Compounds & Chemical Formulas

1. Compounds & Chemical Formulas

2. Common Compounds • H2O • water • the most common compound on the earth’s surface • SiO4 • silicate • the most common compound in the earth’s crust

3. There are millions of compounds! Common Compounds • C6H12O6 • glucose • C55H72O5N4Mg • chlorophyll

4. H O H C H O O C H H O C C H O C H O H

5. matter puresubstances mixtures

6. matter puresubstances compounds mixtures elements iron gold lead uranium sodium chloride glucose calcium carbonate water

7. matter puresubstances mixtures elements compounds iron gold lead uranium sodium chloride glucose calcium carbonate water

8. homogeneousmixtures heterogeneousmixtures mixtures air gasoline 14 karat gold seawater granite soil blood chocolate cake

9. matter puresubstances mixtures elements compounds homogeneousmixtures heterogeneousmixtures iron gold lead uranium sodium chloride glucose calcium carbonate water air gasoline 14 karat gold seawater granite soil blood chocolate cake

10. PureSubstances contain only one kind of matter

11. Elements All atoms are the same.

12. Compounds • made up entirely of the same molecules or ions • have the same ratio of elements

13. Compounds 2 types Organic Inorganic • do not have carbon • water, table salt • contain carbon • living things

14. Mixtures • combinations of substances • physically placed together, not bonded • no set ratio

15. Mixtures 2 types Homogeneous Heterogeneous

16. Homogeneous • Particles about the same size • Separate types of particles not usually visible • Called solutions Examples: saltwater, alloys

17. Heterogeneous • nonuniform—different sized particles • Separate types of particles can often be seen. Examples: soil, vegetable stew, wood, concrete

18. Chemical Formulas • A shorthand way to show the composition of a pure substance • Show how many atoms of each element make up a substance

19. Chemical Formulas • Example: Rust • Its chemical formula is Fe2O3, iron oxide. • The 2 and 3 are subscripts which tell how many atoms of each element are present in one molecule of rust.

20. What part of a chemical formula tells the number of atoms of each element? • Subscript • Molecule • Empirical formula • Definite composition

21. Chemical Formulas • Empirical Formula • Gives only the ratio of atoms • Not necessarily unique to a substance • May be the same as the actual chemical formula

22. We can predict the formula based on the number of valence electrons. Chemical Formulas • How do we know that the formula for table salt is NaCl? • Why can’t it be NaCl2 (as in MgCl2,magnesium chloride)?

23. Oxidation Number The number of electrons that a bonded atom would have to gain or lose to return to its neutral state.

24. Oxidation Number • If a metal has lost electrons, it will have to regain them to return to its neutral state. • Therefore, it has a positive oxidation number. • A nonmetal tends to gain electrons, so it will have a negative oxidation number.

25. + 1 + 2 Li Be + 3 + 4 B C – 4

26. – 3 – 2 N O – 1 0 F Ne

27. Oxidation Number • How do we know the oxidation number of an atom? • By knowing which group it is in.

28. Oxidation Number • Group 1A (alkali) metals have one outer electron, which they tend to lose. • What would be the charge of the ion if it loses one electron? + 1

29. Oxidation NumberExample • Sodium 11 electrons (–) 11 protons (+) • If it loses one electron: • Sodium 10 electrons (–) 11 protons (+) = 0 = +1

30. What is the charge on a Group 1A element when it loses an electron? • – 1 • + 1 • 0 • + 2

31. Oxidation Number • Group 2A metals (alkaline-earth) lose two electrons. • What oxidation number do they have? + 2

32. Oxidation Number • What is the oxidation number of • Group 3A elements? • Group 8A elements? • Group 7A elements? • Group 6A elements? + 3 0 – 1 – 2

33. Oxidation Number • What is the oxidation number of • Group 5A elements? • Group 4A elements? + 5, – 3 + 4, – 4

34. To write a chemical formula, we must know the • atoms. • molecules. • oxidation numbers. • substance.

35. What tells us the oxidation number of an atom? • Its size • Its group • Its color • Its subscripts

36. What is the oxidation number of lithium? +1

37. What is the oxidation number of beryllium? +2

38. 0 0 0 0 Na Ar O2 S8 Oxidation Number Rules Rule 1: Free Element Rule The oxidation number (ON) of pure elements is 0.

39. 2+ 3+ 4+ + – K Fe Al Sn Cl Oxidation Number Rules Rule 2: Ion Rule The ON of a monatomic ion equals its charge. +1 +2 +3 +4 –1

40. Oxidation Number Rules • Rule 3: Specific ON Rule • Certain families have the same ON. • Alkali metals = +1 • Alkaline earth metals = +2

41. Oxidation Number Rules • Rule 3: Specific ON Rule • Certain families have the same ON. • Hydrogen = +1 (when bonded to another nonmetal) • Hydrogen = –1 (when bonded to metals)

42. Oxidation Number Rules • Rule 3: Specific ON Rule • Certain families have the same ON. • Oxygen = –2 (except when bonded to fluorine) • Halogens = –1 (when bonded to metals)

43. Oxidation Number Rules Rule 4: Zero Sum Rule The sum of the oxidation numbers of all atoms in a compound must equal zero. +1 –1 0 + – Na + Cl NaCl

44. Oxidation Number Rules Rule 4: Zero Sum Rule The sum of the oxidation numbers of all atoms in a compound must equal zero. 0 0 (+1) (+1) 2 –2 -3 3 H2O NH3

45. Oxidation Number Rules Rule 4: Zero Sum Rule The sum of the oxidation numbers of all atoms in a compound must equal zero. 0 0 (–1) +3 3 (–1) +2 2 AlCl3 CaI2

46. What is the oxidation number of F in AlF3? –1

47. What is the oxidation number of Fe in FeCl2? 2

48. Writing Chemical Formulas If we know the elements and their oxidation numbers, we can predict the formula of a compound.

49. Writing Chemical Formulas • Write the less electronegative element first. • Find the oxidation number of the elements. +3 –1 Al F

50. Writing Chemical Formulas • Change the number of atoms of the elements so that the sum of the oxidation numbers equals 0. 0 +3 –1 (–1) 3 F3 Al F