Ch. 19:Representative Elements Groups 1A-4A

Representative Elements Groups 1A  8A Chemical properties determined by valence electrons in level s & p Transitions metals (center of table) Result from filling d- orbitals Lanthanides & Actinides -- result from filling of 4f and 5f orbitals respectively

Heavy black line divides the metals from nonmetals Elements on either side of line exhibit metallic AND nonmetallic properties These are called metalloids or semimetals (Si, Ge)

Big Ideas Representative Elements a. Same column, same family, similar chemical properties b. Typically, FIRST element is most different than the others H, Be, B, C, N, O, F c. Metallic properties increase down column(esp 4A) d. Other properties vary regularly up/down column e. Majority of naturally occurring elements are in compounds

Group 1A ns1 valence e- Easily lose valence e- (except for hydrogen) Alkali Metals Form M+ cations React vigorously with H2O to form M+ and OH- ions AND H2 gas

Group 1A- Hydrogen H = most abundant element in the universe (@3/4 of all mass!) H2 (g) is rare in Earth’s atmosphere H = 3rd most abundant element in human body (10% by mass) Commercial production of H2 from methane (CH4), water@ 700C, 1300F

Group 1A cont’d Metals (Li, Na, K…), Alkali Metals Form oxides/hydrides that are all basic in water; (Metal + H2O  OH- (aq)… NaH (hydride)  H2(g) + …. Na2O (oxide) Na2O2 (peroxide) NaO2 (superoxide)  O2(g) + ….

Group 2A ns2 Oxides are also basic in water; Metal + H2O  OH-(aq)…. Ca2+ & Mg2+ are most common metals in human body Ca2+ & Mg2+ are most common ions I “hard” water Ca2+ precipitates fluoride out of water (Ksp = 4x10-11) Marble CaCO3, converted to CaSO4 by acid rain

Group 3A ns2np1 Shows increasing metallic character moving down the group Boron-hydrogen covalent compounds = “boranes” VERY reactive, electron deficient Unusual B-H-B bonds (fig 19.8, p889) example

Group 3A-Aluminum Al = 3rd most abundant element in Earth’s crust, oceans, air (8% by mass) Al = most abundant metal on earth (Al2O3) Expensive to recover, consumes @ 5% of all electricity in US! Al is very reactive, forms oxide “skin” that stops reaction

Group 4A ns2np2 Silicon Si = 2nd most abundant element in Earth’s crust, oceans, air (26% by mass) Si as oxides (silica, silicates)

Group 4A- Carbon C = 2nd most abundant element in human body (@18%) Carbon- Diamond Carbon-Graphite Carbon monoxide bonds to hemoglobin 100x more than oxygen Carbon dioxide dissolved in water is acidic Sugar (CH2O) ferments with yeast to form ethanol

Group 4A- Lead Lead Poisonous!! Lead in gasoline was tetrahedral lead #1 use: batteries

Ch 20 –Group 5A Nitrogen 1. N2 = most abundant element in air(78% by volume) 2. Very unreactive as N2; triple bonded 3. Nitrogen fixation: N2  compounds containing N (bacteria, human activity) a. “fixed” nitrogen encourages algae growth b. amount of “fixed” nitrogen is currently increasing.

Nitrogen cont’d a. airbags b. Trinitrotoluene, TNT and nitroglycerin 4. Explosives: Many compounds with N (+H, C, and/or O)  N2, H2O and/or CO2 gases –EXOTHERMIC! a. airbags b. Trinitrotoluene, TNT and nitroglycerin 5. Smog; at high T& P: N2 +O2  2NO (in air  NO2 = brown gas)

Group 5A cont’d Phosphorus Biological buffer system:H2PO4-  HPO42- + H+ ATP + H2O  ADP + HPO42- + Energy Reaction structures

Group 6A Ozone = O3 2. highly toxic; antibacterial properties Group 6A-Oxygen O = most abundant element in human body O = most abundant element in earth’s crust, oceans, air (49% by mass) O2 = 2nd most abundant element in air (21% by volume) Ozone = O3 1. ozone layer absorbs U.V. light in upper atmosphere 2. highly toxic; antibacterial properties

Group 6A cont’d Sulfur Acid rain: 1. S (fuel, esp. Diesel & Coal) + O2  SO2 2. SO2 + O2  SO3 (catalyzed by dust & particles in air) 3. SO3 + H2O  H2SO4! ACID rain ! Selenium & cancer ? Polonium alpha particle emitter; murdered Russian ex-spy Litvinenko chemically like Oxygen!

Group 7A Halogens I. Found in nature as X2 or X- II. X + X  X2 (quickly) III. Strong oxidizers; want to remove electrons from other atoms: Cl + Cu+ -- Cl- + Cu2+ Fluoride 1. strong acids: HCL, HBr, HI, but NOT HF 2. Generally soluble in salts: chlorides, bromides, but NOT Fluorides 3. Entropy does not favor F-(aq)

Group 8A “Noble Gases” a. generally unreactive; NO compounds containing He, Ne, or Ar b. recently, found compounds of Xe and Kr with F and O