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COMPOUNDS

COMPOUNDS. Chapter Sixteen: Compounds. 16.1 Chemical Bonds and Electrons 16.2 Chemical Formulas 16.3 Molecules and Carbon Compounds. Chapter 16.1 Learning Goals. Infer the relationship between the number of valence electrons and the behavior of atoms.

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COMPOUNDS

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  1. COMPOUNDS

  2. Chapter Sixteen: Compounds • 16.1 Chemical Bonds and Electrons • 16.2 Chemical Formulas • 16.3 Molecules and Carbon Compounds

  3. Chapter 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.

  4. Key Question: Why do atoms form chemical bonds? Investigation 16A Chemical Bonds

  5. 16.1 Chemical Bonds and Electrons • A chemical bond forms when atoms transfer or share electrons. • A covalent bond is formed when atoms share electrons.

  6. 16.1 Chemical formulas • A molecule’s chemical formula tells you the ratio of atoms of each element in the compound.

  7. 16.1 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.

  8. 16.1 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.

  9. 16.1 Reactivity • In chemistry, reactivemeans 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.

  10. 16.1 Valence electrons • Chemical bonds are formed only between the electrons in the highest unfilled energy level. • These electrons are called valence electrons.

  11. 16.1 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?

  12. 16.1 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.

  13. 16.1 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.

  14. 16.1 Lewis dot diagrams • A 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?

  15. Chapter Sixteen: Compounds • 16.1 Chemical Bonds and Electrons • 16.2 Chemical Formulas • 16.3 Molecules and Carbon Compounds

  16. Chapter 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.

  17. Key Question: Why do atoms combine in certain ratios? Investigation 16B Chemical Formulas

  18. 16.2 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.

  19. 16.2 Oxidation Numbers • A 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?

  20. 16.2 Ionic bonds • On the periodic table, strong electrondonorsare 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.

  21. 16.2 Covalent bonds • Covalent 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.

  22. 16.2 Oxidation numbers and chemical formulas • Remember, the oxidation numbers for all the atoms in a compound must add up to zero.

  23. 16.2 Oxidation numbers • Some periodic tables list multiple oxidation numbers for most elements. • This is because more complex bonding is possible.

  24. Solving Problems • Iron 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.

  25. Solving Problems • Looking for: • …formula for a binary compound • Given • … Fe3+ and O2– • Relationships: • Write the subscripts so that the sum of the oxidation numbers equals zero. • Solution • Two iron atoms = 2 × (3+) = 6+ • Three oxygen atoms = 3 × (2–) = 6–

  26. Solving Problems 2- 3+ Fe O 3 x 2 = 6

  27. 2- 2- 2- 3+ 3+ Fe Fe O O O = -6 = +6 0 Solving Problems + + + +6 -6

  28. Solving Problems 2- 3+ Fe O 2 3

  29. 16.2 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.”

  30. 16.2 Some polyatomic ions

  31. Solving Problems • Al3+ combines with sulfate (SO4)2– to make aluminum sulfate. • Write the chemical formula for aluminum sulfate.

  32. Solving Problems • Looking for: • …formula for a ternary compound • Given • … Al3+ and SO42– • Relationships: • Write the subscripts so that the sum of the oxidation numbers equals zero. • Solution • Two aluminum ions = 2 × (3+) = 6+ • Three sulfate ions = 3 × (2–) = 6–

  33. Solving Problems 3+ 2- Al (SO4) 2 3

  34. Chapter Sixteen: Compounds • 16.1 Chemical Bonds and Electrons • 16.2 Chemical Formulas • 16.3 Molecules and Carbon Compounds

  35. Chapter 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.

  36. Key Question: What are some common molecules that contain carbon? Investigation 16C Carbon and its Chemistry

  37. 16.3 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 diagramsto show the shape and arrangement of atoms in a molecule.

  38. 16.3 Structural diagrams • Two substances have the same formula as aspirin, but not its pain relieving properties.

  39. 16.3 The chemistry of carbon • Carbon molecules come in three basic forms: straight chains, branching chains, and rings. • All three forms are found in important biological molecules.

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