measuring Time Activity 1. 14 1. Put your hand on your neck and count 50, 100 and 150 heartbeats. 2. Measure the time you need to count 50, 100 and 150 heartbeats. 3. Tell to your classmates and teacher how you measured the time. Time is a fundamental physical quantity that describes the duration between the beginning and end of an event. It is designated by ‘t’. The SI unit of time is second (s). The non-SI units of time are Year, month, day, hour, and minutes. Similar to length and mass, time is measured using traditional and scientific ways. Traditionally, people used methods such as shadow, position of sun, cook crows and bird’s crisps to estimate time. For example, bird’s crisps indicate the dawning of the day. On the other hand, the scientific way of measuring time involves the use of clocks and watches to measure time. Figure 1.3 shows some time measuring watches. General Science Grade 7 Student’s textbook 17  Unit 1 : Basic Concepts of Science Figure 1.3 Time measuring devices Activity 1. 15 Make your own sundial. Materials required: hoe, wooden stick, marking rocks or cards 1. Find a location, that remains sunny, in your school compound. 2. Dig a hole and place a wooden stick on the hole. Make sure that the wooden hole stays upright. 3. Mark the shadow of the wooden stick every hour using a rock or a card. 4. Write the number for the hour (such as 4 ) on the rock or card. 5. Do you observe that the angle between consecutive cards or rocks is the same or different? Justify your answer. 6. How is your sundial similar or different from a clock? 18 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science 1.2.4 Accuracy and precision in measurements Activity 1. 16 Assume that four groups of students measured the boling temperature of water. Their measurements are recorded in the following Table. Based on the data in the Table , answer the following questions. 1. Which group has measured an average boiling temperature closest to the expected value? 2. Which group measurements are close to each other? 3. One of the students in group A was not happy with the group’s result. Why do you think this was? 4. Suggest two reasons why group A’s results are different to the rest of the class. Boiling temperature of water ( o C) (100o) Trials Group A Group B Group C Group D 1 90.0 95.0 99.0 102.5 2 91.0 100.0 100.0 100.0 3 90.5 101.0 99.5 101.0 Mean 90.5 Accuracy and precision are two concepts which are related to measurement. Accuracy refers to how close a measurement is to its actual or expected value. For example, in the above Activity , the average of measurements of group C is more accurate that of the other groups. This is because the average value of measurements in group C is close to the actual value (100oC). Precision refers to the consistency of two or more measurements namely how close these measurements are to each other. For example, in the above Activity, the measurements recorded by group A are precise than the others. This is because the measurements in group A are more close to each other than the measurements in the other groups. General Science Grade 7 Student’s textbook 19  Unit 1 : Basic Concepts of Science 1.3 Common laboratory equipment, uses, safety rules and procedures in science laboratories 1.3.1 Laboratory safety rules Activity 1. 17 1.When cooking, what safety precautions should be taken? (To avoid burns, cuts, etc.) 2. When doing science Experiment s, what similar kinds and other safety precautions should be taken? 3. To what extent is your classroom or school prepared for a kind of emergency you might have when doing science Experiment s? 4. Is there any safety equipment in your school? Look around your classroom or school for any safety related equipment. 5. Draw a floor plan of the room or building and clearly label where each item is located. Discuss with your friend or classmate? 6. Why is it important to know where safety equipment is located? Laboratory safety involves good laboratory practice by establishing a safe environment. Laboratories can be hazardous if the rules are not followed. In a laboratory Activity , a student may handle materials which are hazardous, poisonous, flammable, and explosive. Some of these materials and equipment may also cause severe burns or cuts if they are handled improperly or carelessly. Most accidents that occur in the laboratory are a result of carelessness, impatience, improper or unauthorized Experiment ation, and disregard for safety rules or proper operating procedures. To minimize the chances of an accident in the laboratory certain rules and regulations must be obeyed at all times when one is working or observing in a laboratory. Therefore, it is not advisable for anyone to work in a laboratory without proper knowledge of the dangers involved.. The followings are some of the basic safety rules to avoid hazards and accidents during laboratory activities. 20 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science 1. DO NOT perform unauthorized Experiment s or work in a laboratory alone. 2. If you get a chemical in your eye, rinse immediately with large quantities of water. 3. Long hair and loose clothing must be confined while in a laboratory. 4. Appropriate clothing must be worn at all times while in the laboratory. 5. Eating and drinking are not allowed in a laboratory. 6. Never direct the open end of the test tube toward yourself or anyone else. 7. Never pour water into concentrated acid. 8. Liquid and solid waste containers must be properly used at all times. 9. Report any accident and/or injury, however minor, to your teacher immediately. 10. Clean up any spill immediately. 1.3.2 Hazard signs (symbols) and some personal protective equipment in the laboratory There is always a possibility of hazard or accidents in laboratories. Hazard signs are put on the bottles or containers of some chemicals. So we should understand the hazards associated with these chemicals and take extra care. There is also a possibility of fire hazard and electrical hazard in the laboratory. Hazard signs are also put on the walls at different places in the laboratory. It is important that you are aware of the potential hazards and risks in the laborato- ry. It is vital that you and the whole class understand each hazard of the laboratory and take the necessary care. This can save us from different accidents that can happen in the laboratory. General Science Grade 7 Student’s textbook 21  Unit 1 : Basic Concepts of Science Activity 1.18 Look at the following laboratory hazard signs. Then match the signs with the meanings of the signs listed below. A. Corrosive material F. Harmful irritant B. No open flames G. Poison/ toxic material C. Electrical hazard H. Flammable gas D. Oxidizing agent I. Explosive hazard E. Flammable and combustible J. High voltage 1 2 3 4 5 6 7 8 9 10 Figure 1.4 Symbols of hazard signs 1.3.3 Personal protective equipment in the laboratory activity Science Experiment s often can lead to an unexpected hazardous situation. Wearing personal protective equipment (PPE) is an easy choice that can save you from grief. The purpose of PPE is to protect individuals from hazards during a specific task. PPE should be selected based on a hazard assessment of the specific task. When you are around hazardous chemicals or equipment (even if you are not using them), a minimum level of PPE should be applied. PPE minimizes the chance of harm from the hazard but does not alter the nature of the hazard itself. 22 General Science Grade 7 Student’s textbook Unit 1 : Basic Concepts of Science Activity 1.19 Look at the following laboratory personal protective equipment and match images with names. 1. Safety glass 2. Fire extinguisher 3. Glove 4. Face shield Figure 1.5 Laboratory personal protective equipment 1.3.4 Common laboratory equipment/tools Activity 1. 20 Look at the pictures of laboratory equipment/ tools in the Table below and match their names with their functions. 1. Used to hold multiple test tubes upright at the same time. 2. Used for holding small samples or for covering beakers or evaporating dishes. 3. Used to determine the mass of chemicals. 4. Used for funneling liquids from one container to another or for filtering when equipped with filter paper. 5. Useful as a reaction container or to hold liquid or solid samples. They are also used to catch liquids from titration and filtrates from filtering operations. 6. Are sources of heat. 7. Used for addition of liquids drop by drop General Science Grade 7 Student’s textbook 23  Unit 1 : Basic Concepts of Science 8. Used to mix, heat and/or hold small quantities of chemicals for assays and laboratory Experiment s 9. Used for holding items 10. Used on a ring supports beakers to be heated by Bunsen burners 11. Used for holding test tubes when tubes should not be touched 12. Used to examine too small objects such as cells, microorganisms, etc. that cannot be seen by the naked eye. 13. Used to produce a magnified image of an object. Equipment/ tool Figure 1.6 Common laboratory equipment Activity 1.21 Assume that you are doing an evaporation Experiment to get the salt that has dissolved in water. 1. What kinds of laboratory equipment do you need? Why? 2. What are the possible hazards associated with this Experiment ? 3. What safety measures will you follow? 24 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science 1.3.5 Making laboratory equipment/tools from locally available materials For junior schools, we do not need a great deal of expensive laboratory apparatus to perform Experiment s. We can make much of the equipment from ordinary things in our home or surrounding. In this section, you are going to make some laboratory tools from local materials. Project work Activity 1.22 Prepare the following laboratory tools from local materials in groups. Use the pictures given above to help you imagine the design. If you need help, contact your teacher. Your teacher will assign one laboratory tool for each group. 1.Test tube holder 3. Test tube rack 5. Wire gauze 2. Alcohol burner 4. Beaker 6. Funnel General Science Grade 7 Student’s textbook 25  Unit 1 : Basic Concepts of Science Summary  Science can be defined as a way of knowing the natural world through investigating evidence together and making sense of that evidence to explain the natural world.  Science has three major branches: Life science, physical science and earth science. Life science studies living things.  Conventional knowledge is acquired through the method of conventional science and characterized by tentativeness, evidence supported, claims based on observation and inferences, systematically documented, and learned by formal education.  Indigenous knowledge is a knowledge system built up by a group of people through the accumulation of experiences, informal Experiment s and intimate understanding of the environment in a given culture.  Technology refers to the process of applying scientific knowledge in practical applications for various purposes.  Technology has a more direct effect on society as it solves practical problems and serves human needs.  Adhering to safety rules is important while working in the laboratory.  Measurement of an object consists of units and numerical values. Traditional units of measurements are not reliable and not exact but the conventional (SI) units are more reliable.  Physical quantities can be basic, derived, scalar or vector quantities.  Fundamental quantities are quantities that are obtained by direct measurement, but derived quantities are obtained by combining the fundamental quantities.  Quantities that can be described by only magnitude are called scalar quantities.  Quantities that can be described by both magnitude and direction are called vector quantities. 26 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science Review questions and problems I. Choose the best answer from the given alternatives 1.At one time, many people thought disease was caused by fate or misbehavior. Following the invention of the microscope, bacteria were discovered. After this, a new theory of what causes disease arose that was known as the germ theory. Why was the original theory modified? A. It quickly became obvious that germs causes disease B. The person who invented the microscope became ill C. New evidence promoted revision to the original ideas D. The proponents of the germ theory had political power 2. Which of the following is true about theory and law? A. A theory explains a set of well tested observations; and a law describes a pattern in nature B. Law can be changed with the addition of new evidence but theories can not C. A law explains pattern in nature in more detail than a theory D. Theory and law can be used interchangeably 3. Why is it necessary that scientists modify scientific theories when important new information is discovered? A. To confuse the scientists B. To keep the theory interesting and refresh C. To keep the theory as accurate and effective as possible D. To make sure the general public does not understand the theory 4. Which of the following best describes why scientists discuss and debate on Experiment al results and possible explanations in studying phenomena? A. Because debating helps scientists to analyzing both the strength and weakness of empirical evidence B. Because debating helps the scientists to present interesting and exciting science to the public General Science Grade 7 Student’s textbook 27  Unit 1 : Basic Concepts of Science C. Because debating gives the scientists the opportunity to express their feeling and opinion D. Because every scientist wants to find an accurate explanation and disproves other’s explanation 5. What is the difference between science ad technology? A. Science is the study of the natural world to gain knowledge, and technology is the use of that knowledge or practical purposes. B. Technology is the study of the natural world to gain knowledge, and science is the use of that knowledge for practical purposes. C. Science and technology are the same thing. D. Science has a direct effect on society than technology. 6. In the past people stored computer data on floppy disks. Eventually, people began to use compact discs with greater storage capacity. Which of the following best describes this situation? A. Technology leading to a less useful means of storage B. Technology being used to create a new need or want C. Technology being used to develop the designed world D. Technology leading to the development of new technology 7. Which of these is an example of technology helping a scientist? A. A scientist discusses a theory with different colleagues. B. A scientist determines whether to investigate a volcanic eruption. C. A scientist performs an Experiment in a laboratory setting. D. A scientist measures the mass of a chemical on a digital scale. 8. What would you use to measure length? A. Graduated cylinder B. Triple beam balance C. Meter stick D. Spring scale 28 General Science Grade 7 Student’s textbook  Unit 1 : Basic Concepts of Science 9. Which one best describes measurements that are accurate? A. They are very close to an accepted value. B. They are based on an estimate. C. They are very close to each other. D. They are not based on numbers. 10. Which one of the following is not a vector quantity? A. Displacement B. Force C. Density D. Velocity 11. Which one of the following is a derived SI unit? A. Newton B. Kelvin C. Kilogram D. Second 12. 2 hr. + 20 min + 60 sec are equal to ______ minutes. A. 120min B. 150 min C. 141min D. 161 min II. Answer the following questions briefly 13. Mention some examples of technologies in the field of communication, health, agriculture and education. Briefly explain the benefits you get from the technologies 14. Explain how human needs, science and technology are interrelated? 15. Does development in technology have risks? If so, mention some risks of advancement in technology? 16. What do you think are the importance of safety rules? 17. List laboratory apparatuses and write their uses. General Science Grade 7 Student’s textbook 29  Unit 2 : Matter in Our Surroundings Unit 2 Matter in Our Surroundings Learning outcomes: At the end of this unit, you will be able to:  Use particle theory‘s postulates to explain properties and behavior of materials.  Classify matter as an element, compound, homogeneous mixture, or heterogeneous mixture with regard to its physical properties.  Describe the structure of solids, liquids and gases in terms of particle separation, arrangement and types of motion.  Differentiate between physical and chemical properties and changes of matter.  Appreciate that matter can be classified based on physical or chemical properties.  Use properties of matter to identify substances and to separate them.  Demonstrate scientific inquiry skills along this unit: observing, classifying, comparing and contrasting, making models, inferring, communicating, asking questions, designing Experiment s, drawing conclusions, applying concepts. Activity 2.1 Take a spoon of sugar and grind it into a tiny pieces. Again continuously grind these pieces into a very fine powder. Next, dissolve the sugar in water Yet if you taste the solution, you know that the sugar is still there. 1. What do you think has happened to the sugar? 2. What do you think about the size and volume of sugar pieces? 3. Do you think the mass of sugar changed? 4. Write your conclusion about how matter is made of? 30 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings 2.1. Characteristics and nature of matter 2.1.1 Meaning and properties of matter Activity 2.2 In your home and class, you use many materials like tea cup, pen, textbook, shoes, and black board for different purposes. What do all these matters have in common? As you look at your surroundings, you see a large variety of things with different shapes, colors, sizes and textures. The air you breathe, the food you eat, stones, stars, plants, animals, a drop of water, a particle of sand, etc are forms of matter. Activity 2.3 In your surroundings you get or experience chairs, air, sound, light, banana, water, and smell of perfume. Which of them do you think have mass and occupies space and which do not? Anything that occupies space and has mass is called matter. Matter can exist in three physical states. These are solid, liquid, or gases. 2.1.2 Particulate nature of matter A. Particle model of matter Activity 2.4 Fill one graduated cylinder with 50 mL of sand and another graduated cylinder with 50 mL of water. Pour 50 mL of water into the graduated cylinder filled with 50 mL of sand. Observe carefully the air bubbles that rise to the surface. 1. What is the total volume of sand and water? 2. Why is the final volume less than 100 mL? 3. What do you conclude from this Experiment ? General Science Grade 7 Student’s textbook 31  Unit 2 : Matter in Our Surroundings The Particle Theory of Matter helps us to explain why different matters have different properties. The Particle Theory of Matter has the following key ideas: 1. All matter is made of tiny particles. 2. Particles of matter are attracted to each other. 3. Particles of matter have spaces between them. 4. Particles of matter are always in motion. 5. Temperature affects how fast particles move. 6. Particles of one substance differ from the particles of other substances. Experiment 2.1 Title: Demonstration of the particulate nature of matter. Objective: To demonstrate that matter is made up of smaller particles. Chemicals: Potassium permanganate crystal or ink and water. Apparatus: Beakers and spatula. Procedure: 1. Pour water into the beaker till it is half full. 2. Dissolve some potassium permanganate crystals or ink until the solution is purple. 3. Transfer half the solution into another beaker and fill it with water. 4. Continue the process with other beakers, comparing the color of the solution through each dilution. Observation analysis: 1. What happens to the color of the solution upon each dilution? 2. What does this signify? 3. What is your conclusion? 32 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings 2.1.3 Explaining observations using the particle theory of matter A. Diffusion and everyday effects of diffusion Activity 2.5 Spray a perfume from a corner of the classroom. (You can substitute perfume with burning incense (Etan) or sendel.) 1. Do you smell the perfume or incense? Why? 2. Why was it possible for you to smell from a distance? Diffusion is an evidence for the particulate nature of matter. It is the process by which particles of liquids or gases spread out randomly from a region of high concentration to lower concentration. Diffusion occurs because particles in a substance are always moving around. Particles of gases diffuse quickly. The particles of gases are moving fast as a result of very weak intermolecular forces between them. Liquids can also undergo diffusion. The rate of diffusion of liquids is slower than gases because liquids particles move more slowly due to strong intermolecular attraction force that held them. For example, if you drop a small amount of ink into a jar of water the color will spread slowly through the water by diffusion. Diffusion does not usually happen in solids because the particles in solids can only vibrate on fixed position due to very strong intermolecular attraction force that held particles of solids together. General Science Grade 7 Student’s textbook 33  Unit 2 : Matter in Our Surroundings B. Properties of solids, liquids and gases The differences in the properties of states of matter are given in the following Table. Table 2.1: Properties of solid, liquid and gaseous state Solid state Liquid state Gaseous state Have definite volume but no Gases have neither Have definite definite shape. Liquids attain definite shape nor definite shape and volume the shape of their container volume Are compressible to a small Are incompressible Are highly compressible extent The particles attract The force of attraction between The force of attraction is each other very liquid particles is weaker than much weaker than liquid strongly solid particles and solid particles Gaseous particles are Particles of solid These particles of liquids move in a continuous, freely cannot move freely freely random motion Particles are very Far apart particles compared to Very far apart particles much closer to each solids compared to liquids other C. Particles in solids, liquids and gases Activity 2.6 The following Figure s represent the three physical state of substances. Which of the following Figure s represent solid, liquid or gas? Explain. Figure 2.1: Physical states of matter 34 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings Observation and Analysis 1. In which state are the particles more closely packed? 2. In which state do you think the force of attraction is stronger? The particles in a solid are held together strongly. The spaces between solid particles are very small. A solid has a fixed shape and a fixed volume because the particles only vibrate at their fixed position. The particles vibrate back and forth but remain in their fixed positions. Gases always fill or occupy their entire container. Since the particles are moving constantly in all directions, they spread throughout their container, no matter what volume or shape their container is. D. Melting, solidification, condensation and evaporation Activity 2.7 1. If you hold a piece of ice on your hand for a few minutes what will happen to the ice? Why? 2. If a wet cloth is exposed outside to the sun, it will dry. Why? Where does the water go? 3. If you cool a bottle of water to a very low temperature in a fridge, what will happen to the water? 4. If you place a piece of butter on a hot pan, what will happen to the butter? Why? The change of a substance from a solid to a liquid state is called melting. The reverse of melting is called freezing or solidification. As a liquid cools, the particles in the liquid lose energy and move more and more slowly and then settle into fixed position. Thus the liquid has frozen or solidified. This process is called solidification or freezing. General Science Grade 7 Student’s textbook 35  Unit 2 : Matter in Our Surroundings Figure 2.2 Melting and Freezing When a liquid absorbs heat energy, the particles move more and more quickly. Some of the particles gain enough energy to break free of the other particles. When this happens, the liquid changes to a gas. The change of state of a substance from a liquid to a gas is called evaporation. Figure :2.3 Evaporation and Condensation The reverse of evaporation, i.e. the change of state from a gas to a liquid, is called condensation. As a gas cools, the particles in the gas lose energy and move more and more slowly until the gas condenses to a liquid. E. Compression Experiment 2.2 Title: Comparison of gases, liquid and solid. Objective: To compare compressibility of gas, liquid and solid. Materials: Three syringes of 100mL, 20 mL or 10 mL. Chemicals: Chalk powder or soil and water. Procedure: 1. Take three syringes with their pistons and close the nozzles of the syringes with rubber. 36 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings 2. Fill syringe I with chalk powder or soil, syringe II with water and syringe III already contains air. 3. Insert back the pistons of the syringes and push the pistons. Figure 2.4 Compression using syringes Observation and analysis: 1. What did you observe? 2. Why do you think you are able to push the piston of the syringe III containing air but it is difficult to push the piston of the syringes I and II? Compression is the process of close packing of particles by applying external force or increasing pressure. For example, when you inflate a ball it gets harder because of the air particles are collected and compressed into the ball and pushing on the inner walls of the ball. Activity 2.8 Take two balloons. Fill both the balloons with air. Place one of the balloons in a cold place. Place the second balloon in hot place (under direct sunshine). Which balloon explodes first? Why? General Science Grade 7 Student’s textbook 37  Unit 2 : Matter in Our Surroundings 2.2 Physical and chemical properties of matter 2.2.1 Physical properties of matter Activity 2.9 Consider materials in your surroundings such as water, common salt, sugar, wheat flour, copper wire, air, charcoal, oil, Observe the materials and answer the following questions. 1. Which of them are solids, liquids and which are gases? 2. Which of them do you think are soluble and which are insoluble in water? 3. Tell the colors of each substance to your friends? A physical property is a characteristic of a substance that can be observed without changing it into another substance. Physical properties include; Properties recognized by our sense organs such as; color, taste, texture, odor. State of substances as solid, liquid and gas. Properties like density, hardness, solubility, texture, conductivity of heat and electricity, melting point, boiling point, magnetic property, etc. 2.2.2 Identification of substances using physical properties Identification of substances can be done based on their physical properties such as color, solubility, taste, texture, odor, state of substances density, hardness, melting point, boiling point, etc. 38 General Science Grade 7 Student’s textbook Unit 2 : Matter in Our Surroundings Experiment 2.3 Title: Identification of substances based on their physical properties. Objective: To investigate the physical state and solubility of substances. Materials required: Four small beakers, a spatula and glass rod. Chemicals: Five different substances (common salt, oil, sand, sugar and water) Procedure: 1. Examine each of the substances and record your observation about their physical state. 2. Take four small beakers and add 50 mL water to each beaker. Then, add one spatula of each substance to each beaker. Stir the mixture in each of the four beakers with a glass rod and observe the solubility of each substance. Observation and analysis: Copy the following Table in your exercise book and record your observa- tions. Soluble or insoluble in wa- Substance State Color ter Common salt Oil Sand Sugar 1. Does each substance have the same state after added in water? 2. Can we consider solubility of substances in water, as a physical property? Why? General Science Grade 7 Student’s textbook 39  Unit 2 : Matter in Our Surroundings 2.2.3 Chemical properties of matter Activity 2.10 Bring a small amount of milk, a lemon, paper, match, nail, tea cup to the class. 1. Add small amount of milk into a cup. Add the lemon juice into milk and mix them together. 2. Tear pieces of paper and lit it with a burning candle for 30 seconds carefully. 3. Touch one end of the nail with a burning candle for 30 seconds carefully. Based on the above practical activities, answer the following questions. a. What did you see on the milk after a lemon juice is added on it? b. What did you see on paper and nail? Which one of them burns easily? c. What do you understand from the above activities? A chemical property is a characteristic of a substance that describes its ability to be changed into a new substance. To observe the chemical properties of a substance, you must try to change it to another substance. For example, Wood can catch fire and burns in air forming new substances water and carbon dioxide. Burning or flammability, reaction of a substance with acids, water, air etc. are some examples of chemical properties of substances. Chemical properties can be used to classify substances. 2.3. Classification of substances with composition and observable properties Activity 2.11 Group the following substances into pure substances or mixtures. Table salt, pure water, blood, copper, aluminium, soil, sulfur, air, oxygen , carbon, tea, oil, and milk. 2.3.1 Pure substance and mixture Substances around us can be classified as pure substances and mixtures. A pure substance is a material, in which all its samples have fixed composition and dis- 40 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings tinct properties. Elements and compounds are pure substances. All the samples of a given pure substance are chemically the same. Activity 2.12 Based on your lower grade knowledge, write the type of matter on the space provided in the chart. Matter Pure substance Mixture Element Homogeneous Metal A. Elements and compounds Elements Elements are made of tiny invisible particles called atoms. An atom is the smallest particle that has the properties of an element. 118 elements have been known until now. 92 of the elements are naturally occurring. The rest are man made. Each element is made of one kind of atom. Classification of Elements Activity 2.13 Like animals or plants living in your surroundings, elements are all different, but they have some properties in common. Collect the following materials from your surrounding: Aluminum sheet, copper wire, and charcoal (carbon), sulfur and compare the following properties. Which one of them do you think; a. is shinny or not? b. can easily bent or flattened into shapes? c. can be broken easily? d. is/are conductor(s) or not? e. have common properties with others? General Science Grade 7 Student’s textbook 41  Unit 2 : Matter in Our Surroundings The elements can be classified as metals, nonmetals, or metalloid. Metals A metal is a substance that conducts heat and electricity well. Metals are usually solid at room temperature except Mercury. They are shiny when polished. Metals can be bent or flattened into shapes without breaking. That is, they are malleable and ductile. Some metals are heavy having high density while and some them are light that have relatively low densities. Examples of metals: Aluminium, Iron, Copper, Gold, Silver, Calcium, Sodium, etc. Nonmetals A nonmetal is an element that is a poor conductor of heat and electricity except carbon in the form of graphite. Nonmetals that are solid at room temperature will break rather than bend. These elements do not usually shine when polished. Sulfur and carbon are examples of solid nonmetals. Most nonmetals are gases at room temperature. Some examples of gaseous nonmetals are helium, nitrogen, and oxygen. Bromine, is a liquid nonmetal at room temperature. Experiment 2.4 Title: Identification of physical properties of metals and nonmetals. Objective: To identify physical properties of metals and nonmetals. Materials required: Copper, iron, aluminium, lead, sodium metal, and a magnet. Properties of metals and nonmetals Procedure: 1. Take a magnet and check if the above metals are attracted by the magnet. Which metals are attached by the magnet and which are not? 2. Examine each metal carefully. Your record should include physical state, the color of the metal, and whether the element is magnetic or nonmagnetic. 42 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings 3. Repeat steps 1 and 2 for nonmetals. Elements Color State Magnetic or nonmagnetic Copper Iron Aluminium Lead Charcoal (Carbon) Sulfur Observation and analysis: 1. Which element can be identified by its reddish-brown color? 2. Which element is silvery-white in color? 3. Which element is black in color? 4. Which element is grayish in color? 5. Which of the elements can be attracted by a magnet and which of them are not? Metalloids Metalloids are a very small group of elements that have some properties of the metals and that of nonmetals. Metalloids are not as good conductors of heat and electricity as the metals, but they are better conductors than the nonmetals. Boron, Silicon, and Germanium are examples of metalloid. Compounds Compounds are pure substances composed of two or more elements that are chemically combined. A compound can be represented by a chemical formula, which shows the types of elements and the ratio of elements in the compound. General Science Grade 7 Student’s textbook 43  Unit 2 : Matter in Our Surroundings Activity 2.14 I. Which of the following are compounds and which are not? Why? 1. Mercury 2. Calcium chloride 3. Nitrogen gas 4. Copper oxide II. Write the elements form which the following compounds are formed. 1. Sulfur trioxide 2. Sodium chloride 3. Calcium oxide B. Mixture Activity 2.15 Bring some amount of water, sugar, salt, sand and five beakers or any container to your class. In separate beakers, mix water and sugar, water and salt, water and sand, sugar and salt, and salt and sand. 1. In which of the mixtures can you see the components after mixing? Why? 2. In which mixtures do the components cannot be seen after mixing? Why? Most of the substances you see every day in our surrounding are mixtures. A mixture is made of two or more pure substances such as elements, compounds, or both, that are mixed physically. Each substance in a mixture keeps its individual property. And also, the components of a mixture are not always composed or mixed in a fixed ratio. 44 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings Figure 2.5: Heterogeneous Mixture of fruits Homogeneous and heterogeneous mixture A mixture can be heterogeneous or homogeneous. A heterogeneous mixture is defined as a mixture in which the component parts can be seen with a naked eye or with a help of microscope. A soil is an example of a heterogeneous mixture consisting of particles of sand and clay, humus, microorganisms, water and air. Examples: a mixture of sodium chloride (Table salt) and sand, local bear, a mixture of sand and salt, blood, milk, etc. A homogeneous mixture is defined as a mixture in which the component particles cannot be seen with a naked eye or with a help of microscope. Suppose you stir a teaspoon of sugar into a glass of water. After stirring for a little while, the sugar dissolves, and you can no longer see crystals of sugar in the water. You know the sugar is there, because the sugar solution tastes sweet. Examples: a mixture of alcohol and water, clean air, salt solution, sugar solution, etc. General Science Grade 7 Student’s textbook 45  Unit 2 : Matter in Our Surroundings A. Salt solution B. A mixture of water and oil Figure 2.6: Illustration of: A- homogeneous and B-heterogeneous mixtures Table 2.2 Difference between homogeneous and heterogeneous Mixture Homogeneous mixture Heterogeneous mixture Has a uniform composition Has a nonuniform composition Has only one phase Has two or more phases Components cannot be seen with Components can be seen with necked eye necked eye or with a microscope or with a microscope 2.4 Changes around us: Physical and chemical change 2.4.1 Physical and chemical changes Activity 2.16 Obtain a small piece of chalk. 1. Observe it and record its properties. 2. On a piece of clean paper, crush the piece of chalk with the back of a metal spoon. Describe the changes that occur. 3. Place some of the crushed chalk into the bowl of the spoon. Add about 8 drops of vinegar. Describe what happens. a. Do you think a new substance was formed when the chalk was crushed? 46 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings b. Do you think a new substance was formed when vinegar was added? Provide evidence for your answers. Think It Over: Mostly chalk is a single substance, calcium carbonate. Physical Change In what ways can matter change? There are two types of changes in nature; physical and chemical changes. A physical change is any change that alters the form or appearance of matter but does not form a new substance. A substance that undergoes a physical change is still the same substance after the change. Examples: Powdering of chalk, dissolving of salt in water, melting of ice, evaporation of water, etc. Chemical Change A change in matter that produces one or more new substances with new properties is a chemical change, or a chemical reaction. Examples: Burning of charcoal, rusting of iron, fermentation, photosynthesis in plants, etc Table 2.3: Difference between physical and chemical changes Physical change Chemical Change Results in no change in chemical Results in a change in chemical identities of the substance identities of the substance New substances with new properties No new substance is formed are formed The change is easy to reverse It is difficult to reverse the change Result in no change in the composition Results in a change in the composition of the substance of the substance Energy changes is not necessarily Energy change ( mostly heat change) involved is involved. General Science Grade 7 Student’s textbook 47  Unit 2 : Matter in Our Surroundings 2.4.2 Importance of physical and chemical changes in our life Activity 2.17 Consider the changes like melting butter, cooking eggs, erosion of soil, burning wood to cook food, dissolving sugar in tea, making yogurt, and chopping wood, hammering metal to make knife, rusting of iron, spoiling of food. 1. Which ones do you think are physical changes? Why? 2. Which ones do you think are chemical changes? Why? 3. Which ones do you think are harmful and which are useful changes? Why? Write a group report. Mostly things we found in nature are not directly used as they are, but we have to modify them to fit our purpose. For example, to prepare bread or injera, the teff or the wheat must be grinded to get flour. This is a physical change. But the rising of the dough and the cooking process involves chemical change. We break wood into smaller pieces for burning while cooking food. The breaking of wood is a physical change but the burning of wood is a chemical change. Crushing of stone for construction, melting and molding of metals to make tools, evaporation of water to get salt from sea water, melting of butter or honey, milling of grains like wheat and corn are some examples of important physical changes in everyday life. Cooking food, burning wood or charcoal for cooking food, burning gasoline or kerosene in cars and machines, preparation of Tej or Tella by fermentation of starch in grains like corn or sorghum, baking injera or bread, souring of milk, respiration process, etc. are some examples of important chemical changes in everyday life. Activity 2.18 From your day to day activities observe and record four changes and identify whether they are physical or chemical changes. Give your reasons why the changes are physical or chemical changes? 48 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings Project work Activity 2.19 There are peoples preparing local beer (Tella) and Arakie in your Villages Write all the types of physical and chemical processes /changes /taking place during preparation of Tella and Arakie. 2.4.3 Useful and harmful changes Activity 2.20 List examples of harmful and useful changes (physical and chemical changes) in the following Table. Harmful Change Useful Change What should do we minimize the harmful changes? Some uses of physical changes 1. Freezing enables us to store and preserve meat and other food products for a long period of time. This is very useful because microorganisms such as bacteria and molds that cause the spoilage of foods die in cold places. 2. Cutting a piece of cloth to be made into shirts or any other material that can be useful is an important change. 3. Grinding of teff is useful for preparing injera. 4. Evaporation of sea water is used to get salt. General Science Grade 7 Student’s textbook 49  Unit 2 : Matter in Our Surroundings Uses of chemical change 1. Animals make use of chemical reactions to convert the food they eat to obtain energy. 2. Plants undergo photosynthesis to combine carbon dioxide and water to form glucose or sugar. 3. Changing wood into charcoal for cooking food is also another example. 4. Preparations of Tella, Tej, and bread. 5. Preparation of medicines, plastics, fertilizers and other important goods involves chemical changes. 6. Chemical industries produce their products through chemical changes. Useful materials like soap, ceramics, glass, plastics and paper are prepared by chemical changes. There are also chemical changes that are harmful such as the rusting of iron, decaying of food and explosion of bombs. 2.5 Separation of mixtures and its application Activity 2.21 Tea leaves are separated from the liquid with a filter. Milk is churned to separate the butter. We gin cotton to separate its seeds from the fiber. How do you separate sand mixed with salt in glass of water? Write your steps and present to your classmates. Separation methods are those methods that can be used to separate mixtures into their components. Separation is an important processes used to purify components from mixtures. 50 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings 2.5.1 Methods of separation of mixtures Activity 2.22 1. Bring some amount of grain purchased from a shop or from your home to the classroom. Now, spread the grain on a sheet of paper. Do you find only one kind of grain on the sheet of paper? Are there pieces of stone, husks, broken grain and particles of any other grain in it? 2. Before grinding teff, you need to remove impurities that may be present in it. How do you remove the impurities? Both homogeneous and heterogeneous mixtures can be separated by physical methods. The method to be used is chosen based on the differences in physical properties of the components such as magnetic property, solubility, density, melting point, boiling point, etc. Some of the separation methods are decantation, filtration, evaporation, magnetic separation, using separatory funnel, simple distillation and fractional distillation. 1. Magnetic method of separation This method involves the separation of magnetic substances from nonmagnetic substances by means of magnet. Magnetic separation takes advantage of magnetism, so it is useful only for certain substances that are strongly attracted by magnet. Experiment 2.5 Title: Separation of mixture using a magnet Objective: To separate a mixture of iron and Sulfur using a magnet. Materials required: Magnet, iron filings, powdered Sulfur, beaker, sheet of paper/ watch glass, and spatula Procedure: 1. Take two spatulas of iron filings and powdered sulfur into a beaker, and mix them thoroughly. 2. Place a portion of the mixture on a sheet of paper/ watch glass. General Science Grade 7 Student’s textbook 51  Unit 2 : Matter in Our Surroundings 3. Bring a magnet close to the surface of the mixture as shown in Figure 2.7 Figure 2.7: Magnetic separation Observation and analysis 1. What type of mixture is it? 2. Which component of the mixture is attracted to the magnet? 3. What can you conclude from the Experiment ? 2. Evaporation method Evaporation is a method used to separate out mixtures where there is/are one or more dissolved solids. In this method the liquid component drives off from the solid components by applying heat. This is because liquid components will evaporate over time through heating. Evaporation is suitable to separate a soluble solid from a liquid. In many parts of the world, Table salt is obtained from the evaporation of seawater using heat energy from the sun. Experiment 2.6 Title: Evaporation Objective: To separate salt from a salt solution. Materials required: Burner, evaporating dish, tripod, wire gauze, salt, beaker, watch glass, beam balance, measuring cylinder. 52 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings Procedure: 1. Dissolve about 10g of common salt (NaCl) in 30 mL of tap water in a beaker. 2. Pour the salt solution in to an evaporating dish as shown in Figure 2.8. 3. Boil the solution until all the liquid evaporates and observe the result. Figure 2.8: The separation of salt from a salt solution by evaporation. Observation and analysis 1. What did you observe in the evaporating dish? 2. What would happen to the level of the liquid if the evaporating dish is covered with a watch glass? Is evaporation possible? 3. Sedimentation, Decantation and Filtration Activity 2.23 Collect some muddy water from a pond or a river. If it is not available, mix some soil to water in a glass. Let it stand for half an hour. Observe the water carefully and note your observations. Does some soil settle at the bottom of water? Why? What do you call this process? Sometimes, it may not be possible to separate components of a mixture by winnowing and handpicking. For example, there may be lighter impurities like dust or soil particles in lentils (misir) or peas. How are such impurities separated from lentil or pea before cooking? General Science Grade 7 Student’s textbook 53  Unit 2 : Matter in Our Surroundings Lentil or grains are usually washed before cooking. When you add water to these, the impurities like dust and soil particles get separated. These impurities washed out into water, which becomes a little muddy. Now, which will deposit to the bottom of the container lentil or dust? Why? Have you seen that the container is tilted to pour out the dirty water? When the heavier component in a mixture settles after water is added to it, the process is called sedimentation. When the water (along with the dust) is removed, the process is called decantation. Experiment 2.7 Title: Decantation Objective: To separate a mixture of liquid and insoluble solid denser than the liquid component. Materials required: Two beakers, glass rod, sand, and water. Procedure: 1. Put water and sand into a beaker, and stir them thoroughly. 2. Allow the mixture in a beaker for one minute to settle down the insoluble solid. 3. Pour the liquid above solid into another beaker as shown in Figure 2.9. Figure 2.9: Decantation of muddy water Observation and analysis 1. Which component of the mixture was sedimented? 2. What can you conclude from the Experiment ? 54 General Science Grade 7 Student’s textbook  Unit 2 : Matter in Our Surroundings Filtration is a separation method used to separate out insoluble substances in a mixtures comprised of particles of which some are large enough in size to be captured with a filter paper. Particle size can vary considerably, in a given type of mixture. For instance, water filters can filter out bacteria (of length in order of 1 micron) and soil particles from stream water. Such process of separating insoluble particles that cannot pass through the pores of a filter paper is called filtration. Experiment 2.8 Title: Filtration Objective: To separate a mixture of chalk (insoluble) and water by filtration. Materials required: Beakers, filter paper, funnel, flask, powdered chalk and water. Procedure: 1. Put powdered chalk into a beaker containing water, and stir the mixture to mix them. 2. Pour the mixture into the funnel fitted with a filter paper and collect the filtrate in t