Download presentation
1
Ch. 19:Representative Elements Groups 1A-4A
2
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
3
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)
4
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
5
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
6
Group 1A- Hydrogen H = most abundant element in the universe 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), 700C, 1300F
7
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) + ….
8
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
9
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
10
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, 5% of all electricity in US! Al is very reactive, forms oxide “skin” that stops reaction
11
Group 4A ns2np2 Silicon Si = 2nd most abundant element in Earth’s crust, oceans, air (26% by mass) Si as oxides (silica, silicates)
12
Group 4A- Carbon C = 2nd most abundant element in human body 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
13
Group 4A- Lead Lead Poisonous!! Lead in gasoline was tetrahedral lead #1 use: batteries
14
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.
15
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)
16
Group 5A cont’d Phosphorus
Biological buffer system:H2PO4- HPO42- + H+ ATP + H2O ADP + HPO42- + Energy Reaction structures
17
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
18
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!
19
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)
20
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
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.