Science 9 Unit 6 Chemical Bonding Study Guide PDF

Unit 6 Chemical Bonding Table of Contents Table of Contents 1 Chemical Bonding 3 Essential Questions 4 Review...

Unit 6 Chemical Bonding Table of Contents Table of Contents 1 Chemical Bonding 3 Essential Questions 4 Review 4 Lesson 6.1: Chemical Bonds and the Laws on Chemical Bonding 5 Objectives 5 Warm-Up 5 Learn about It 6 Key Points 11 Web Links 12 Check Your Understanding 12 Challenge Yourself 13 Lesson 6.2: Lewis Electron-Dot Symbol and the Octet Rule 15 Objectives 15 Warm-Up 15 Learn about It 16 Worked Examples 19 Key Points 21 Web Links 22 Check Your Understanding 22 Laboratory Activity 24 Performance Task 26 Self Check 28 Key Words 28 Wrap Up 29 References 29 Answer Key 30 2 GRADE 9 | SCIENCE Unit 6 Chemical Bonding There are only 118 known elements in the periodic table but the range of substances that exist in nature extends beyond these 118 elements. To form the different substances we encounter in nature, the atoms of the elements bond together in multiple ways. For example, an oxygen molecule (O2) can react with two hydrogen molecules (H2) to form two water molecules (H2O). In normal atmospheric conditions, O2 and H2 molecules are gases while H2O molecules are liquid. The properties of substances depend on the type of chemical bonds that hold their atoms together. A similar reaction with H2 and O2 molecules can produce substances other than water. When one O2 molecule reacts with one H2 molecule, one molecule of hydrogen peroxide (H2O2) is produced. Even though H2O2 and H2O are composed only of hydrogen and oxygen atoms, they are two different compounds. Different products result when the proportion of the reactants are varied. What determines the type of chemical bonds present in each substance? In this unit, you will learn about the basic laws of chemical bonding, and how elements form bonds together to create different compounds. 3  Essential Questions At the end of this unit, you should be able to answer the following questions. How do we describe chemical bonding in different substances? What are the laws governing chemical bonding? How is hydrogen peroxide and water different from one another? Review Matter can undergo either physical or chemical change. ○ A substance undergoes physical change when it changes its physical appearance but not its chemical composition. Examples of physical changes are state changes such as freezing, evaporation, and sublimation. ○ A substance undergoes chemical change when it is transformed into a new substance. This process is usually accompanied by one or more pieces of evidence such as change in color, evolution of heat, production of gas, or formation of a precipitate. An element is composed of only one kind of atom. It is the simplest form of pure substance. Some elements exist as single atoms while some exist as molecules. When two or more elements chemically combine, they form a compound. A compound has a fixed proportion by mass and has a different chemical property compared to the elements that constitute it. The periodic table is a systematic and organized way of presenting elements. It arranges the elements in order of increasing atomic number and recurring chemical properties. The columns in the periodic table are called groups (or families) while the rows are called periods. Elements belonging to the same group have similar chemical properties. The electrons found on the outermost energy level are called valence electrons. These specific types of electrons are directly involved in chemical reactions. 4  Lesson 6.1: Chemical Bonds and the Laws on Chemical Bonding Objectives In this lesson, you should be able to: describe chemical bonding in terms of attractive and repulsive forces; and enumerate physical laws that govern chemical bonding and formation of substances. Substances exist due to the interaction of their constituent atoms. From the food that you eat and the water that you drink, they all contain a group of atoms that are bound together. The type of bond they form depends on the atoms themselves. More so, the type of bond predicts how the product behaves and reacts with other products. Chemical bonding and the formation of substances are governed by physical laws which will be discussed in this lesson. How do atoms interact with other atoms to form substances? Warm-Up Attraction or Repulsion? In this activity, you will be observing how a magnet behaves at different distances. Materials: two bar magnets (or two horseshoe magnets) Procedure: 1. Form a group of three. Secure two magnets from your teacher. Then, follow the steps below. Look at the magnets while following the next steps. 2. Stand up and hold the positive end of one of the magnets. Let one of your 5  groupmate hold the positive end of the other magnet and stand meter away from you. What do you feel? Record your observations. 3. Move one foot forward and observe if you feel anything about the magnet. Continue moving until you can feel a force acting on to the magnet. How will you describe the force? Record your observations. 4. Continue moving until you and your classmate are 1 foot apart. Record your observations below. 5. After the activity, return the magnets to your teacher. Learn about It Chemical Bonds There are only 118 elements in the periodic table, but of course, the substances in nature outnumber 118. Atoms chemically react with one another to form chemical bonds and the multitude of substances we see in nature. A chemical bond is a force of attraction that holds atoms together in a compound. There are different types of chemical bonds between atoms that depend on the nature of the atoms participating in the bond. Imagine two hydrogen atoms near each other. As they approach one another, three simultaneous forces act on the two atoms. These are (1) the attraction between protons and electrons, (2) the repulsion between protons, and (3) the repulsion between electrons. Fig. 1. Attractive and repulsive forces between two hydrogen atoms. 6 When atoms are very far from each other, either no interaction will occur between them or only a very negligible interaction will occur. When the atoms are very near to each other, repulsion occurs. When the atoms are at the right distance from each other, the forces of attraction and repulsion are balanced. At this point, chemical bonding takes place. Fig. 2. Chemical bonding occurs when there is a balance between attractive and repulsive forces. The interaction between atoms is also similar with the interaction of magnets. When the magnets are distant from each other, you would not feel any force. Both attraction and repulsion are negligible. However, when the distance between the two magnets becomes narrower, the forces of attraction and repulsion become significant. The point before there is a significant repulsion between the two magnets is the point where chemical bonding occurs. 7  Fig. 3. The balance between attractive and repulsive forces in a magnet. When atoms bond together, their valence electrons participate in the formation of chemical bonds. Valence electrons are the outermost electrons of an atom. When atoms of other groups react with other atoms, they do so to reduce their chemical energy and achieve stability. Bonding lowers the potential energy between positively and negatively charged particles. The formation of chemical bonds follows physical laws. These include the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. Law of Conservation of Mass The law of conservation of mass states that mass can neither be created nor destroyed. When chemical reactions happen, the total mass of the reactants should be equal to the total mass of the products. It 8 was demonstrated by Antoine Lavoisier, the father of chemistry. For example, if 4.00 grams of hydrogen combine with 32.00 grams of oxygen, the product should be 36.00 grams of water. Fig. 3. Formation of water from hydrogen and oxygen. Law of Definite Proportions A molecule of carbon dioxide (CO2) contains one atom of carbon and two atoms of oxygen. Whatever amount of carbon dioxide you have, the composition of carbon dioxide is always the same. The composition is not affected by the source of the substances used to synthesize it. This is explained by the law of definite proportions which states that a substance, regardless of amount and origin, should have a fixed composition of its constituent atoms. It was proposed by Joseph Proust in 1799. For example, carbon dioxide will always contain one carbon atom and two oxygen atoms, whether it came from your lungs or your car engine. Fig. 4. A representation of a carbon dioxide molecule. 9 Law of Multiple Proportions Atoms can sometimes bond in multiple ways to produce different substances. For example, carbon and oxygen atoms can form various substances when they combine. In the previous example, carbon can bond with two oxygen atoms to form carbon dioxide (CO2). However, carbon can also bond with only one oxygen atom to form carbon monoxide (CO). Carbon dioxide and carbon monoxide are two separate substances formed when carbon bonds with oxygen. Fig. 5. Carbon and oxygen atoms in carbon monoxide and carbon dioxide. The formation of different substances from the same set of atoms is described by the law of multiple proportions. The law states that when two elements combine with each other to form two or more compounds, the ratios of the masses of one element that combines with the fixed mass of the other are simple whole number ratios. The law was formulated by John Dalton based on his earlier theories. If we are about to compare CO and CO2, the mass of oxygen in CO2 is twice that of the mass in CO. The mass of oxygen in CO2 cannot be a fraction of the mass of oxygen in CO and vice versa. You cannot have CO1/2 or any other fraction in your chemical formula. Table 1. Demonstrating the law of multiple proportions for CO and CO2. CO: CO2 Ratio of Compound Mass of carbon Mass of oxygen mass of oxygen CO 12.01 g 16.00 g 1:2 CO2 12.01 g 32.00 g The same thing is true for water (H2O) and hydrogen peroxide (H2O2). The ratio of the masses of hydrogen to oxygen is always 2:1 for H2O and 1:1 for H2O2. The mass 10 of oxygen in H2O2 is twice that of the mass in H2O. Their masses are also only found as whole number multiples of one another. Table 2. Demonstrating the law of multiple proportions for H2O and H2O2. H2O: H2O2 Ratio of Compound Mass of hydrogen Mass of oxygen mass of oxygens H2O 2.02 g 16.00 g 1:2 H2O2 2.02 g 32.00 g Key Points A chemical bond is a force of attraction that holds atoms together in a compound. When atoms bond together, their valence electrons participate in the formation of chemical bonds. Valence electrons are the outermost electrons of an atom. The law of conservation of mass states that mass can neither be created nor destroyed. The law of definite proportions states that a substance, regardless of amount and origin, should have a fixed composition of its constituent atoms. The law of multiple proportions states that when two elements combine with each other to form two or more compounds, the ratios of the masses of one element that combines with the fixed mass of the other are simple whole number ratios. 11  Web Links For further information, you can check the following web links: Want a live action of how the law of conservation of mass was discovered? Look at a clip of the film Einstein’s Big Idea here and see how Lavoisier demonstrated Adrian Mok. 2011. ‘Antoine Lavoisier - conservation of mass.’ https://www.youtube.com/watch?v=x9iZq3ZxbO8 Watch a short experiment on how constant or definite ratios of atoms are determined Seth Furlow. 2015. ‘Law of Definite Proportions.’ https://www.youtube.com/watch?v=pR3OCuqxwwo Check Your Understanding A. Read the paragraphs below. Fill in the blanks with the correct answer. Carbon and oxygen are two of the most important elements of humanity. These atoms combine to form different compounds needed to sustain life. For example, carbon dioxide, CO2, is a gas that is needed by plants to start up photosynthesis. Carbon and oxygen atoms are held by 1. _________________. This attraction is so strong that energy is needed to break it. In a carbon dioxide molecule, the ratio of the number of carbon to the number of oxygen is always 2. ______. This ratio is the same for all molecules of CO2, regardless whether it is being exhaled by humans or it is being exhausted by vehicles. This demonstrates the 3. ___________________________. This law was formulated by 4. _____________________. When you eat sugar, your body combusts it with oxygen to produce carbon dioxide and water. The amount of sugar taken and the amount of oxygen used for combustion is equal to the total amount of carbon dioxide and water produced. Therefore, if you have eaten 45 grams of sugar, and your body used 12  up 48 g of oxygen, the total mass of the carbon dioxide and water produced is equal to 5. _____. This demonstrates the 6. _____________________, which was formulated by 7. ______________________. There are also other compounds of carbon and oxygen. Carbon monoxide, CO, is a toxic gas that is released in small amounts when burning fuels. In this compound, the ratio of carbon atoms to oxygen atoms is 8. _______. This ratio is different from CO2. Furthermore, the mass of the oxygen atom in CO2 is 9. ___________ compared to the mass of the oxygen atom in CO. This demonstrates the 10. __________________________, which was formulated by 11. _____________________. B. Identify the law in chemical bonding described in the following statements 1. Methane is always 75% carbon and 25% hydrogen. 2. When 10.0 grams of H2O dissociates, the combined masses of hydrogen and oxygen gases is 10.0 grams. 3. Oxides of nitrogen exist in two forms: nitrogen monoxide (NO) and nitrogen dioxide (NO2) 4. A pure sodium chloride (NaCl) sample obtained in Manila has the same composition as that of a pure sample from Cebu City. 5. Sulfur dioxide (SO2) can be further oxidized to form sulfur trioxide (SO3). 6. Twelve grams of carbon combines with four grams of hydrogen to form 16 grams of methane (CH4). 7. The ratio of the masses of oxygen per mass of 1 sulfur atom in SO2 and SO3 is 2:3. 8. The methane produced from the flatulence of cows and the methane in your gas tanks have the same smell. 9. A can of corned beef which weighs 250 g is processed by placing 200 g corned beef in a 50 g tin can. 10. Hot tea and iced tea tastes the same. Challenge Yourself Answer the following questions. 1. Determine the chemical formula of citric acid, if 72 grams carbon was found out to combine with 8 grams hydrogen and 112 grams oxygen. 13 2. There are claims in the market that coconut sugar is healthier than white sugar. What do you think of this claim? 3. According to the law of multiple proportions, the mass of an element Y bonding to an element X when it combines in multiple ways occurs in small whole number ratios. Why do you think it is not possible to have fractions in the ratio? 4. Seawater and tap water are both water but tastes different. Does this violate the law of definite composition? Explain briefly. 5. Solid aluminum reacts with liquid bromine to produce a white solid aluminum bromide. If 54 grams of aluminum yields 533.8 grams of aluminum bromide, how much grams of bromine reacts with 15.0 grams of aluminum. 14  Lesson 6.2: Lewis Electron-Dot Symbol and the Octet Rule Objectives In this lesson, you should be able to: draw Lewis electron-dot symbols of elements; and explain why elements lose, gain or share electrons. In the formation of a chemical bond, electrons at the outermost energy level of the atom participate in bonding. These electrons are called valence electrons. They are found in the outermost shell when an atom is drawn using Bohr’s model. How are valence electrons represented in bonding? Warm-Up Can I Get your Number? Using a periodic table, locate sodium, chlorine, and neon. Then, identify the number of valence electrons and the electron configuration of each element. Fill up the table and answer the following questions. Number of valence Element Electron configuration electrons sodium chlorine neon 15 Sodium is a very reactive metal. It explodes upon contact with water. Chlorine is a very reactive gas. It poisons the body when inhaled in large amounts. Neon, on the other hand, is unreactive. It is used as a stable component in lightings and advertising signs. Sodium and chlorine are reactive because they are unstable in their elemental form. They want to assume a stable form of their element. If neon is a stable element, how can sodium and chlorine achieve stability? Suggest possible ways wherein sodium and chlorine can achieve stability. Learn about It The Lewis Electron-Dot Symbol For main group elements, the number of valence electrons is equivalent to the group number using the CAS (Chemical Abstract Service) group number system. The Arabic numeral corresponds to the number of valence electrons. For example, hydrogen which is part of group 1A has one valence electron while carbon of group 4A has four electrons. If the IUPAC (International Union of Pure and Applied Chemistry) system is used, the number of valence electrons is shown below. Table 3. Group number systems and their respective number of valence electrons. Number of valence CAS group number IUPAC group number electron(s) 1A 1 1 2A 2 2 3A 13 3 4A 14 4 5A 15 5 6A 16 6 7A 17 7 8A 18 8 16 The valence electrons of an element are represented in a Lewis electron-dot symbol. Some other interchangeable terms with the Lewis electron-dot symbol are Lewis dot diagrams, electron dot structures, or simply Lewis symbol. It was proposed by Gilbert Lewis, an American scientist in 1911. The Lewis electron-dot symbol is composed of an element symbol and the dots around the element symbol. The element symbol represents the nucleus of the atom and the inner electrons that do not participate in bonding. The number of dots around the chemical symbol represents the number of valence electrons. For example, hydrogen has one valence electron. The Lewis electron-dot symbol is shown below. The positions of the dots around the element symbol is arbitrary as long as one electron is placed first on each side before pairing with another electron. There should only be a maximum of two dots per side of the element. Hence, an element has a maximum of 8 valence electrons. Elements in the same group have the same number of valence electrons. For example, since hydrogen and lithium are both members of group 1A, they both have one valence electron. The Lewis electron-dot symbol of other main group elements is shown below. 17  Fig. 6. Lewis electron-dot symbols of main group elements. Among the eighteen groups found in the periodic table, the noble gases (Group 18 or 8A) are known to be the most stable atoms. They are chemically inert. They do not form chemical bonds with other atoms, except in some conditions. The noble gases all have an electron configuration of ns2 np6 in their valence shells where n is the principal quantum number. This means that all their orbitals are completely filled. Since they have completely filled orbitals, they are chemically inert and stable. Notice that in the valence shell of the noble gases, all except He have 8 electrons in their valence shell. Atom Neon Argon Model Lewis electron-dot symbol Electron configuration 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 18 When atoms of other groups react with other atoms, they do so to reduce their chemical energy and achieve stability. Bonding with another atom allows the atoms in the compound to achieve the nearest noble gas configuration, containing eight electrons in their valence shell. An element must gain, lose, or share electrons to attain eight electrons in its valence shell during chemical bonding. This principle is called the octet rule. An exception to the octet rule is hydrogen and helium which follow the duet rule. Hydrogen only needs two electrons in its valence shell for bonding to occur while helium only needs two valence electrons to achieve stability. Some elements such as boron and beryllium attain stability even if they are less than an octet. There are also atoms which can have more than an octet. Examples are sulfur and phosphorus, and other elements at period 3 and above. Worked Examples Example 1 Draw the Lewis electron-dot symbol for boron. Solution Step 1 Identify the chemical symbol for boron. The symbol for boron is B. Step 2 Determine the number of valence electrons in a boron atom from its group number. Boron belongs to group 3. Hence, it has three valence electrons. 19 Step 3 Distribute the valence electrons around the chemical symbol one at a time. Pair the dots if all sides of the chemical symbols already have one electron. Let us Practice Draw the Lewis electron-dot symbol for aluminum. Example 2 Draw the Lewis electron-dot symbol for carbon. Solution Step 1 Identify the chemical symbol for carbon. The symbol for carbon is C. Step 2 Determine the number of valence electrons in a carbon atom from its group number. Carbon belongs to group 4. Hence, it has four valence electrons. Step 3 Distribute the valence electrons around the chemical symbol one at a time. Pair the dots if all sides of the chemical symbols already have one electron. 20  Let us Practice Draw the Lewis electron-dot symbol for silicon. Example 3 Draw the Lewis electron-dot symbol for nitrogen. Solution Step 1 Identify the chemical symbol for nitrogen. The symbol for nitrogen is N. Step 2 Determine the number of valence electrons in a nitrogen atom from its group number. Nitrogen belongs to group 5. Hence, it has five valence electrons. Step 3 Distribute the valence electrons around the chemical symbol one at a time. Pair the dots if all sides of the chemical symbols already have one electron. Let us Practice Draw the Lewis electron-dot symbol for phosphorus. Key Points A Lewis electron-dot symbol is used to represent the valence electrons of an element. Valence electrons are shown as dots around the element symbol. 21  The tendency of an element to gain, lose, or share electrons to attain eight electrons in its valence shell during chemical bonding is called the octet rule. An element that satisfies the octet rule is said to be chemically stable or inert. There are some exceptional cases where octet rule is not followed. Hydrogen and smaller elements form Lewis electron-dot structures with fewer than 8 electrons, while elements from period 3 and above can form structures with more than 8 electrons. Web Links For further readings, you can check the following web links: Want to know more about Gilbert N. Lewis? Visit this site to know his discoveries. Encyclopædia Britannica, Inc. 2018. ‘Gilbert N. Lewis.’ https://www.britannica.com/biography/Gilbert-N-Lewis Musically inclined? Want to sing the octet rule while learning it? “Because if you’re gonna understand, you’ve gottnna learn the rules!” Visit this site and sing with him. sciencemusicvideos. 2011. ‘Octet Rule song.’ https://www.youtube.com/watch?v=WzWk-mx_14E Check Your Understanding A. Draw the Lewis electron-dot symbol for the following elements. 1. potassium 6. tellurium 2. fluorine 7. barium 3. calcium 8. krypton 4. magnesium 9. cesium 5. oxygen 10. aluminum 22 B. Given the following hypothetical Lewis electron-dot symbols, choose which hypothetical element has the following properties described below. You can choose more than one answer. 1. has plausible Lewis electron-dot structure 2. has invalid Lewis electron-dot structure 3. found on the left side of the periodic table 4. found on the right side of the periodic table 5. belongs to the same family with nitrogen 6. the most stable element 7. the most reactive element 8. has a valence electron configuration of ns2 np3 9. did not follow Pauli’s exclusion principle 10. possibly a metalloid Briefly discuss the following. 1. Hydrogen and helium are two elements that do not follow the octet rule but are stable elements. What accounts for their stability? 2. Why do some elements in period 3 go beyond the octet rule and hold more than 8 electrons in their valence shells? 3. Main group metals such as magnesium have valence electrons less than four. What is the easiest way for them to satisfy octet rule? 4. Main group nonmetals such as sulfur have valence electrons more than four. What is the easiest way for them to satisfy octet rule? 5. How do the elements in group 4, which has exactly four valence electrons, satisfy octet rule? 23  Laboratory Activity Activity 6.1 Law of Definite Composition Objectives At the end of this laboratory activity, the students should be able to: calculate the mass percent of carbon in sodium bicarbonate; demonstrate the law of conservation of matter; and demonstrate the law of definite composition. Materials and Equipment baking soda (sodium bicarbonate), NaHCO3 vinegar (acetic acid), CH3COOH spatula graduated cylinder, 50 mL beaker, 250 mL watch glass top loading balance Procedure 1. Transfer 50 mL of vinegar into a 250 mL beaker using the graduated cylinder. 2. Weigh the beaker containing the vinegar in a top loading balance. Record the mass of the beaker and vinegar below. Record all observations under Trial 1 of the data table. 3. Weigh 1.5 g of baking soda on a watch glass. Use the tare function of the top loading balance to measure the mass of baking soda only. Record the mass of the baking soda on the data table. 4. Slowly add the baking soda to the vinegar in the beaker in such a way to prevent the solution from spilling. 5. Observe what happens in the solution. Record your observation below. 6. After all the baking soda has been added, let the beaker stand for three more minutes. Make sure that the reaction is complete. You may remove any bubbles remaining in the solution. 7. Record the mass of the beaker and the remaining content. Record them below. 24  8. Repeat Steps 1 to 7 twice for two more trials. Record them under Trials 2 and 3, respectively. Waste Disposal Dispose all remaining solutions in the sink with an excessive amount of running water. Data and Results Record your observations in the table below. Table 1. Data table for the determination of the mass percent of carbon in sodium bicarbonate. Parameter Trial 1 Trial 2 Trial 3 Average Mass of beaker and vinegar, (g) Mass of baking soda, (g) Mass of beaker after the reaction, (g) Mass of CO2 produced, (g) Mass of C produced, (g) Mass percent of C in NaHCO3 Guide Questions 1. What happens when you start adding baking soda to the beaker containing vinegar? 2. The reaction of vinegar with baking soda produces carbon dioxide as one of the products. This causes the bubbling or foaming of the content of the beaker while you are adding the baking soda. This observation is called effervescence. What is the amount of carbon dioxide produced by the reaction? Calculate for each trial and report it in the table above. 3. Calculate the ratio of the atomic weight of carbon to the molecular weight of carbon dioxide. The atomic weight of carbon is 12 g, while the molecular 25  weight of carbon dioxide is 44 g. Calculate for each trial and report it in the table above. 4. Multiply your answer from 2 to your answer from 3. This represents the mass of the carbon produced after the reaction. Calculate for each trial and report it in the table above. 5. Divide your answer from 4 to the mass of baking soda you have recorded. Calculate for each trial and report it in the table above. What does this tell you about the composition of baking soda? Performance Task Investigating Moisture Contents of Local Fertilizers Most compounds need water to function. Some have actual water molecules in their structures. Some incorporate moisture when they form. These water molecules are important to their function. One important moisture-containing material is fertilizer. The production and property of a fertilizer are highly affected by moisture content. Living in an agricultural country, this is important to us. Goal Your task is to design a method for determining the moisture content of fertilizers available in your local community. The goal is to determine whether the moisture present in your sample fertilizer follows production standards. The problem is how will you be able to devise a method which requires low cost but produce reliable results. The obstacle to overcome is the unavailability of chemical reagents and advanced technology in your community. Role You are the head of an agricultural committee in your community. Audience The target audience is the whole barangay community. You need to inform them that the fertilizers you have are good in terms of moisture content. 26 Situation You must carefully select at least five fertilizer samples. Conduct an experiment. Product, Performance, and Purpose: You will create a written report based on the results of the experiment. You will explain your methods on how you calculated the amount of moisture in each of your fertilizer samples. Standards and Criteria for Success: Your work must meet the standards found in the rubric below. Below Needs Successful Exemplary Criteria Expectations, Improvement Performance Performance 0% to 49% 50% to 74% 75% to 99% 100% Comprehensiveness Methods do not Shows some Comprehensive, Very justify the objectives comprehensive- some methods comprehensive, ness, but most meet the method methods are not objectives but carefully in line with the are not planned planned out, objectives well and techniques meet the objectives Reliability Methods produced Shows some Reliable, data Very reliable, no data reliability, data gathering and data gathering can be gathered analysis offers and analysis but cannot be reliable results offer highly analyzed further but sometimes reliable results show inconsistencies Innovativeness Does not exhibit Shows some Original ideas, Very original, effort to be original originality, adequate use of shows inadequate used resources imaginative use of resources of resources 27  Self Check After studying this unit, can you now do the following? Check I can… describe chemical bonding enumerate laws governing chemical bonding draw Lewis electron-dot symbols of elements explain octet rule explain why elements lose, gain or share electrons Key Words Chemical bond It is the force of attraction that holds the atoms together. Inert elements These are unreactive elements because of their completely-filled valence orbitals. They are also known as the noble gases. Law of conservation It states that mass is neither created nor destroyed but is of mass only transformed from one form to another. Law of definite It states that atoms of different elements combine in proportions fixed ratios of whole numbers to form compounds. It is also sometimes called the Law of definite composition. Law of multiple It states that elements may combine in several ratios of proportions whole numbers producing different compounds. Lewis electron-dot It is a representation of an element (or ion) that shows structure the valence electrons as dots arranged around the chemical symbol. 28 Octet Rule It states that molecules attain stability by achieving eight valence electrons. Wrap Up The Laws and Rules in Chemical Bonding References Chang, Raymond. 2010. Chemistry (10th Ed). New York: McGraw Hill. Ebbing, Darrell and Gammon, Steven D. 2011. General Chemistry Tenth Edition: Cengage Learning Moore, John W. and Stanitski, Conrad L. 2016. Chemistry The Molecular Science Fifth Edition: Cengage Learning Asia Pte Ltd 29 H. Eugene Lemay Jr, et al. 2002. Chemistry Connections to our Changing World: Prentice Hall Inc. Silberberg, Martin. 2009. Chemistry: The Molecular Nature of Matter and Change, 5th edition. Answer Key Lesson 6.2: Lewis Electron-Dot Symbol and the Octet Rule Let us Practice 1. 2. 3. 30