2Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons16.2 Chemical Formulas16.3 Molecules and Carbon Compounds
3Chapter 16.1 Learning Goals Infer the relationship between the number of valence electrons and the behavior of atoms.Compare and contrast ionic and covalent bonding.Draw Lewis diagrams to represent the valence electrons of atoms.
4Chemical Bonds Investigation 16A Key Question: Why do atoms form chemical bonds?
516.1 Chemical Bonds and Electrons A chemical bond forms when atoms transfer or share electrons.A covalent bond is formed when atoms share electrons.
616.1 Chemical formulasA molecule’s chemical formula tells you the ratio of atoms of each element in the compound.
716.1 Ionic bonds Not all compounds are made of molecules. Ionic bonds are bonds in which electrons are transferred from one atom to another.Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.
916.1 Why chemical bonds form It takes energy to separate atoms that are bonded together.The same energy is released when chemical bonds form.Atoms form bonds to reach a lower energy state.
1016.1 ReactivityIn chemistry, reactive means an element readily forms chemical bonds, often releasing energy.Some elements are more reactive than others.The closer an element is to having the same number of electrons as a noble gas, the more reactive the element is.
1416.1 Valence electrons and the periodic table Going from left to right across a period each new element has one more valence electron than the one before it.How many valence electrons does nitrogen have?
1516.1 Valence electrons and the periodic table Oxygen combines with one beryllium atom because beryllium can supply two valence electrons to give oxygen its preferred number of 8.
1616.1 Valence electrons and the periodic table Carbon has four valence electrons.Two oxygen atoms can bond with a single carbon atom, each oxygen sharing two of carbon’s four valence electrons.The bonds in carbon dioxide (CO2) are double bonds because each bond involves 2 electrons.
1716.1 Lewis dot diagramsA clever way to keep track of valence electrons is to draw Lewis dot diagrams.A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons.What is the dot structure for nitrogen?
21Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons16.2 Chemical Formulas16.3 Molecules and Carbon Compounds
22Chapter 16.2 Learning Goals Use the periodic table to make predictions about whether atoms will most likely form ionic or covalent bonds.Describe how oxidations numbers can be used to write chemical formulas of compounds.Correctly name chemical compounds.
23Chemical Formulas Investigation 16B Key Question: Why do atoms combine in certain ratios?
2416.2 Chemical Formulas and Oxidation Numbers All compounds have an electrical charge of zero (they are neutral).An oxidation number indicates the charge on the atom (or ion) when electrons are lost, gained, or shared in chemical bonds.
2516.2 Oxidation NumbersA sodium atom always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound.Therefore, we say that sodium has an oxidation number of 1+.What is chlorine’s oxidation number?
2716.2 Ionic bondsOn the periodic table, strong electron donors are the left side (alkali metals).Strong electron acceptors are on the right side (halogens).The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.
28As heat energy is added to ice, the temperature increases until it reaches 0°C. Then the temperature stops increasing.As you add more heat, more ice becomes liquid water but the temperature stays the same.This is because the added energy is being used to break the intermolecular forces and change solid into liquid.Once all the ice has become liquid, the temperature starts to rise again if more energy is added.
2916.2 Covalent bondsCovalent compounds form when elements have roughly equal tendency to accept electrons.Elements that are both nonmetals and therefore close together on the periodic table tend to form covalent compounds.
3016.2 Oxidation numbers and chemical formulas Remember, the oxidation numbers for all the atoms in a compound must add up to zero.
31As heat energy is added to ice, the temperature increases until it reaches 0°C. Then the temperature stops increasing.As you add more heat, more ice becomes liquid water but the temperature stays the same.This is because the added energy is being used to break the intermolecular forces and change solid into liquid.Once all the ice has become liquid, the temperature starts to rise again if more energy is added.
3216.2 Oxidation numbersSome periodic tables list multiple oxidation numbers for most elements.This is because more complex bonding is possible.
34Predict the chemical formula of this compound. Solving ProblemsIron and oxygen combine to form a compound. Iron (Fe) has an oxidation number of 3+. Oxygen (O) has an oxidation number of 2–.Predict the chemical formula of this compound.
35Solving Problems Looking for: Given Relationships: Solution …formula for a binary compoundGiven… Fe3+ and O2–Relationships:Write the subscripts so that the sum of the oxidation numbers equals zero.SolutionTwo iron atoms = 2 × (3+) = 6+Three oxygen atoms = 3 × (2–) = 6–
3916.2 Polyatomic ions Compounds can contain more than two elements. Some of these types of compounds contain polyatomic ions.A polyatomic ion has more than one type of atom.The prefix poly means “many.”
41Al3+ combines with sulfate (SO4)2– to make aluminum sulfate. Solving ProblemsAl3+ combines with sulfate (SO4)2– to make aluminum sulfate.Write the chemical formula for aluminum sulfate.
42Solving Problems Looking for: Given Relationships: Solution …formula for a ternary compoundGiven… Al3+ and SO42–Relationships:Write the subscripts so that the sum of the oxidation numbers equals zero.SolutionTwo aluminum ions = 2 × (3+) = 6+Three sulfate ions = 3 × (2–) = 6–
44Chapter Sixteen: Compounds 16.1 Chemical Bonds and Electrons16.2 Chemical Formulas16.3 Molecules and Carbon Compounds
45Chapter 16.3 Learning Goals Explain the significance of carbon in the structure of many different molecules.Describe the importance of carbon to living organisms.Compare and contrast the structure and function of carbohydrates, lipids, proteins, and nucleic acids.
46Carbon and its Chemistry Investigation 16CCarbon and its ChemistryKey Question:What are some common molecules that contain carbon?
4716.3 Molecules and Carbon Compounds In addition to the elements from which it is made, the shape of a molecule is also important to its function and properties.We use structural diagrams to show the shape and arrangement of atoms in a molecule.
4816.3 Structural diagramsTwo substances have the same formula as aspirin, but not its pain relieving properties.
5216.3 Organic compoundsOrganic chemistry is the branch of chemistry that specializes in carbon compounds, also known as organic molecules.Plastic, rubber, and gasoline are important carbon compounds.Scientists classify the organic molecules in living things into four basic groups: carbohydrates, proteins, fats, and nucleic acids.
5316.3 CarbohydratesCarbohydrates are energy-rich compounds made from carbon, hydrogen, and oxygen.Carbohydrates are classified as either sugars or starches.
5416.3 CarbohydratesCarbohydrates are mainly composed of carbon, hydrogen, and oxygen in a ratio of about 1:2:1.Glucose, C6H12O6, is a simple sugar.Table sugar is a carbohydrate called sucrose.
5516.3 CarbohydratesStarches are long chains of simple sugars joined together.Cellulose is the primary molecule in plant fibers, including wood.
5616.3 LipidsLike carbohydrates, lipids are energy- rich compounds made from carbon, hydrogen, and oxygen whose ratio is much less than 1:2:1.Lipids include fats, oils, and waxes.
5716.3 Lipids A typical fat molecule has a two- part structure: glycerol fatty acid chains
5816.3 Saturated or unsaturated fat? In a saturated fat, carbon atoms are surrounded by as many hydrogen atoms as possible.An unsaturated fat has fewer hydrogen atoms than it could have.
5916.3 ProteinsProteins are basic molecular building blocks of cells and all parts of animals.Proteins are among the largest organic molecules.Why is the shape of aprotein important?
6016.3 Enzymes Enzymes are proteins. An enzyme is a type of protein that cells use to speed up chemical reactions in living things.
6116.3 ProteinsProtein molecules are made of smaller molecules called amino acids.Your cells combine different amino acids in various ways to make new and different proteins.
6216.3 Nucleic AcidsNucleic acids are compounds made of long, repeating chains called nucleotides.Each nucleotide contains:a sugar moleculea phosphate molecule, anda base molecule.
6316.3 DNA and nucleic acids DNA is a nucleic acid . A DNA molecule is put together like a twisted ladder.This model shows a short piece of the flattened DNA ladder.A DNA molecule is usually twisted and much longer.
6416.3 DNA Each side of the ladder is made of: 5-carbon sugars called deoxyriboseand phosphate groups.
6516.3 DNAThere are four nitrogen bases in two matched pairs.
67The Spin on Scrap TiresAs the number of cars on the road increases each year, so does the number of scrap tires. For many years, the only disposal options were to throw scrap tires into landfills or burn them, which caused air pollution. Today, scientists and engineers are coming up with innovative ways to put a new spin on discarding old tires.