The Representative Elements

1. The Representative Elements • Representative elements • chemical properties are determined by the valence s and p electrons • include elements in group IA through VIIIA • Diagonal line divides the metals from the nonmetals • 8 metalloids exhibit both metallic and nonmetallic properties

2. The Representative Elements • Metals vs. Nonmetals • Metals tend to lose valence electrons to form cations • Nonmetals tend to gain valence electrons to form anions • Metallic character increases going down a group (I.E. Decreases going down a group)

3. The Representative Elements • Size and Group Anomalies • Different properties between elements in the first row of a group than the elements in the second row due to the large differences in the atomic radii • H is very different from Li due to H’s very small size • H has a greater attraction for electrons than Li, so H can form covalent bonds, Li and the other Group I elements lose electrons

4. The Representative Elements • Oxides of Group IIA are basic except • BeO is amphoteric • because Be is so small, BeO has some covalent character • Dramatic difference between C chemistry and silicon chemistry • Organic chemistry - deals with stable compounds with many C - C bonds • Silicon chemistry - mostly Si - O bonds. • Compounds with Si-Si bonds are more reactive

5. The Representative Elements • Carbon • can form p bonds, C=C, C=O, etc. • Silicon • difficult to form p bonds • Si’s 3p orbital cannot overlap with O’s 2p orbital ...due to differences in size

6. The Representative Elements • Nitrogen • forms p bonds, e.g. N = N, very very stable • Phosphorus • like Si, does not form p bonds, though it does form aggregates of atoms, like P4 • Oxygen • forms bonds, e.g. O=O, very stable • Sulfur • Sulfur atoms form aggregates, such as the cyclic S8

7. The Representative Elements • Still on the subject of size... • F has a smaller electron affinity than Cl, which is the reverse of the expected trend • Why? F is so small that the electron pairs tend to repel each other. • The F2 bond is weaker than the Cl2 bond, again because F’s small size allow the lone pairs to get closer together, repelling each other, and so weakening the bond

8. The Representative Elements • Abundance and Preparation • In the earth’s crust, oceans and atmosphere: • Oxygen 49.2% • Silicon 25.7% • Aluminum 7.50% • Iron 4.71% • Calcium 3.39%

9. The Representative Elements • Abundance and Preparation • In the human body: • Oxygen 65.0% • Carbon 18.0% • Hydrogen 10.0% • Nitrogen 3.0% • Calcium 1.4%

10. The Representative Elements • Abundance and Preparation • Only 1/4 of the elements occur naturally in the free state • Metallurgy - process of obtaining a metal from its ore • usually involves the reduction of the metal • Carbon is the usual choice for a reducing agent • Electrolysis is used to reduce the most active metals

11. The Representative Elements • Preparation of Nonmetals • Liquefaction/distillation of air to obtain N2 and O2 • based on their different boiling points • N2 - second in amount manufactured in the U.S. • O2 - fourth in amount manufactured in the U.S. • H2 - obtained from the electrolysis of water and the decomposition of methane • Sulfur - found underground in elemental form, recovered using the Frasch process

12. The Representative Elements • Group IA Elements • ns1 outer electron configuration • very active metals (except for hydrogen) • the alkali metals • react vigorously with water to produce hydrogen gas: • 2M + 2 H2O(l) --> 2 M+ + 2 OH- + H2 • Li is the only alkali metal to form the oxide in presence of excess oxygen: • 2Li(s) + O2(g) --> 2Li2O(s)

13. The Representative Elements • 2 Na(s) + O2(g) --> Na2O(s) (in limited oxygen) • In excess oxygen, sodium forms the peroxide: • 2Na + O2 --> Na2O2 • the sodium peroxide reacts with water to form hydrogen peroxide • Na2O2 + 2H2O --> H2O2 +2 Na+ + 2OH- • Potassium, rubidium and cesium react with oxygen to produce superoxides, MO2 • Ex: K(s) + O2(g) --> KO2(s) • The superoxides release oxygen gas in water or carbon dioxide

14. The Representative Elements • 2KO2 + 2H2O --> 2K+ + 2OH- + O2 + H2O2 • 4KO2 + 2CO2 --> 2K2CO3(s) + 3O2 • these superoxides are used in the breathing apparatus used by firefighters • Lithium is the only alkali metal to react with nitrogen gas: • 6Li + N2 --> 2Li3N(s)

15. The Representative Elements Element Source Method of Preparation Lithium silicate minerals electrolysis of molten LiCl Sodium NaCl electrolysis of molten NaCl Potassium KCl electrolysis of molten KCl

16. The Representative Elements • Hydrogen • colorless, odorless gas composed of H2 molecules • low MM, nonpolar, very low B.P. (-253oC), very low M.P. (-253oC) • highly flammable, explosive • Industrial source: reaction of methane and water: • CH4 + H2O --> CO + 3H2 • Also a byproduct of cracking large hydrocarbons in gasoline production

17. The Representative Elements • Hydrogen • pure hydrogen can be produced by the electrolysis of water, but not economically feasible • Industrial uses • production of ammonia (Haber process) • hydrogenation of unsaturated vegetable oils • Chemical Behavior • typical nonmetal • forms covalent compounds with other nonmetals • forms salts with active metals

18. The Representative Elements • Hydrides • Ionic (saltlike) hydrides • when hydrogen combines with very active metals from Group I or Group II • the hydride ion (H-) is a strong reducing agent • ionic hydrides react violently in water: • LiH + H2O --> H2 + Li+ + OH- • Covalent hydrides • when hydrogen combines with other nonmetals, e.g. in HCl, NH3, CH4, and H2O

19. The Representative Elements • Metallic hydrides • formed when transition metal crystals are treated with hydrogen gas • the hydrogen atoms migrate into the crystal structure to occupy holes or interstices • a solid solution is formed • when these interstitial hydrides are heated, H2 gas is released • use these intersitial hydrides for hydrogen gas storage

20. The Representative Elements • Group IIA Elements • ns2 outer electron configuration • very reactive • alkaline earth metal elements • the oxides of the Group II elements form bases in water: MO(s) + H2O --> M+2 + 2 OH- • BeO can act as an acid as well: • BeO(s) + 2 OH- + H2O --> Be(OH)4-2 • Group II metals react with water to form H2: • M(s) + 2H2O(l) --> M+2 + 2 OH- + H2(g)

21. The Representative Elements • Source of Group II elements: • electrolysis of molten chlorides of the Group II elements • Heavier Group II elementsreact with nitrogen or hydrogen to form the nitride or hydride salts: • 3 Ca(s) + N2 --> Ca3N2(s) • Ca(s) + H2 --> CaH2(s)

22. The Representative Elements • Practical importance of alkaline earth metals • Calcium • found in structural minerals in bones and teeth • Magnesium • as Mg+2 plays a vital role in metabolism and muscle function • used to produce the bright light for photographic flash units: 2 Mg + O2 --> 2MgO + light • useful structural material, especially when alloyed with aluminum (low density and moderate strength) • both Ca+2 and Mg+2 make water “hard” • hard water interferes with detergent action and prevents soaps from lathering

23. The Representative Elements • Group IIIA Elements • ns2np1 • metallic character increases going down the group • Boron • BH3 is actually unstable, while diborane, B2H6, is stable • boranes are electron deficient, so are very reactive • Aluminum • most abundant metal on earth • has metallic physical properties (high thermal and electrical conductivities, lustrous appearance) • bonds covalently to nonmetals • Al2O3 is amphoteric

24. The Representative Elements • Gallium • unusually low melting point (30oC) • largest liquid range between the mp and bp (b.p. = 2400oC) • makes gallium useful for thermometers, especially for high temperatures • expands like water when it freezes • is amphoteric like aluminum

25. The Representative Elements • Indium • chemistry is similar to aluminum and gallium • can form +1 ion as well as +3 ions • Thallium • completely metallic • Tl2O3 is a basic oxide • has a +1 and +3 oxidation state

26. The Representative Elements • Group IVA Elements • ns2np2 • contains two of the most important elements on earth: Carbon and Silicon • all Group IVA elements can form four covalent bonds to nonmetals: CH4, SiH4, GeBr4, SnCl4, and PbCl4 • form tetrahedral molecules with sp3 hybridization

27. The Representative Elements • Carbon • can form p bonds • C-C bond is stronger than the Si-Si bond, so carbon chemistry is dominated by the C-C bond, while silicon chemistry is dominated by the Si-O bond • 2 allotropic forms found in the earth’s crust • diamond and graphite • buckminsterfullerene, C60, and other related substances have been characterized

28. The Representative Elements • Three oxides of carbon • CO, carbon monoxide, by-product of incomplete combustion of carbon compounds • CO2, carbon dioxide, product of human and animal respiration and combustion of fossil fuels, produced in fermentation • dissolves in water to form an acidic solution: • CO2 + H2O --> H+ + HCO3- • O=C=C=C=O, carbon suboxide!!

29. The Representative Elements • Silicon • second most abundant element on earth • metalloid • distributed in silica and silicates • 85% of the earth’s crust is composed of these silica and silicates • major use is in semiconductors

30. The Representative Elements • Germanium • relatively rare element, metalloid, used in semiconductors • Tin • soft, silvery white metal • used in alloys such as bronze (Sn & Cu), solder (Sn & Pb), and pewter (Sn, Cu, Bi, and Sb) • three allotropes • white tin, gray tin, and brittle tin (all stable at different temperatures)

31. The Representative Elements • Tin • current use - protective coating (applied electrolytically) for steel, especially in food containers • +2 and +4 oxidation states • Tin(IV) halides contain covalent Sn-X bonds, not ionic bonds, behave more like molecular compounds than ionic compounds • Tin(IV) halides are very volatile • Tin (II) halides are probably ionic, and are less volatile • SnF2 was used in toothpaste

32. The Representative Elements • Lead • obtained from the ore, galena, PbS • melts at a low temperature • may have been the first metal every obtained from its ore (lead was used as early as 3000 B.C.) • lead is toxic…Roman civilization may have crumbled partly due to lead poisoning as analysis of bones from that era show high lead concentrations • largest commercial use of lead is for electrodes in the lead storage battery

33. The Representative Elements • Lead • forms +2 and +4 oxidation states • lead (II) halides exhibit ionic properties • only PbCl4 and PbBr4 exist (only possible lead (IV) halides) • PbO (lead (II) oxide) - used to glaze ceramics • PbO2 (lead (IV) oxide) does not exist in nature

34. The Representative Elements • Group VA elements • ns2np3 • varied chemical properties among the members of the group • metallic character increases going down the group • N and P are nonmetals • Bi and Sb are metallic • too much energy is required to remove 5 electrons, so no ionic compound containing Bi+5 or Sb+5 exist • SbCl5 and BiF5 are actually molecular

35. The Representative Elements • Bi and Sb are strong oxidizing agents in the+5 oxidation state • BiF5 is a good fluorinating agent: • BiF5 --> BiF3 + F2 • Bi+3 and Sb+3 salts are quite common • All of the Group VA elements, except for N, can form molecules with 5 covalent bonds • N cannot form molecules with covalent bonds because of its small size and lack of d orbitals

36. The Representative Elements • Elements in Group VA, except for N, do not readily form pi bonds • N2 consists of a triple bond between the nitrogen atoms • P4, As4, and Sb4 are all singly bonded

37. The Representative Elements • The Chemistry of Nitrogen • all elemental nitrogen on earth exists as N2 with a very strong triple bond (941 kJ/mole) • N2 is very unreactive; it can coexist with most other elements without any significant reaction • N2 makes a good inert atmosphere to run reactions with substances that normally react with oxygen or water • Because of N2’s triple bond, most binary compounds containing nitrogen decompose exothermically to form N2 • e.g. N2O --> N2 + 1/2 O2DHo = -82 kJ

38. The Representative Elements • Thermodynamic stability of N2 • nitrogen based explosives: • 4C3H5N3O9(l) --> 6 N2(g) + 12 CO2(g) + 10H2O(g) + O2(g) + energy nitroglycerin • 4 moles of liquid nitroglycerin yields 29 moles of gaseous products, producing a large increase in volume as well as very stable molecules with strong bonds, hence an explosion occurs with hot, rapidly expanding gases • Dynamite - invented by Alfred Nobel in 1867 • absorb this highly unstable nitroglycerin onto porous silica to make its handling safer

39. The Representative Elements • More Nitrogen based explosives • most high explosives are organic compounds that contain nitro (-NO2) groups to produce nitrogen and other gases as products • TNT - trinitotoluene: • 2C7H5N3O6(s) --> 12CO(g) + 5H2(g) + 2C(s) + energy

40. The Representative Elements • Nitrogen fixation • transforming N2 to other nitrogen containing compounds • Haber process, the synthesis of ammonia, is an example of nitrogen fixation • the ammonia can be applied to the soil as a fertilizer • high temperature combustion process in automobile engines • nitrogen reacts with oxygen to form NO • NO reacts with oxygen to form NO2 (contributor to photochemical smog) • NO2 reacts with moisture to form nitrate salts, which are plant nutrients

41. The Representative Elements • Natural nitrogen fixation • N2 + O2 react together to form nitrogen oxides with the help of lightning to disrupt the strong bonds • studies indicate that lightning may account for half of the fixed nitrogen available on earth • Nitrogen fixing bacteria in the root nodules of legumes such as beans,peas, and alfalfa, allow for the conversion of N2 to ammonia and other nitrogen containing compounds useful to plants • much more efficient than the Haber process (bacteria work at soil temperature and 1 atm pressure, the Haber process runs at 400oC and 250 atm!

42. The Representative Elements • The Nitrogen Cycle • 10 million more tons more nitrogen is currently being fixed by natural and human processes than is being returned to the atmosphere • the fixed nitrogen accumulates in the soil, lakes, rivers, and oceans where it promotes algae growth as well as growth of other undesirable organisms • Denitrification - bacteria can return the nitrogen in nitrogen containing compounds to the atmosphere as nitrogen gas

43. The Representative Elements • Nitrogen Hydrides • Ammonia - most important of the nitrogen hydrides • toxic, colorless gas, manufactured in large quantities (30 billion pounds per year, used mainly in fertilizers • unusually high B.P. (-33.4oC), for a substance with such a low MM, due to Hydrogen bonding • Hydrazine, N2H4 • colorless liquid with an ammonia-like odor • powerful reducing agent • used as a rocket propellant • used as a blowing agent (because it produces N2(g) upon decomposition) in the manufacture of plastics • used in agricultural pesticides

44. The Representative Elements • Nitrogen Oxides • Nitrogen forms a series of oxides in which nitrogen has oxidation states from +1 to +5 • N2O - dinitrogen monoxide, aka, nitrous oxide, aka, laughing gas • also a mild anesthetic, a propellant in aerosol cans of whipped cream • exists in the atmosphere as a result of soil microorganisms, helps to control the earth’s temperature because it can absorb infrared radiation

45. The Representative Elements • Nitrogen Monoxide • NO, commonly called nitric oxide • colorless gas produced when nitric acid reacts with copper metal • in oxygen, the NO is oxidized to form the brown gas, NO2 • may behave as a neurotransmitter in the body • has an odd number of electrons, is paramagnetic (use MO diagrams), and is thermodynamically unstable: • 3NO(g) --> N2O(g) + NO2(g)

46. The Representative Elements • Nitrogen Dioxide • NO2, also contains an odd number of electrons, is paramagnetic, and dimerizes to form N2O4: • 2NO2 --> N2O4 • Dinitrogen Trioxide • N2O3 - least common, a blue liquid that dissociates into NO and NO2, and N2O5

47. The Representative Elements • Oxyacids of Nitrogen • Nitric acid - HNO3 • 10 million tons produced per year • used in the manufacture of many products such as nitrogen based explosives and ammonium nitrate • produced commercially by the oxidation of ammonia in the Ostwald process • 4NH3 + 5O2 --> 4NO + 6 H2O • 2NO + O2 --> 2NO2 • 3NO2 + H2O --> 2HNO3 + NO

48. The Representative Elements • Nitric acid • colorless, fuming liquid with a pungent odor • decomposes in sunlight: • 4HNO3 --> 4NO2 + 2 H2O + O2 • turns yellow as it ages because of the NO2 • strong oxidizing agent • reacts with metal oxides, hydroxides, and carbonates to form nitrate salts which are generally very soluble in water

49. The Representative Elements • Nitrous Acid • HNO2, a weak acid, forms pale yellow nitrite salts • nitrites are very stable, even at high temperatures • nitrites are prepared by bubbling nitric oxide, nitrogen dioxide, and a metal hydroxide: • NO + NO2 + 2NaOH --> 2NaNO2 + H2O

50. The Representative Elements • The Chemistry of Phosphorus • very different properties from those of nitrogen • due to • N’s ability to form pi bonds • greater electronegativity of N • larger size of P • availability of d orbitals on phosphorus • several solid forms of phosphorus • white phosphorus, P4, with a tetrahedral geometry • very reactive, bursts into flames on contact with air (it is pyrophoric)