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SCIENCE REVIEWER General Science Definitions of Science An organized body of knowledge gathered over a long period of time to explain the world we live in. Knowledge or a system covering general truths or t...

SCIENCE REVIEWER General Science Definitions of Science An organized body of knowledge gathered over a long period of time to explain the world we live in. Knowledge or a system covering general truths or the operation of general laws especially as obtained and tested through scientific method. Scientific Method 1. Identifying the problem (Questioning) 2. Gathering Preliminary data 3. Formulating a hypothesis* 4. Testing of the hypothesis 5. Analysis and Interpretation of data 6. Drawing of Conclusion Independent Variable – variable changed by the experimenter Dependent Variable – variable that responds to the variable that is changed in the experiment. Experimental group – groups that receive treatment. Control group – opposite of Experimental. hypothesis – it is what we think the answer to the question is and it should stated in terms of the variables defined. Laws and Theories *Scientific law – a description of a natural occurrence that has been observed many times. *Scientific theory – a reasonable explanation of a scientific law. It is derived from a hypothesis that has been supported by repeated testing. *Model – helps visualize occurrences and objects that cannot be observed directly. Note: Scientific laws and theories cannot be proven absolutely. They are maintained as all observations support them. Measurements In science, the metric system is used in all measurements for its convenience and simplicity. The International System of Units (SI) uses the seven base quantities and units given below: Physical Quantity Unit Name (symbol) Mass Kilogram, kg Length Meter, m Time Second, s Amount of Substance Mole, mol Temperature Kelvin, K Electric current Ampere, A Luminous intensity Candela, cd 1  A. Reading Metric Measurements No. of significant digits = no. of certain digits + one certain digit (0 or 5) Example 1: The diagram below is a metric ruler used to measure the length of a pencil. How long is the pencil? 8 cm 9 10 The smallest fraction of a centimeter in the metric ruler is 0.1 cm. This corresponds to the last certain digit in any measurement. The pointer reads 9.0 cm. One uncertain digit should be added. In this case it is 0. Answer: Length of pencil = 9.00 cm B. Converting Metric Units Conversion of metric units is easily performed, Mega 106 Decimal point Kilo 103 moves to the left Deka 102 Hector 101 Base unit 100 Deci 10-1 Decimal point Centi 10-2 moves to the Milli 10-3 right Micro 10-6 Example 2: How many grams are there in 37.d centigrams? To convert 37.5 cg to grams, count the number of steps from centi to base unit. Since it moves upward, the movement of the decimal point is to the left. Answer: 0.375 g Major Regions of the Earth 1. Lithosphere – the solid part and the largest portion of the earth 2. Hydrosphere – the liquid part. It covers about 71% of the earth’s surface 3. Atmosphere – the gaseous portion that envelops the earth 4. Biosphere – the region where living things are found. Rocks and Minerals Everywhere you look, you find rocks of different shapes and sizes. What is important to remember about rocks is the way they were formed. The varying conditions for the rock formation influence the characteristics that each rock develops, Igneous rocks – formed from hardened magma and lava. e.g. Rhyolite, Granite, Basalt, etc. Sedimentary rocks – form from deposited fragments or particles of other rocks that have been weathered and eroded. e.g. limestone, conglomerate, dolomite, shale 2  Metamorphic rocks – rocks that have undergone changes due to heat and pressure e.g. marble (from limestone), slate(from shale) * Rocks are made up of minerals which are either elements or compounds. Weathering is a term for all processes which combine to cause the disintegration and chemical alteration of rocks at or near earth surface. Erosion includes all the process of loosening, removal, and transportation which tend to wear away the earth’s surface. Lithification is the conversion of unconsolidated sediment into solid rock. Weather and Climate Meteorology – the study of the earth’s atmosphere, weather and climate Weather – the daily condition of the earth’s atmosphere Climate – general conditions of temperature and precipitation in a large area over a long period of time. Gases found in the atmosphere: a. Nitrogen – about 78% - nitrogen in air reacts with chemicals to produce nitrates, which are used by living things for the manufacture of proteins - is returned to the atmosphere by the process of decay b. Oxygen – 21% -used for respiration -for combustion processes c. Other gases – (water vapor, CO2, O3) Layers in the atmosphere 1. Troposphere – layer where life exists - where different weather conditions prevail - has lowest temperature 2. Stratosphere – contains ozone that serves as a protective shield against UV rays. - where jetstream is found 3. Mesosphere – layer where meteoroids that enter the earth’s atmosphere are burned. 4. Ionosphere – contains ions that are used for radio communications 5. Exosphere – orbit space for artificial satellites. The uneven temperature and pressure in the atmosphere result in the movement of air called winds. Monsoons are examples of winds that result from the differences in the absorption and reflection of thermal energy by different materials of Earth. Ecology 1. Ecology – the study of how living things interact with their environment. 2. Ecological Factors a. biotic – all living factors in the environment b. abiotic – nonliving factors that are essential to living organisms 3. Population – a group of the same species living together 4. Community – all the different populations living together 5. Ecosystem – community of different living things interacting with one another and with their nonliving environment 3  6. Biomes – a large area whose ecological communities are determined by its climate. Solar System The probable origin of our solar system, specifically the sun, is similar to that of other stars. The age of a star is related to its temperature and its color. Bluish and white stars are the hottest and youngest stars. The least hot and the oldest star are the reddish stars. Nebular theory – states that the solar system originated from a rotating gas and dust cloud composed of hydrogen, helium and some heavier elements. Ptolemaic Theory – The earth is stationary; each planet and the sun revolved around the earth. Copernican Theory – This theory considers the sun as the center of the solar system. The earth and other planets revolve around the sun in a circular orbit. Planets - Mercury- Rocky, cratered surface; extremely thin atmosphere - Venus-Thick cloud cover; green house effect - Earth-liquid water, life - Mars-polar ice caps, pink sky, dominant volcanoes - Jupiter-Great red spots, thin ring; huge magnetosphere - Saturn-many rings and ringlets, Titan only moon with substantial atmosphere - Uranus-Rotates on side; worldwide ocean of superheated water - Neptune- Unusual satellite rotation, 4 rings, great dark spot. Asteroids - are objects that orbit the sun like planets. However they are smaller than the planets and so they are sometimes called minor planet. Meteoroids – are objects smaller than the asteroids that revolve around the sun. Comet - is a mass of frozen materials such as water, methane and ammonia along with the bits of rock and dust. Solar eclipse – when the sun, the moon and the earth are in straight line. During solar eclipse, the sun can’t be seen from earth because the moon covers it. Lunar eclipse – same as solar but in this case the sun covers the moon. 4  EXCERCISES FOR GENERAL SCIENCE II. Match each definition in column B with the correct word in column C. Write the letter of the correct word and the first letter of the correct word in the space provided in column A. A B C 1. A systematic process of gaining information a. Law 2. A variable that is changed by the experimenter b. Theory 3. It responds to the variable that is changed in the c. Scientific experiment method 4. A process that results to the breaking of rocks into smaller d. Independent pieces variable 5. Process by which infrared radiation from the earth’s surface e. Dependent is absorbed by water vapor and carbon dioxide in the variable atmosphere f. Weathering 6. It is a description of a repeatable natural occurrence g. Igneous rock 7. A reasonable explanation of natural occurrences h. Research 8. A sample group that receives a treatment i. Troposphere 9. Helps visualize occurrences and objects that cannot be j. Minerals observed directly k. monsoon 10. An educated guess. l. Model 11. A change in constitution of a rock brought about by m. M pressure and heat within the earth’s crust etamorphism 12. Solid earth materials that have a definite chemical n. Tide composition and molecular structure o. Greenhouse 13. A logical conclusion that can be drawn from an observation effect 14. This is done to gather important information before p. Hypothesis designing an experiment. q. Experimental 15. A periodic rise and fall of ocean water caused by the moon group and the sun. r. Inference 16. The layer of the atmosphere where we live s. Control group 17. Seasonal wind that blows between continent and an ocean t. Conclusion 18. Produced by the cooling and crystallization of molten lava u. Erosion or magma v. Sedimentation 19. Process of transporting rock particles w. M etamorphic rocks x. rocks II.Computation 1. An adult inhales 10 000 L of air a day. What is the equivalent volume in cubic millimeters? 2. One stick of cigarette of a particular brand contains 40 mg tar. If a person smokes 20 cigarette sticks in a day, how many grams of tar does he consume in a week? 3. The nearest star to the sun is 2.52 x 1013 miles away. How far is this in kilometer? III.Essay 1. What is the difference between revolution and rotation? 2. Unlike earth, which is surrounded by sea of gas, Mercury has no atmosphere. State a possible explanation for the lack of atmosphere in this planet. 5  Biology Biology – the branch of science that deals with the study of living systems and life processes. A. Cells This is probably the most basic term that you would need to know. All living systems are composed of cells. They are the basic unit of structure and fuction in living things. Following is an illustration and concept map of a cell and the different structures contained in it. Cell wall/cell membrane Except for the mitochondrion chloroplast Cell nucleus ribosome Except for the Endoplasmic reticulum Golgi apparatus cytoplasm lysosome protoplasm centriole Microtubules and microfilaments Organelles are structures with specific functions found within living cells.  Nucleus – This organelle is arguably the most important structure in the cell because it serves as the control center in which individual functions of the other organelles are coordinated.  Cell wall/cell membrane – the cell wall in plant cells and in some monerans and protests provides rigidity for support to the cells and a characteristic shape for functionality and structure. The cell membrane on the other hand is selectively permeable.  Mitochondrion – this organelle is also called as “powerhouse of the cell”. It serves as the site where ATPs are abundantly synthesized.  Chloroplast – this serves as the site of photosynthesis among plants and photosynthetic algae.  Ribosome – this serves as the site of protein synthesis.  Endoplasmic Reticulum – These organelles serve as channels or passageways through which materials are transported to the different parts of the cell.  Centriole – this serves for cytokinetic purposes and is very common among dividing cells  Lysosome – the structure is also called “suicidal bag” as it releases digestive juices  Golgi apparatus – this serves for selection and packaging of cellular materials. Differences between plant and animal cells Structure Plants Animals 1. cell wall Present Absent 2. chloroplast Present Absent 3. centriole Absent Present 4. lysosome Absent Present 5. vacuole One/large Many/small 6 How did the concept of the cell come about? The Cell Theory serves as the basis on which everything that we know about the cell is anchored. There are three elements to this theory; 1. All living things are made up of cells. 2. Cells are the basic unit of structure and function in living systems. 3. All cells come from preexisting cells. Like any biological structure, the cell is composed of biomolecules that are intricately combined to enable the cell to perform its metabolic functions. a. Carbohydrates – immediate source of energy - elemental composition: C, H, O - building blocks: monosaccahrides - e.g. sucrose (table sugar), maltose, amylase b. Fats/Lipids – these molecules serve as another source of energy after carbohydrates - elemental composition: C, H, O - building blocks: fatty acids and a glycerol backbone - e.g. waxes, oils, and cholesterol c. Proteins – these molecules serve as sources of building materials. - elemental composition: C, H, O, N, S - building blocks: amino acids - e.g. amylase, actin and myosin d. Nucleic Acids – these molecules include the RNA’s and the DNA’s - elemental composition: C, H, O, N, P - building blocks: nucleotides Cells according to complexity Prokaryotic cells – have no membrane-bound nucleus and organelles; typical of bacteria and blue-green algae Eukaryotic cells – have membrane-bound nucleus and organelles; typical of protests, fungi, plants, and animals. Cell Transport Passive Transport – does not require the expenditure of energy; moves particles through the concentration gradient. Active transport – requires the expenditure of energy; moves particles against the concentration gradient. Diffusion - this refers to the process in which molecules of solvent move from an area of high concentration to an area of low concentration. Osmosis – this refers to the diffusion of particles or molecules across selectively permeable membrane. Cell Reproduction This refers to the process by which cells divide to produce daughter cells. It involves either mitosis if somatic or body cells are involves or meiosis if germ or sex cells are involved. Mitosis - refers to the division of the somatic cells - also referred to as equational dvision because the ploidy number of the daughter cells is equal to the ploidy number of the dividing cell. 7 Meiosis - refers to the division of germ cells - also referred to as reductional division because the ploidy number of the daughter cells is only half that of the parent cell. B. Botany Plants are autotrophic organisms capable of synthesizing their own food for growth and maintenance through the process of photosynthesis. Their cells are eukaryotic (i.e. with a distinct nucleus and other membrane-bound organelles) like fungal and animal cells, but are distinguished by the presence of cellulosic cell walls, plastids and large vacuoles. Plant cells may also contain non-living inclusions called ergastic substances that are products of the cell’s metabolism, like crystals and starch. Major plant cell types: Three major plant cell types, parenchyma, collenchyma and sclerenchyma, make up the different tissues of the plant. Although they assume various shapes, they are most easily distinguished by general features and location in plant body. o Parenchyma cells are usually large, thin-walled and are extremely variable in shape. o Collenchyma cells have primary cell walls that are thickened irregularly by cellulose and pectin materials. o Sclerenchyma cells have a comparatively thick primary cell wall bearing heavy depositions of lignified secondary substance laid down in a laminated pattern. Tissues are aggregate of cells with similar structure and function. Some of the cells in the tissue may even undergo further cell modification and change in function. Thus it is difficult to classify plant tissues on the basis of a single criterion like function, origin or structure. o Meristematic tissues are composed of immature cells and regions of active cell division. They provide for growth and are found in the root tip. o Permanent tissues a. Epidermis –composed of tiny openings principally on the underside of the leaves that regulate the exchange of water and gases called stomates. b. Periderm – constitute the corky outer bark of trees. c. Vascular tissues – composed of xylem and phloem; xylem functions for the transport of water and minerals upward from the roots while phloem functions for the transport of food materials. Different Plant Parts Root It is typically underground organ of the plant axis that functions principally for anchorage and absorption of water and minerals from the soil. The first formed root is the primary root. It develops from the radicle of the seed embryo. Some root arises from other plant organs like stems and leaves hence are described as adventitious. There are two general types of root system, the fibrous which is found in monocotyledons, and the taproot, characteristic of dicotyledons. Stem The stem is readily recognized by the presence of nodes. Leaves are born on these nodes. The intervening area between the two nodes is an internode. Leaf It is a flattened, green, lateral appendage that carries out the functions of photosynthesis and transpiration. Chlorophyll gives the leaf its green color. 8 Flower It is a modified branch representing the reproductive structure of an angiosperm. It is generally divided into four parts: the green sepals, brightly colored petals, the male structure stamen, and the female structure known as pistil (carpel). Each of these has a collective term, respectively, the calyx, corolla, andorecium and gymnoecium. Fruit The fruit is the ripened ovary with functions to protect and disperse the seeds. It is the product of the entire pistil and other floral parts that may be associated with it. Two processes precede fruit development; pollination or the transfer of pollen from the anther to the stigma and fertilization or the fusion of a sperm nucleus and an egg cell. Photosynthesis and Transpiration Photosynthesis and transpiration are physiological processes occurring in leaves. Photosynthesis involves the trapping of the radiant energy and its conversion into chemical energy. It takes place in the chloroplast of the leaves. Transpiration is the loss of water in vapor form through the stomates, minute openings distributed on the surface of leaves. A stoma has a pair of epidermal cells called guard cells. Water moving into the guard cells cause latter to be turgid thereby opening the stomal pore. When the water moves out of the guard cells, these become flaccid and the stomal pore closes. The numerous stomates of a leaf serve as entry point for a carbon dioxide (photosynthesis) and the exit for water vapor (transpiration). If transpiration proceeds at a rate much faster that that of the roots could absorb water from the soil, the plant tissues suffer from water deficit, causes plant to wilt. General Equation: Photosynthesis: 6 CO2 + 6 H2O C6H12O12 + 6 O2 Respiration C6H12O12 + 6 O2 6 CO2 + 6 H2O - it is a complex process by which energy in the form of ATP is released from food molecules ingested by organisms. Plant Taxonomy It is the science of classification, nomenclature and identification of plats. It is the most basic and a unifying field of botany. Classification is the arrangement of plants into categories that have similar characteristics. These categories called taxa are arranged into hierarchy to form a classification system. The smallest taxonomic unit is the species. Similar species form a genus and elated genera, a family. The most inclusive category, the kingdom comprises all plants. Nomenclature is the orderly assignment of names to taxa or categories in accordance with the rules of International code of botanical nomenclature. A plant’s scientific name is a binomial, that is, it is composed of a generic name (genus) and a specific epithet. The name of the person who proposed the binomial completes the scientific name (Oryza sativa L.) C. Genetics Genetics is the study of heredity and variation. Heredity is the transmission of traits from generation to generation while variation deals with genetic differences between organisms. The process mainly involved in heredity and variation is cell division. 9  The cells in all organisms grow and reproduce by cell division. A unicellular bacterium, after doubling in size, can reproduce by dividing into two cells. In multicellular organisms like man, increase in size is attained by dividing its constituent cells. Gene Segregation and Interaction Dominant Allele - alternative trait that is expressed in the phenotype. Recessive Allele – alternative trait whose expression is marked in the phenotype. Law of Dominance – state that only dominant alleles are expressed in the phenotype and that recessive alleles are masked among hybrids but are manifested among pure breeds. Law of Co-dominance – states that two equally dominant alleles are equally expressed in the phenotype and that no blending is achieved. Law of Incomplete Dominance – states that among multi-allelic traits, two dominant alleles that are not dominant enough to mask the expression of one another, are incompletely expressed in the phenotype, hence a blended trait is achieved. Mendel’s law may be separated into two rules: first, the law of Independent Segregation of Alleles and second, the Law of Independent Assortment. *Law of Independent Segregation states that the alleles in a gene pair separate cleanly from each other during meiosis. *Law of Independent Assortment states that the alleles of the different genes separate cleanly from each other and randomly combining during meiosis. These laws can be illustrated using monohybrid and dihybrid cross: a. Monohybrid Cross One of the pairs of alternative characters in sweet peas studied by Mendel waqs round vs wrinkled seed. These distinctive characters or traits are called phenotype while the gene or genetic content coding for these traits is the genotype. In example below, both parents are homozygous so that the round (P1) and wrinkled (P2) parents have the RR and rr genotypes, respectively. The gametes produced after meiosis by P1 is R and by P2 is r so the progeny of the first filial generation (F1) have heterozygous (Rr) genotypes. Since R is dominant over r, then the F1’s have round phenotype. This is an example of complete dominance. R masks the expression of r. This is the dominant allele. The allele that is masked ( r ) is the recessive. Female Parent (P1) Male Parent (P2) Phenotype: Round Wrinkled Genotype RR rr Gametes R r Fertilization F1 genotype: Rr Phenotype; Round To demonstrate that the F1’s are heterozygous, a testcross can be conducted wherein the F1 plants are crossed to the homozygous recessive parents (rr). The recessive parent contributes 10 the gametes ( r ) while the other parent contributes R and r. Testcross results in 1 Rr (round): 1 rr (wrinkled) or 1:1 segregation ratio. Rr x rr Gametes r R Rr (round) r rr (wrinkled) Genotypic Ratio: 1Rr : 1rr Phenotypic Ratio: 1round : 1 wrinkled b. Dihybrid Cross The members of gene pairs located on different homologous chromosome segregate independently of each other during meiosis. Mendel studied two phenotypes, texture and color of seeds with two alternative traits; round and yellow seeds vs. wrinkled and green seeds. He crossed pure breeding round, yellow seeded plants with pure breeding wrinkled, green seeded plants. The F1 progenies were all yellow round seeded plants. The F2’s gave 315 round, yellow: 101 wrinkled yellow; 108 round, green and 32 wrinkled, green plants. Approximately 9:3:3:1. The method used in getting the genotypic ratio among F2 progeny is called Punnett Square or Checkerboard method. Molecular Basis of Heredity The first part dealt with the physical basis of heredity – the chromosomes. Chromosomes are the carriers of the multitude of genes. Genes or hereditary units, on the other hand, are actually fragments or portions of the deoxyribonucleic acid or DNA. A chromosome is made up of one very long DNA packaged with histones to fit inside a minute nucleus of the cell. Eukaryotic cells with several chromosomes would, therefore, contain more than one molecule of DNA. Prokaryotic cells and viruses generally possess one long molecule of DNA either naked or associated with proteins but not as organized as compared to eukaryotic chromosomes. The DNA has been tagged as the genetic material of all organisms with the exception of some viruses with ribonucleic acid or RNA as their genetic material. Central Dogma of Molecular Biology DNA as the genetic material is capable of transmitting biological information from a parent cell to its daughter cells and, in a broader perspective, from one generation to another. The information stored in its base sequence is copied accurately by replication. Replication is a process of faithfully copying a DNA to produce two DNA molecules identical to the parent DNA. These DNA molecules are then passed on to the daughter cells via the chromosomes during cell division. The information stored in the DNA when expressed will result to a particular trait of an individual. The trait is expressed through the action of proteins either directly or indirectly. The central dogma of molecular biology consists of three general processes namely: replication (DNA synthesis), transcription (RNA synthesis) and translation (protein synthesis). The transfer of information from cell to cell or from generation to generation is achieved by replication. On the other hand, the transfers of information from the DNA to the proteins involve two processes: transcription and translation. Generally, all organisms follow this mode of transfer except for some viruses that undergo reverse transcription. 11  Transcription Translation DNA RNA PROTEIN Reverse Transcription Mutation – changes in the genetic materials that are essentially heritable. a. Deletion – refers to a segment of base pairs in the DNA that is spliced off. b. Substitution – refers to a segment of the base pairs in the DNA that is replaced by a different series of base pairs. C. Translocation – refers to segments of base pairs that are differently positioned. d. insertion – refers to base pairs that are added to segment of DNA. Evolution – this process refers to the gradual change in populations through time. D. Animal Development (30 minutes) Animal Cells, Tissues and Tissue Organization Animal tissues are generally classified into four categories: Epithelium, Connective Tissue, Muscle and Nerve. These animal tissues make up all the organ systems of the body. o Epithelium, in its simplest form, is composed of a single continuous layer of cells of the same type covering an external or internal surface. o Connective Tissue, has the widest range encompassing the vascular tissue(blood and lymph), CT proper, cartilage and bone. o Muscular tissue consists of elongated cells organized in long units of structures called muscle fibers or muscle cells. The two general categories of muscle, smooth and striated. Striated or skeletal muscle functions for voluntary control while smooth muscle functions for involuntary contractions. o The nerve cells or neurons comprising the nervous tissue each possess a cell body which contains the nucleus and the surrounding cytoplasm. The process come in contact with other nerve cells, or with other effector cells through a point of contact called synapse. Animal Development Animal development is a series of events that is controlled by the genetic information in the nucleus and factors in the cytoplasm. It starts with fertilization and ends into the arrangement of cells which gives the embryo its distinct form. Features which are unique to organism such as the shape of the face, location and number of limbs and arrangement of brain parts are molded by cell movements in response to the action of genes in the nucleus and molecules in the cytoplasm. Stages of Development a. Gametogenesis 12  Each species has its own chromosome number. Somatic cells of humans have 23 pars of chromosomes (22 pair somatic and one pair sex; one chromosome of each pair is originally derived from the father and the other from the mother. The chromosomal pair comes in contact with each other and exchange segments during meiosis. This phenomenon provides combinations of parental traits hence there is more viability in the characters of the offspring. Gametogenesis changes the diploid cells into haploid sperms and ova. Cells undergo meiosis, a sequence of two divisions during which the chromosomes divide only once. The resulting cells have only half the number of the chromosomes of the parent cells. This process prevents doubling of the chromosomes during fertilization. The male germ cells, initially round and large, are changed into slender and flagellated cells. The cytoplasm is practically lost and mature cells develop a head, neck and tail. The female germ cells gradually increase in size as a result of growth. b. Fertilization The ovum and the sperm unite thus restoring the diploid chromosome number of the species. In humans, each gamete has 23 chromosomes (haploid). Upon fertilization the zygote acquires 46 chromosomes. At this stage of development, the genetic sex of the individual is established. c. Cleavage The unicellular zygote undergoes cleavage characterized by active mitoses. It is not a period of growth but a time in which the zygote is divided into a large number of small cells, the blastomeres. Each blastomere nucleus has the same DNA since these are derived from the same cell, the zygote. Cleavage ends with the formation of the multicellular organism. d. Blastula The mass of blastomeres forms a hollow fluid-filled cavity, the blastocoel. In frogs, cells below the blastocoel are large; these are the macromeres. In humans, at this embryonic stage, the 32-cell cell blastocyst burrows into the uterus. The blastocyst has two distinct cell types; an inner cell mass and an outer shell, the trophoblast. The former will become the embryo, the latter will give rise to the extra-embryonic membranes termed amnion and chorion. e. Gastrula Gastrulation, a stage of extensive cell movements, rearranges the embryonic cells. Cells are translocated to the different areas thus acquiring new neighbors and new positions. The neighbor cells may act as inducers in the formation of structures. The different cell movements establish the third germ layer, the mesoderm. At the end of gastrulation, the embryo has three primary germ layers: an outer ectoderm, an inner endoderm and middle mesoderm. At this stage tissues have become committed to form one type of organ- a brain or stomach. The ectoderm gives rise to the epidermis of the skin, sense organs and the nervous system. The endoderm gives rise to the organs of the respiratory and digestive systems. The mesoderm gives rise to the organs of the circulatory, skeletal, muscular, excretory and reproductive systems, connective tissues and linings of body cavities. f. Neurula Toward the end of gastrulation, the ectoderm along the dorsal surface elongates to form a layer of columnar cells, the neural plate. This region thickens and moves upwards forming the neural fold which then fuse to form a hollow tube, the neural tube. Closing of the neural tube starts 13 at the head region and continues posteriorly. This piece of tissue gives rise to skin pigments, nerves and the adrenal medulla. g. Organ formation The ectoderm, mesoderm and endoderm formed in the gastrulation are the source materials for the development of organs. At this stage the component cells are still undifferentiated and do not show any adult feature. These masses are further subdivided into groups of cells until the organ acquires its unique characteristics and specific location. h. Brain Formation The earliest form of the brain is the nueral tube. At this stage, the brain shows three regions- prosencephalon (forebrain), mesencephalon (midbrain) and the rhombencephalon (hind brain). Later, the prosencephalon divides into telencephalon and diencephalons. The mesencephalon remains undivided. In frogs, the brain is a straight tube and remains in that condition in adult. In humans, the embryonic brain undergoes bending and twisting. Hence in adult, the hindbrain is adjacent to the forebrain and the eyes become anterior to the nose. i. Limb Formation Limbs start as buds at the embryonic sides, which later develop as paddle-like extremities. Later, circular constrictions appear dividing the limb into three main segments. Fingers and toes develop when cells at the most distal end die. The upper limb rotates 90º sideward so that the thumbs move sideward. The lower limb rotates 90º towards the center, placing the big toe at the center. E. Ecosystem and Ecology The branch of biology that pertains specifically to the relationship of an organism with that of its environment is known as ecology. Ecology is a body of knowledge that covers the economy of nature. It involves the study of overall relationship of an organism to its inorganic/organic environment, that is, the physical world; and its relation and interaction with other organisms, both plants and animals alike. The basic functional unit and the most important concept in ecology is the ecosystem, as it includes both plants and animals and the physical environment, each of which influencing the other. Ecosystem or ecological system may refer to biotic assemblage of plants, animals, microbes interacting among them and with that of the physico-chemical environment. Components of the Ecosystem and Trophic Levels The ecosystem has two basic components – the biotic (living) and abiotic (non-living) components. The biotic component is further subdivided into two units, namely, the autotrophs (self nourishing/self feeding) and the heterotrophs (other feeding). The autotrophs are usually chlorophyll-bearing organisms, that are able to harness solar energy. In the presence of water and carbon dioxide, they convert this energy into (chemically- stored energy) known as adenosine triphosphate or ATP. They assume the role as producers in an ecosystem. Plants are the typical producers. However, in aquatic systems, algal communities or phytoplanktons may be the producers. Heterotrophs, on the other hand, are those that depend on the producers as food. They are generally classified as consumers, although those that secure food directly from the producers are better known as herbivores or primary consumers. A secondary consumer or carnivore, on the other hand, derives its nourishment indirectly from the producers by devouring the herbivore. In some ecosystems, tertiary consumers exist. Other heterotrophs include also the decomposers 14 where organic matter is reduced to simpler substances. Structurally therefore, the ecosystem can composite the following, that is, the abiotic factors; the producers; the macroconsumer; and the decomposers. The abiotic component, on the other hand covers climatic, edaphic (soil) and topographic factors. Climate includes light, temperature, precipitation and wind. Light influences the biotic components in many ways, as in photosynthesis, flowering seed dormancy, leaf senescence, nesting, migration and hibernation. Light quality penetrating with increasing water depths also determines the type of producers (i.e. green algae in shallow water and red algae at greater depths). Temperature affects living organisms by influencing their metabolic processes. It can determine the type of vegetation in different ecosystems depending on its availability. Water as the universal solvent plays an important role in the ecosystem as it serves as a medium for biochemical processes. It can determine the type of vegetation in terrestrial ecosystems depending on its availability. In aquatic ecosystems, however, what plays important roles are salinity, ph, temperature and dissolved oxygen. The atmosphere is a major reservoir of nutrients important to life. Nutrient cycling in the atmosphere is further facilitated by wind. The latter also accelerates evapo-transcription rate causing damage to plant structures. However, it plays an important role in facilitating seed dispersal and in the distribution of plants and animals. Biome - is a geographical unit uniformly affected by a common prevailing climate havin a similar flora and fauna. Terrestrial biomes the world over include:  Tropical rainforests – which have the highest species diversity  Coniferous forests – which harbors the pine-trees  Deserts – characterized by very low species diversity  Grasslands – also variously called savannahs, steppes and scrubs  Taigas and  Tundras-characterized by permafrosts Aquatic biomes on the other hand include:  Marshlands  Lakes  Seas and oceans and  Estuaries Five Kingdoms  Monera – prokaryotic; unicellular; includes the bacteria and the cyanobacteria.  Protista – eukaryotic; unicellular/colonial; includes the flagellates, the ciliates, the sarcodines and the algal systems.  Fungi – eukaryotic; unicellular (yeasts) and multicellular (molds and mushrooms).  Plantae – eukaryotic; multicellular;  Animalia – eukaryotic; multicellular; includes the invertebrates and vertebrates. Ecological Relationships a. Mutualism – “give and take” relationship b. Commensalisms- a relationship where the commensal is benefited and the host is neither benefited nor harmed c. Parasitism – a relationship where the parasite is benefited and the host is harmed d. Competition – neither organism in this relationship is benefited e. Predation – a relation where the predator is benefited and the prey is harmed 15 Food Chain Three components of a Food Chains a. Producers – occupies the 1st trophic level; composed of plants and photosynthetic algae b. Consumer - herbivore – occupies the 2nd trophic level; 1º consumer - carnivore – occupies the 3rd trophic level; 2º consumer - omnivore – occupies either the 2nd or 3rd trophic levels. c. Decomposer – the last component of a food chain Energy Transfer - energy is transferred from one trophic level to another following the 10 % rule. Food Web - it is a feeding relationship that is illustrative of a series of interlinking food chains. Ecological Laws Two ecological laws can demonstrate this relationship between organisms and their environment. These include Liebig’s Law of Minimum and Shellford’s Law of Tolerance.  Liebig’s Law of Minimum states that “growth and survival of an organism is dependent primarily on the nutrients that are least available. “A plant will grow and develop well where a particular nutrient critical for growth and survival is found to be inadequate or not available at all in that particular area. Take note that magnesium is an important component for the production of chlorophyll, being the central atom of pigment.  Shellford’s Law of Tolerance states that “the existence of the organism is within the definable range of conditions.” This means that “ organisms then can live within a range between too much and too little”. Thus an organism han an optimum range of conditions (peak) curve and an intolerance zone, where number of organisms is at its lowest or zero. Chemistry Chemistry- is a science that studies matter, its properties, structure and the changes it undergoes together with the energy involved. Branches of Chemistry  Analytical Chemistry  Physical Chemistry  Inorganic Chemistry  Organic Chemistry  Biochemistry Scientific method- a systematic approach/procedure in investigating nature; a combination of observations, experimentation and formulation of laws, hypotheses and theories; an organized approach to research 16 STEPS IN A SCIENTIFIC METHOD 1. Observation or Data Gathering Observations-things perceived by the senses; can be quantitative or qualitative Qualitative – consist of general observations about the system Quantitative – consist of numbers obtained by various measurements of the system Examples:  Ice floats in water  Vinegar is sour  Body temperature is 39.0oC  An object weighs 1.5 kg Observation vs. Inference Inference – interpretation of the observation e.g. The clouds are dark. (observation) It might rain. (inference) 2. Are the observations answerable by any natural law? Law (natural law) - a pattern or consistency in observation of natural phenomena; a verbal or mathematical statement which relates a series of observation e.g. Law of Conservation of Mass Law of Thermodynamics 3. Defining a problem 4. Formulate a possible solution (Hypothesis Making) Hypothesis- an educated guess to explain an observation; a tentative explanation of a natural law based on observation 5. Experimentation - Is the hypothesis really the answer to the problem? 17 6. Interpret results. 7. Generate a generalization. Theory- a hypothesis that survived testing through experimentation; a model or a way of looking at nature that can be used to explain and make further predictions about natural phenomena Laboratory Rules and Techniques  Do not return extra chemicals to the main supply unless so directed. To avoid waste, take from the supply only the amount of material needed.  Perform experiments with the apparatus at arm’s length from the body never directly under the face.  If you must smell a substance, hold the container at a distance and, with a cupped hand, waft the fumes toward your nose.  Never use cracked or broken equipment. It can complete its breaking.  Never pour water into concentrated acid. Always add the acid to the water with stirring.  Read the lower meniscus of a colorless liquid at eye level. Use the upper meniscus when the liquid is colored.  Never weigh hot substances. Measurements in Chemistry Rules on the Use of Significant Figures NON- ZERO DIGITS All non-zero digits are significant ZEROS IN MEASUREMENTS There may be some confusion about the zero in a measurement. Rules will be used to determine whether zeros are significant or not. 1. Trailing Zeros Final zeros after a decimal point are always significant. e.g. 25.330 g has 5 significant figures 2. Captive Zeros Zeros that are found between any two non-zero digits are significant. e.g 706.3 mm has 4 significant figures 3. Leading Zeros a. Zeros before a decimal point are not significant. e.g 0.786 g has 3 significant figures. b. When there are no digits before a decimal point or when the digit before a decimal point is zero, the zeros after the decimal point preceding other digits are not significant. e.g. 0.000543 cm3 has 3 significant figures 4. Final Zeros in a whole number may or may not be significant. To resolve this, use of exponential is recommended. EXACT NUMBERS Any number that is exact such as the number 3 in the statement “there are three feet in one yard” is said to have unlimited number of significant figures. ADDITION AND SUBTRACTION The sum or difference should have the same number of digits to the right of the decimal point as the factor with the least number of digits to the right of the decimal point. e.g. 35.986 18  + 675.8 567.3839 1279.1699  1279.2 (five significant figures) MULTIPLICATION AND DIVISION The result obtained by multiplication and/or division must have the same number of significant figures as the factor with the least number of significant figures. e.g (34.6)(3450.0)/345 =346.00  346 (three significant figures) RULES FOR ROUNDING OFF NUMBERS When the answer to a calculation contains too many significant figures, it must be rounded off to the proper number of significant figures. The rules for rounding off is summarized as follows: 1. If the digit to be removed is less than 5, drop this digit and leave the remaining numbers unchanged. Thus, 1.23 becomes 1.2 when rounded off to two significant figures. 2. If the digit to be removed is equal to or greater than 5, drop this digit and increase the preceding digit by one. Thus, 3.46 becomes 3.5 when rounded off to two significant figures. ACCURACY AND PRECISION Accuracy  refers to the nearness of a value to the true or actual value.  measured by percentage error Error – the difference between a measured value and the true (or most probable) value. % error = /Average value – True value/ x 100% True value Higher % error, less accurate Precision  indication of the agreement among different measurements of the same event.  measured by deviation Deviation – absolute value of the difference of the measured value from the average value Deviation = /Measured value – Average value/ Higher deviation, less precise MATTER Matter- anything that has mass, takes up space (volume) and possesses inertia Matter Pure substances Mixture Element Compounds Homogeneo Heterogeneo s us us (Solution) Pure Substance- homogeneous matter that cannot be separated into its components by physical means; with fixed composition and distinct properties Types of Pure Substances: 19 a. Elements- pure substance composed only of 1 type of atom; cannot be decomposed by ordinary means into simpler substances (Ex. H, He, Au, W) b. Compounds- two or more elements chemically combined in a definite and constant proportion (Ex. KCl, CH3COOH, MgCl2) Ionic Compounds Structural units are the cations and anions In the solid state, the ions do not move from their positions in the lattice but only vibrate in place Properties of Ionic Compounds Melting Point: High Electrical Conductivity: Solid Non-conducting Molten Conducting Aqueous Conducting Hardness: Very Hard Malleability: Brittle Covalent Molecular Substances Uncharged or neutral structural units (molecules) in the crystal lattice. The atoms in each molecule are held together by strong COVALENT BONDS. Properties of Covalent Molecular Compounds Melting Point: Low Electrical Conductivity: Solid Non-conducting Molten Non-conducting Aqueous Non-conducting Hardness: Soft Malleability: Brittle Covalent Network Substances The structural units that occupy the lattice points in the solid are ATOMS. The atoms are bound to each other by strong COVALENT BONDS. Properties of Covalent Network Substances Melting Point: Very high Electrical Conductivity: Solid Non-conducting (except graphite) Molten Non-conducting Aqueous Insoluble Hardness: Very Hard Malleability: Brittle Mixture- combination of different substances in variable proportions; can be separated into its components by physical methods of separation Types of Mixtures: a. Homogeneous- uniform composition and properties throughout a given sample, but composition and properties may vary from one sample to another (e. g. solutions) b. Heterogeneous- with non-uniform properties throughout a sample where components retain their identity and phase boundaries exist (e.g. colloids, suspensions) Other Classification of Matter a. Physical States of Matter (Phases of Matter) SOLID – rigid, has definite volume and shape LIQUID – fluid ( has ability to flow), takes the shape of the portion of the container they occupy GAS – fluid, expands to fill up its container 20 b. Special forms based on arrangement of particles and the degree of cohesiveness Crystalline solids; amorphous solids; liquid crystals Crystalline solids – high degree of cohesiveness and very orderly arrangement of particles Amorphous/non-crystalline solids – disordered arrangement of particles but with a high degree of cohesiveness Liquid crystals – medium degree of cohesiveness and very orderly arrangement of particles; allows a degree of ordered motion of particles PROPERTIES OF MATTER Properties of Matter Extensiv Intensive Physical Chemical e/Extrinsi / Intrinsic c Extensive Properties properties that depend on the amount of material observed e.g. mass, volume, texture Intensive Properties properties that does not depend on the amount of material observed e.g. density, odor, taste Extrinsic Properties properties that can vary with different samples of the same material e.g mass, volume, size Intrinsic Properties properties which are inherent to the substance and do not change for different samples of the same substance e.g. density, boiling and melting points, odor, taste Physical properties characteristics observed or measured without changing the identity or composition of the material Chemical Properties characteristics observed or measured only by changing the identity or composition of the material; ability or inability of matter to undergo a change in its identity or composition at given conditions Changes in Matter Changes in Matter Physical Change Chemical Change Phase Change Synthes Decompositio Single is n Displaceme nt Solid Liquid Gas Double Displacemen t Physical Change changes in the phase or state of a substance but not its composition e.g. changes in state (liquid  gas), shape or size (granules  powder) Phase Change – determined by existing conditions of temperature and pressure 21  Sublimation Solid to Gas Deposition Gas to Solid Melting Solid to Liquid Freezing Liquid to Solid Evaporation Liquid to Gas Condensation Gas to Liquid Chemical Change substances are converted into other substances e.g. rusting of iron, burning of wood Types of Chemical Reactions 1. SYNTHESIS / COMBINATION – formation of a bigger compound from simpler ones A+B+C…D 2. DECOMPOSITION - A single compound is broken down to 2 or more simpler substances - Solids require heat () AB+C+D+… 3. Single Displacement- Cation or anion is replaced by an uncombined element AB + C  AC + B 4. Double Displacement – Metathesis Exchange of partners AB + CD  AD + CB Other types:  Combustion - Reaction with O 2 to form CO2, H2O, N2 and oxides of any other elements present  Precipitation - Formation of a precipitate when a solution is added to another Precipitate – an insoluble or slightly soluble solid that forms when 2 solutions are mixed. Solubility Rules 1. All nitrates are soluble. 2. All acetates are soluble. 3. All NH4+ salts are soluble. 4. All salts of Group 1 are soluble. 5. All chlorides are soluble except chlorides of Hg22+, Pb2+ and Ag+. 6. All bromides are soluble except bromides of Hg22+, Pb2+ and Ag+. 7. All iodides are soluble except iodides of Hg2+, Hg22+, Pb2+ and Ag+ 8. Most sulfates are soluble except Group 2, Pb2+ and Hg2+. 9. All phosphates are insoluble except NH4+ and Group 1. 10. All chromates are insoluble except NH4+ and Group 1.  Neutralization - Reaction between an acid and a base forming water and salt LAWS OF CHEMICAL COMBINATION 1. Law of Conservation of Mass Antoine Lavoisier (1743-1794) - “Father of Chemistry” Established chemistry as a quantitative science Studied combustion “In a chemical reaction, the total mass of the starting materials (reactants) is equal to the total mass of the materials produced (products).” 2. Law of Definite Proportion or Composition Joseph Proust (1754-1826) Showed that copper carbonate always has the ff. proportion by mass: 5.3 parts Cu : 4 parts O : 1 part C “Any sample of a pure chemical substance contains the same elements in the same definite proportion by mass of its elements.” 3. Law of Multiple Proportion John Dalton (1766-1844) 22 “In different compounds of the same elements, the different masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.” HISTORICAL DEVELOPMENT OF ATOM Greeks (400 BC) o Matter was composed of 4 fundamental substances: FIRE, EARTH, WATER, AIR Leucippus and Democritus (5th BC) o First to propose that matter is made up of tiny indivisible particles called “atomos” meaning indivisible Lucretius and the Greeks (1 BC) o What appears as a solid object may actually consist of small particles o There must be some limit to the number of subdivisions which can be formed on any bit of matter o Matter can be resolved ultimately into a unit which is indivisible and indestructible “ATOM” means cannot be cut/destroyed - The Greeks were only concerned on the existence of the atom but not on its nature DALTON’S ATOMIC THEORY John Dalton (1766-1844) In 1808, published the book “A New System of Chemical Philosophy” wherein he presented the atomic theory in detail. Dalton’s Billiard Ball Model The atom is a tiny, hard, indestructible sphere. Dalton’s Atomic Theory 1. Matter consists of tiny particles called atoms which are indestructible. 2. All atoms in a given element are identical and have the same mass. 3. Atoms of different elements have different properties. 4. Reactions involve only the rearrangement of atoms; separation or union. When atoms combine to form compounds, the ratio of the no. of combining atoms is fixed. Thompson’s Raisin Bread/ Plum Pudding Model Joseph John Thomson (1904) Studied cathode ray tubes  The cathode rays are repelled by the negative pole of a magnetic field  This suggests that the ray consists of a stream of negatively charged particles  All atoms must contain electrons. 23   An atom is a diffuse, spherical cloud of positive electrification with randomly embedded negatively charged electrons.  Thomson measured the charge to mass ratio of the electron: e/m = -1.76 x 108 c/g  He also showed that whatever metal is used as a cathode and whatever gas is present inside the tube, the cathode ray consist of the same particles as shown by the same e/m ratio. Importance of Thomson’s Experiment  It correctly suggested that the atom consists of an arrangement of + and – charges.  It postulated the presence of the electron in all matter Robert Millikan (1909) Using oil drop experiments, he determined the charge of an electron: -1.6 x 10-19 c Thus the mass of an electron is (using e/m ratio): 9.11 x 10-28 g Rutherford’s Nuclear Atom Model (Alpha Scattering Experiment) Ernest Rutherford (1871-1937) and Hans Geiger (1882-1945)  Majority were undeflected  Some were slightly deflected  Few bounced off Explanations:  Most of the mass and all the (+) charges on an atom are centered in a very small region called the nucleus.  The atom is mostly empty space.  The magnitude of (+) charge is different for different atoms.  Electrons move around the (+) nucleus. 24 Eugene Goldstein (1850-1930)  Goldstein, in 1886 identified the positively charged particle and named it proton  He used cathode with holes and observed rays passing through the holes opposite in direction to those of the cathode rays.  The mass of this particle almost the same as the mass of the H atom  The charge is equal in magnitude (but opposite in sign to that of the electron) Bohr’s Solar System Model of the Atom Neils Bohr (1885-1962) In 1913, tried to explain the line spectra of hydrogen Features: The electrons move about the nucleus in certain circular orbits. Only certain orbits and energies are allowed. The electron can remain in an orbit indefinitely. In the presence of radiant energy, the electron may absorb E and move to an orbit with higher E Quantum or Wave-Mechanical Model Louis de Broglie (1892-1987), Erwin Schrodinger (1887-1961), Werner Heisenberg (1879-1976) Features: The energy of the electron is quantized. The electron moves in 3-D space around the nucleus but not in an orbit of definite radius. The position of the electron cannot be defined exactly, only the probability. Heisenberg Uncertainty Principle There is a fundamental limitation to just how precisely we can know both the position and the momentum of a particle at a given time. The Nature of Light - Radiant energy that exhibits wavelike behavior and travels through space at the speed of light in a vacuum. It has oscillating magnetic and electric fields in planes perpendicular to each other. Primary Characteristics of Wave 1. WAVELENGTH, λ - distance between two consecutive peaks or troughs in a wave 2. FREQUENCY, - number of waves or cycles per second that pass a given point in space Relationship of λ and λ  1/ν or λν = c Where c= speed of light (2.9979 x 108 m/s) Atomic Spectra - The spectra produced by certain gaseous substances consist of only a limited number of colored lines with dark spaces between them. - This discontinuous spectra. - Each element has its own distinctive line spectrum- a kind of atomic fingerprint. Robert Bunsen (1811-1899) and Gustav Kirchhoff (1824-1887) Developed the first spectroscope and used it to identify elements. 25 Max Planck (1858-1947) Explained certain aspects of blackbody radiation Blackbody – any object that is a perfect emitter and a perfect absorber of radiation Sun and earth’s surface behave approximately as blackbodies Proposed that energy, like matter, is discontinuous. When the energy increases from one allowed value to the next, it increases by a tiny jump or quantum. Matter could absorb or emit energy only in the whole number multiples of the quantity. E=hv where E is energy h is Planck’s constant = 6.626 x 10-34 Js v is frequency So, ΔE = n hv Where n is an integer (1,2,3…)  Energy is “quantized” and can only occur in discrete units of size hv (packets of energy called Quantum)  Transfer of energy can only occur in whole quanta, thus, energy seems to have particulate properties. Albert Einsetein (1879-1955) Proposed that electromagnetic radiation is itself quantized Electromagnetic radiation can be viewed as a stream of particles called PHOTONS Summary of the Works of Einstein and Plancks Energy is quantized. It can occur only in discrete units called quanta. Electromagnetic radiation, which was previously thought to exhibit only wave properties, also exhibit particulate properties, thus the dual nature of light. If light has particulate properties, not just wave, does matter also have wave properties, not just particulate? Louis de Broglie (1892-1987) Small particles of matter may at times display wavelike properties. For a particle with velocity, v m=h/λv Then λ = h / mv Thus, we can calculate the wavelength for a particle. All matter exhibits both particulate and wave properties. Large pieces of matter predominantly exhibit particulate properties because their λ is so small that it is not observable. Very small pieces of matter such as photons exhibit predominantly wave properties. Those with intermediate mass, such as electrons, show clearly both particulate and wave properties. MODERN VIEW OF THE ATOM ALLOTROPE – elements with different forms (composed of one type of element) ISOTOPES – elements with different mass number due to the difference in the number of neutrons ISOBARS – different elements with the same mass number but different atomic number Atom and the subatomic particles The diameter of an atom is in the order of 10-8 cm The nucleus is roughly 10-13 cm in diameter (1/100,000 diameter of the atom) The charge of the nucleus is a unique character of the atoms of an element The charge is positive 26 Particles within the nucleus PROTON Eugene Goldstein (1886) from Greek “protos” meaning “first” mass of p+ = 1.67 x 10-24 g charge = +1.60 x 10-19 c The no. of p+ is a unique property of an element # of p+ = atomic #, Z = nuclear charge = # of e -s in a neutral atom NEUTRON James Chadwick (1932) Protons cannot account for the total mass of the atom Has the same mass as the proton but has no charge Symbol: n0 mass of p+ + mass of n0 = mass of atom (atomic mass) # of p+ + # of n0 = mass #, A A = Z + # of n0 ELECTRON Ernest Rutherford negatively charged in a neutral atom :  # of e - = # of p+ = Z Summary: Particle Discovery Mass in grams Charge Electron discovered by JJ Thomson; name given by George 9.11 x 10-28 -1 Stoney Proton discovered by Rutherford in 1911, name given by 1.67 x 10-24 +1 Goldstein Neutron discovered and named by James Chadwick, 1932 1.67 x 10-24 0 Symbol of the Atom Atomic number, Z, is the number of protons in the nucleus Ex. The element N has 7 protons, so Z= 7. Mass number, A, is the sum of the number of protons and neutrons in the nucleus of an atom Ex. An atom with 5 protons and 5 neutrons has an atomic number of 5 and a mass number of 10 ISOTOPES Francis William Astron (1877-1945) – observed using the mass spectrometer that neon has 3 isotopes The listed atomic mass of an element is the weighted average of the atomic masses of the naturally occurring isotopes. Atomic mass =  (% abundance)(isotopic mass) For Ions (+) charge – cation - Lost electrons equal to the charge (-) charge – anion - Gained electrons equal to the charge 27 NUCLEAR CHEMISTRY - proposed by Marie Curie (1867-1934) Spontaneous disintegration of an unstable atomic nucleus with accompanying emission of radiation in order to form a more stable species. Nuclear Equation The sum of the mass #’s (A) must be the same on both sides The sum of atomic #’s (Z) must be the same on both sides Nuclide A nucleus with a specified mass # (A), # of p+ (Z) and # of n0 Stable nuclide Radioactive nuclide Stability of Nuclide ODD-EVEN RULE Even # of n0 and p+ : more likely to be stable Odd # of n0 and p+ : more likely to be unstable MAGIC NUMBER Isotopes with specific # of p+ or n0 are more stable than the rest: 2, 8, 20, 28, 50, 82 and 126 All nuclides with 84 or more protons are radioactive. e. g. Po, At …. TYPES OF RADIOACTIVE DECAY 1. ALPHA DECAY OR EMISSION - particle: Heavy, travel short distances Usually emitted by a heavy nuclei 2. BETA DECAY OR EMISSION OR NEGATRON EMISSION  particle (negatron) Usually when neutrons are in excess, they are transformed into protons with emission of beta particles. 3. POSITRON EMISSION Usually when p+ are in excess, these are transformed into n0 with emission of positron 4. ELECTRON CAPTURE OR K- CAPTURE Usually happens when p+ are in excess (as in positron emission) Nuclear stability achieved by capturing one of the inner e -s (lowest E level or K- shell) converting a p+ to a n0 X-rays emitted 5. GAMMA EMISSION ( – radiation is emitted) high energy photons or radiation similar to x-rays but shorter  , high , high penetration no mass, A and Z of nucleus remain unchanged 28 NUCLEAR FISSION Heavy nucleus splits into 2 or more lighter nuclei Occurs when a heavy nucleus is struck with projectiles or bullets (nuclear particles) NUCLEAR FUSION Nuclei of lighter elements are made to combine to form heavier nuclei Occurs at very high temp. More E released but difficult to harness HALF-LIFE, t1/2 Time required for half of radioactive nuclei in a sample to undergo radioactive decay Constant for every radioactive isotope t1/2 = ln 2/ k k is the rate ln (N/N0) = -kt N0 = initial amount or activity N = amount left or activity left after time t THE ELUSIVE ELECTRON Quantum Number – describes the orbital and the electron ORBITAL is an energy state for an electron described by the three quantum numbers n, l and m l - may hold two electrons with opposite spins 1. Principal Quantum Number (n) Take positive, nonzero integral values: 1,2,3… Main energy level or principal shell As n increases: orbital becomes larger, e- becomes farther from the nucleus higher E- e- is less tightly bound to the nucleus 2. Azimuthal or Angular Momentum Quantum Number (l) Values: 0 to n-1 for each value of n Sublevel or subshell Related to the shape of the orbital Orbital Symbol - combination of n and l l Letter - consists of a number (for n) and a letter (for l) designation e.g. 3s  n = 3 ; l is s = 0 0 s 1 p 3. Magnetic Quantum Number (ml) 2 d Values: l to –l including zero 3 f Related to the orientation in space of the angular momentum associated with the orbital Degenerate orbitals – orbitals having the same energies 29  e.g. the three p-orbitals have the same energy 4. Electron Spin Quantum Number (ms) Values: +1/2, -1/2 The value does not depend on any of the three quantum numbers Pauli Exclusion Principle (Wolfgang Pauli 1900 -1958) - In a given atom, no 2 e-’s can have the same set of 4 q.nos. Thus, an orbital can hold only 2 e-’s, and they must have opposite spins. Electronic Configuration – describes the manner in which electrons are arranged in an atom Ground state electronic configuration- lowest energy arrangement of electrons Excited state- allowed arrangements of electrons other than the ground state Isoelectronic- same number of electrons Rules to remember when writing ground state electronic configurations ¤ Aufbau Principle- the orbitals of an atom are filled in order of increasing energy - According to the (n+l) rule. The lower the value of (n+l), the lower the energy of the orbital. If the (n+l) values of two orbitals are the same, the one with lower n is filled first. ¤ Hund’s Rule of Multiplicity- the lowest energy arrangement of electrons in a set of degenerate orbitals is where there is a maximum number of electrons of the same spin. Electrons occupy degenerate orbitals singly before pairing. THE PERIODIC TABLE The Elements  there are 112 elements to date, 90 of which are naturally occurring Early Classifications 1. Johann Wolfgang Dobereiner’s Law of Triads (1817) - In a triad , the combining weight of the central member is the average of its partners. 2. John Newlands’ Law of Octaves (1865) - When elements are arranged in increasing atomic mass, every eighth element had similar properties. Shortcomings: Some positions were forced just to maintain his proposition Some positions contained 2 elements There were no room for other elements which may be discovered 3. Julius Lothar Meyer’s Atomic Volume Curve and Periodic Table (1869) A periodic trend in properties is observed when elements are arranged in increasing atomic weights. 4. Dmitri Mendeleev’s Periodic Table and Periodic Law (1869) Properties of elements are periodic functions of their atomic weights 30  Predicted the discovery of 10 elements The Modern Periodic Law - The properties of the elements are functions of their atomic numbers Groups Vertical rows Previous notation: IA – VIIIA, IB – VIII New IUPAC* notation: 1-18 *IUPAC – International Union of Pure and Applied Chemistry Elements belonging to the same group have similar (not identical) properties Special names of some groups Group 1 – Alkali metals Group 2 – Alkaline earth metals Group 17 – Halogens Group 18 – Noble Gases Periods Horizontal rows Properties of elements that belong to a period show a pattern or trend that is repeated in the next period Numbered 1-7 Pattern in Ion Formation Most elements form ions (except noble gases) Group 1 : +1 Group 15 : -3 Group 2 : +2 Group 16 : -2 Group 13 : +3 Group 17 : -1 Group 14 : do not readily form ions Of the known elements, 11are gases at room temperature. four are liquids at 25°C, Hg, Br, Ga and Cs. If Fr can be prepared in large quantities, it is expected to be a liquid. Property Across a period (left to right) Down a group (top to bottom) atomic size/radius Decreasing Increasing ionization energy Increasing Decreasing affinity for electrons Increasing (upto Group 17) Decreasing Tendency to form Decreasing Increasing Cation Tendency to form Increasing (upto Group 17) Decreasing Anion Metallic Character Decreasing Increasing Electronegativity Increasing Decreasing Note: The size of the cation is smaller as compared to its neutral atom The size of the anion is larger as compared to its neutral atom. Atomic Size ► Covalent radius – ½ the distance between the nuclei of two identical atoms joined by a single covalent bond. ► Metallic radius – ½ the distance between the nuclei of 2 atoms in contact in the crystalline solid metal. Ionization Energy ► Energy required to remove an e- from a gaseous atom or ion X(g) X+(g) + e- Where the atom or ion is assumed to be in its ground state Affinity for electrons 31  ► Tendency of an atom or ion to attract additional e- X(g) + e- X- (g) Electronegativity ► The attraction of an atom for shared electrons. Note: Metals react with oxygen gas forming a basic oxide in water. Nonmetals react with oxygen gas forming an acidic oxide in water. CHEMICAL LANGUAGE AND SHORTHAND Chemical symbols An element is represented by a symbol which may be one or two letters; the first is capitalized and the second is in the lower case. The symbols may be derived from the Greek, German or Latin names of the elements. Binary Covalent Compounds Binary covalent compounds are formed between two non-metals A. Naming binary covalent compounds 1. Identify the elements present in the compound given by the chemical formula. The name of the more metallic element is written first. 2. Change the suffix of the less metallic element to –ide. 3. Use the prefix corresponding to the number of atoms present in the compound. Number Greek Prefix Number Greek Prefix 1 Mono- 6 Hexa- 2 Di- 7 Hepta- 3 Tri- 8 Octa- 4 Tetra- 9 Nona- 5 Penta 10 Deca- The mono- prefix is frequently omitted, particularly for well-known substances. If no prefix is use, it usually implies that no number of atoms of element is one. However, experts in nomenclature caution that this can be dangerous and suggest that it is better to include the mono- prefix. Some compounds are known only by their common names. The most common of this are: Forrmula H2O NH3 PH3 Name Water Ammonia Phosphate. Writing formulas of binary compounds 1. Represent each kind of element in a compound with the correct symbol of element. 2. Indicate by a subscript the number of atoms of each element in a molecule of the compound. 3. Write the symbol of the more metallic element first. (H is an exception to this rule.) IONIC COMPOUNDS Compounds formed between metals and nonmetals are called ionic compounds. A. Naming Ionic Compound 1. Write the name of the cation first, followed by the name of the anion. 2. Unlike binary covalent compounds, PREFIXES ARE NOT USE to indicate the number of ions present in the formula. 32  Note that for ionic compounds, the prefixes are not attached to the chemical name to denote the number of atoms of the elements. The number of atoms is implied by the charges of the cation and the anion. It is therefore important to know the charges of the common cations and anions. 3. Most transition metals can exist in more than one ionic form. Thus, it is important to know the charge of the cations in their compounds. Examples: Formula Stock system Old system SnCl4 tin (IV) chloride stannic chloride SnBr2 tin (II) bromide stannous bromide The method of indicating the charge of the cation involves placing a Roman numeral equivalent to the magnitude of the charge of the cation in parenthesis after the English name is called the Stock System of Nomenclature. Some ionic compounds form crystals that contain a certain proportion of water molecules apart from the ions of the compound. Such compounds are called HYDRATES. Hydrates are named just like other ionic compounds except for the addition of the “hydrate” with a Greek prefix indicating the number of water molecules per unit of the ionic compound. Example: CuSO45H2O copper (II) sulfate pentahydrate or cupric sulfate pentahydrate B. Writing Formulas of Ionic Compounds 1. Write the symbol of the positive ion (cation) first, followed by the symbol of the negative ion (anion). 2. Write the charge of each ion over the symbol of that ion. Usually, for the main group elements, the group number usually gives the charge of the monoatomic ion. Remember that Group 1 elements would have a charge of (+1); Group 2 (+2); Group 3 (+3); Group 16 (-2); Group 17 (-1); and Group 18 (0) unless indicated. 3. Choose a subscript that will make the net charge zero. The simplest procedure is to use the absolute value of the charge of the anion as the subscript for the cation; and the absolute value of the cation charge as the subscript for the anion (CROSS-OVER RULE). When both subscripts in the formula can be divided by same number to simplify the formula, you should do so, unless you know the actual molecule represented. 4. For hydrates, follow the same steps, then add a centered dot, followed by the number of water molecules (indicated by the prefix) and the chemical formula of water. ACIDS A. Naming Binary Acids Binary acids contain only two different elements- hydrogen and a nonmetal. Binary acids are named as hydro ____ic acid, where the stem of the nonmetal is inserted in place of the line. Thus, HF- hydrofluoric acid and HBr- hydrobromic acid The names hydrogen fluoride and hydrogen bromide are also used for HF and HBr, respectively. Both names are correct although the convention is that these compounds are named as acids when they are present in aqueous solutions. Thus, HF in aqueous solution is hydrofluoric acid, but pure HF is referred to as hydrogen fluoride. B. Naming Oxyacids Another type of acid is the oxyacids derived from the oxyanions. Since some elements form more than one oxyanion, they also form more than one oxyacid. The name of the oxyacid is derived from the name of the oxyanion with a change in the suffix using the following rules: 1. If the name of the oxyanion ends in –ate, the name of the oxyacid will be of the form ____ic acid. 33  Example SO42- sulfate H2SO4 sulfuric acid ClO4- perchlorate HClO4 perchloric acid 2. If the name of the oxyanion ends in –ite, the name of the oxyacid will be of the form ___ ous acid. Example SO32- sulfite H2SO3 sulfurous acid ClO- hypochlorite HClO hypochlorous acid Names and Symbols of Some Common Polyatomic Anions Formula Name Formula Name OH- Hydroxide NO3- Nitrate 2- O2 Peroxide NO2- Nitrite - CN Cyanide CH3COO- Acetate - N3 Azide CrO42- Chromate 2- SO4 Sulfate Cr2O72- Dichromate 2- SO3 Sulfite MnO4- Permanganate - HSO4 Hydrogen sulfate or C2O42- Oxalate bisulfate HSO3- Hydrogen sulfite or SCN- Thiocyanate bisulfite PO43- Phosphate CO32- Carbonate 2- HPO4 Hydrogen phosphate HCO3- Hydrogen carbonate or H2PO4 - Dihydrogen phosphate bicarbonate Some common oxyanions Chlorine Bromine ClO4- Perchlorate BrO4- Perbromate - ClO3 Chlorate BrO3- Bromate - ClO2 Chlorite BrO2- Bromite - ClO Hypochlorite BrO- Hypobromite STOICHIOMETRY Chemical Reactions Processes in which substances are changed into one or more new substances Represented by chemical equations: Reactants  Products 2H2 + 1 O2  2H2O 2 molecules + 1 molecule  2 molecules 2 moles + 1 mole  2 moles 34  4.04 g + 32.00 g  36.04 g 36.04 g reactants  36.04 g products FOLLOWS THE LAW OF CONSERVATION OF MASS Balancing Chemical Equations Some important points: Use correct chemical formulas Adjust only the coefficients, NOT the subscripts Balance elemental forms ( e.g. Ar, Cu, Na, O2, N2, I2, S8…) and H and O last. Use the simplest possible set of whole no. coefficients Stoichiometry- The quantitative study of reactants and products in a chemical reaction Mole Method - The stoichiometric coefficients in a chemical equation can be interpreted as the number of moles of each substance. Steps: Write correct chemical formulas and balance the equation. Convert the quantities into moles. Use the mole ratios to calculate moles of the required substance. Convert calculated moles to whatever units required. Three types of calculation: he Mole In 1971, at the 14th meeting of the General Conference of Weights and Measures, scientists agreed to adopt the mole as the unit of an amount of substance The mole (abbreviated mol) is the amount of substance that contains the same number of elementary particles as the number of atoms in exactly 12 grams of C-12. Ways of expressing the mole: 1. by number of particles (use Avogrado’s number, 6.02 x 10 23 particles per mole) 2. by mass (use molar mass) 3. by volume (use molar volume, 22.4 L at STP) Interconversions ÷ MM x 6.02 x 1023 Mass Mole No. of particles x MM ÷ 6.02 x 1023 35 The molar mass is the mass in grams of 1 mole of a substance. The molar mass is numerically equal to the atomic mass (or atomic weight) of an atom or the formula mass of a molecule, a compound or a polyatomic ion. Formula and Composition The percentage composition of a compound is a list of the percentages by weight of the elements in the compound. The percentage by weight of an element in a compound is numerically equal to the number of grams of the element that are present in 100 g of the compound Ex. What is the percentage composition of quick lime, CaO? Ans. 71.5% Ca, 28.5% O Empirical Formula- is the formula with lowest possible whole number subscripts to represent the composition of the compound. It can be determined from the % composition data. Ex. Barium carbonate, a white powder used in paints, enamels and ceramic, has the following composition: Ba, 69.58%; C, 6.090% and O, 24.03%. Determine its empirical formula Ans. BaCO3 Molecular Formula- gives the actual composition or the actual number of atoms of each element present in one molecule or one formula unit of the compound Ex. Molecular formula of glucose: C6H12O6 Empirical Formula of glucose: CH2O Stoichiometry of Reactions Chemical Stoichiometry- is the quantitative relationship of the amounts of reactants used and amounts of products formed in a reaction. This mass relationship is expressed in the balanced equation for the reaction. Percent yield- portion of the theoretical yield of product that is actually obtained in the reaction %yield= (actual amt of product obtained/ theoretical amt) x 100 Theoretical Yield - the amount of product that would result if all the LR reacted. - Maximum obtainable yield Actual Yield - The amount of product actually obtained from a reaction - Always less than theoretical yield Limiting reactant- reactant that is completely consumed in the reaction. It also determines the amount of products that can be formed. Excess reactant- reactant that is not completely used up in a chemical reaction TIES THAT CHEMISTRY BIND Chemical Bonds- net forces of attractions that hold atoms together Properties: Bond energy – amount of energy that must be supplied to separate the atoms that make a bond Bond length – distance between 2 nuclei of 2 covalently bonded atoms Bond order – number of bonds between atoms Types of Chemical Bonds a. covalent bond- pair of electrons that is shared by two atoms of nonmetals; represented by Lewis structure or electron dot formula 36  Types of Covalent Bonds: Single bond - two atoms held by one e- pair Double bond – two atoms held by 2 e- pairs Triple bond – two atoms held by 3 e- pairs Higher Bond order, shorter Bond length, higher Bond energy Polar covalent bond – one atom is more electronegative than the other atom; unequal sharing of electrons; the more electronegative atom is partially negative and the less electronegative atom is partially positive. Nonpolar covalent bond – equal sharing of electrons Coordinate Covalent Bond – the electrons being shared comes from a single atom b. ionic bond or electrovalent bond– It is the transefer of electrons from a metal to a nonmetal, i.e., the metal loses an electron while the nonmetal gains an electron converting them intro charged ions. - attraction between cations and anions c. metallic bond- the attraction between the cations in the lattice and the “sea of delocalized electrons” moving within the lattice Lewis Structure-one or a combination of Lewis symbols to represent a single atom (neutral or charged), a molecule or a polyatomic ion. - based on Octet Rule Octet rule- the observed tendency of atoms of the main block elements to lose, gain or share electrons in order to acquire an octet of electrons in their outermost main energy level It is more appropriately called Noble Gas Rule Electron Pairs could either be Lone pairs – pairs of electrons localized on an atom Bonding pairs – those found in the space between the atoms Drawing Lewis Structures 1. Sum the valence electrons from all atoms (total # of e-’s) Total electrons = sum of the valence electrons of all atoms – charge 2. Determine the central atom and draw the skeletal structure. Cental atom is the most metallic atom or the least electronegative. 3. Use a pair of e-’s to form a bond between each pair of bound atoms. 4. Distribute remaining electrons to the terminal atoms to satisfy octet. 5. If there are still available electrons, put them on the central atom to satisfy octet. 6. If the central atom does n