Chapter 22 Chemistry of the Nonmetals

1. Chemistry, The Central Science, 10th edition Theodore L. Brown, H. Eugene LeMay, Jr., and Bruce E. Bursten Chapter 22Chemistry of the Nonmetals John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice-Hall, Inc.

2. Nonmetals Except for hydrogen, the nonmetals are found in the upper right-hand corner of the periodic chart.

3. Periodic Trends Within a group, smaller atoms are more likely to form -bonds because they can get closer to other atoms.

4. Periodic Trends As a result, CO2 contains two -bonds, and SiO2 is a network solid with only -bonds.

5. Hydrogen • Discovered by Henry Cavendish (1731-1810) • Three isotopes • Protium (1H)  99.98% of all hydrogen • Deuterium (2H)  0.016% • Tritium (3H)  Radioactive

6. Properties of Hydrogen • Unique • Does not belong to any group • Very low melting (-259C) and boiling (-253C) points • Very large bond enthalpies • Reacts slowly • Reactions are generally quite exothermic

7. Hydrogen Production • Commercially produced from reaction of methane (CH4) with steam at 1100C or carbon and steam above 1000C CH4(g) + H2O (g) CO (g) + 3 H2(g) CO (g) + H2O (g)  CO2(g) + H2(g) C (s) + H2O (g)  H2(g) + CO (g) • Production from electrolysis of water not energy-efficient

8. Uses of Hydrogen • Most hydrogen used to produce ammonia (NH3) in the Haber process • Also used to produce methanol (CH3OH) CO (g) + 2 H2(g) CH3OH (g)

9. Uses of Hydrogen 2 H2(g) + O2(g) 2 H2O (g)H = -483.6 kJ • Using hydrogen as a fuel would have many advantages: • Highly exothermic reaction • Water is only product • Problem: How will we make the H2?

10. Hydrides • Three types • Ionic • Metallic • Molecular

11. Ionic Hydrides • Formed between hydrogen and alkali metals or heavy alkaline earth metals (Ca, Sr, Ba) • Very strong bases and reducing agents • React readily with water, so must be stored free from moisture

12. Metallic Hydrides • Formed between hydrogen and transition metals, often in unusual ratios • e.g., TiH1.8 • Retain electrical conductivity and other metallic properties

13. Molecular Hydrides • Formed between hydrogen and nonmetals or metalloids • Usually gases or liquids at room temperature and normal atmospheric pressure

14. Noble Gases • Extremely stable and unreactive • Liquid He (boiling point 4.2 K) used as a coolant • Ne used in electric signs • Ar used in light bulbs and as insulating gas between panes in thermal windows.

15. Xenon Compounds • Of all noble gases, Xe can be forced to form compounds most easily • KrF2 also known, but decomposes at -10C

16. Halogens • Have outer electron configurations of ns2np5 • Large electron affinities and ionization energies • Tend to accept one electron to form anion

17. Halogens • All have -1 oxidation state • All but fluorine also have positive oxidation states up to +7 when bonded to more electronegative atoms

18. Properties of Halogens • Tend to be good oxidizers, due to their electronegativity • Can oxidize anions of halides below them on periodic chart

19. Properties of Halogens • Fluorine has unusually high reduction potential • It can easily oxidize water: F2(aq) + H2O (l) 2 HF (aq) + 1/2 O2(g) E = 1.80 V

20. Uses of Halogens • Fluorine reacts to form fluorocarbon compounds used as lubricants, refrigerants and plastics. • Teflon is a polymer of fluorocarbons.

21. Uses of Halogens • Chlorine is the most-used halogen. • HCl • Plastics • Bleaches • Water purification

22. Uses of Halogens • Bromine is the anion for silver in photographic film. • KI is added to table salt as a dietary supplement.

23. Hydrogen Halides • Aqueous solutions of HCl, HBr, and HI are, of course, strong acids. • HF and HCl can be produced by reacting salts with H2SO4. • Br- and I- oxidize too easily, so one must use a weaker oxidizing acid, like H3PO4.

24. HF • Hydrofluoric acid reacts with silicates, components of most types of glass. • This reaction causes glass to etch. • Therefore, HF is usually stored in plastic containers.

25. Oxyacids and Oxyanions • Oxyacid strength increases with increasing oxidation number of central halogen • Oxyacids are strong oxidizers. • Oxyanions generally more stable than corresponding acids

26. Perchlorates While generally quite stable, perchlorates become exceedingly strong oxidizers when heated, and are used as rocket fuel.

27. Oxygen • Joseph Priestley discovered oxygen in 1774. • Lavoisier give it its name, which means “acid former.” • Most commercial oxygen is obtained from air.

28. Oxygen • Exists as one of two allotropes, O2 and O3 (ozone) • Forms very strong bonds • Reactions of oxygen-containing compounds have high activation energies • Reactions can be very exothermic, even to point of being explosive

29. Uses of Oxygen • Oxidizing agent • Bleach pulp and paper • Medical uses • Welding (with acetylene)

30. Ozone • Bluish gas with sharp odor • Extremely irritating to respiratory system • Stronger oxidizer than O2 • Used to purify water • Used in organic synthesis • Absorbs UV light in upper atmosphere

31. Oxides • Oxygen is second-most electronegative element • Always has negative oxidation state except when bonded to F • Acidic oxides like SO2 and SO3 form acids when exposed to water. • Basic oxides like BaO form hydroxide ion when they react with water.

32. Peroxides • Oxygen has oxidation state of -1 • O-O bond very weak • Decomposition of peroxides can be dangerously exothermic

33. Superoxides • Oxygen has oxidation state of -1/2 • The most active metals (K, Rb, Cs) form superoxides through reaction with O2 • React with H2O to form O2 • Source of O2 in self-contained breathing devices

34. Other Group 6A Elements • Have oxidation states of -2 as well as several positive oxidation states • Can have expanded octets

35. Selenium and Tellurium • Anions in minerals with Cu, Pb, Ag, and Au • Found as helical chains of atoms • Selenium not electrically conductive in dark, but quite so in light • Used in light meters, photosensors, and photocopiers

36. Sulfur • Solid, yellow compound found in 8-membered ring • As heated to melting, ring breaks and sulfur becomes viscous, reddish-brown liquid

37. Sulfur • Most sulfur used for H2SO4 and for vulcanization of rubber

38. Pyrites • Contain disulfide ion, S22-, the sulfur analog of peroxide • Found in minerals like iron pyrite (fool’s gold)

39. Sulfides • To say that many sulfides have rather unpleasant odors is a gross understatement. • H2S is emitted by rotten eggs. • Many minerals like galena (PbS) and cinnabar (HgS) are sulfides.

40. Sulfur Oxides, Oxyacids, and Oxyanions • SO2 is a poison, particularly to lower organisms. • Used to sterilize dried fruit and wine • Dissolves in H2O to form H2SO3 • Sulfites and bisulfites added to foods and wines to kill bacteria

41. Sulfur Oxides, Oxyacids, and Oxyanions • Sulfuric acid • Strong acid • Good dehydrating agent • Decent oxidizer

42. Sulfur Oxides, Oxyacids, and Oxyanions • Thiosulfate ion resembles sulfate ion (a S replaces one of the O’s in sulfate) • Sodium thiosulfate pentahydrate (Na2S2O35 H2O) used in photography to remove unexposed AgBr from film as soluble complex of thiosulfate Sulfate Thiosulfate

43. Nitrogen • Discovered in 1772 by Daniel Rutherford • Makes up 78% of Earth’s atmosphere • Can exist in oxidation states from -3 to +5

44. Nitrogen • Many nitrogen-containing compounds strong oxidizers • N2 made into NH3 in Haber process • NH3 is precursor to many other compounds

45. Ammonia • Hydrazines made from ammonia • One intermediate is chloramine (NH2Cl), poisonous compound produced when household ammonia and hypochlorite ion in bleach are mixed • Hydrazines are strong oxidizers used in rocket fuels

46. Oxides and Oxyacids • Nitrous oxide (N2O; laughing gas) was the first general anesthetic. • It is also used in aerosol products like whipped cream.

47. Oxides and Oxyacids • Nitric oxide (NO) is a slightly toxic, colorless gas. • Recently shown to be neurotransmitter in humans involved in vasodilation • Reacts with O2 in air to produce nitrogen dioxide, NO2

48. Oxides and Oxyacids • Nitric acid • Strong acid and oxidizer • Used in fertilizer and explosive production (TNT, nitrocellulose, nitroglycerine) • Nitrous acid • Less stable, yet weaker acid than HNO3

49. Other Group 5A Elements This group contains nonmetals (N and P), a metal (Bi), and metalloids (As and Sb).

50. Phosphorus • Two allotropes • White phosphorus (P4) • Highly strained • Bursts into flames if exposed to O2 in air • Red phosphorus • Very stable