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Monday, December 29, 2014

Valences of the Elements

Chemistry of the Periodic Table
Many people believe that the valences of the elements are those which can be derived by looking at the Groups (columns) of the Periodic Table. It is true that these are the most common valences, but the real behavior of electrons is less simple. Here is a listing of element valences. Remember that an element's electron cloud will become more stable by filling, emptying, or half-filling the shell. Also, shells don't stack neatly one on top of another, so don't always assume an element's valence is determined by the number of electrons in its outer shell.
NumberElementValence
1Hydrogen(-1), +1
2Helium0
3Lithium+1
4Beryllium+2
5Boron-3, +3
6Carbon(+2), +4
7Nitrogen-3, -2, -1, (+1), +2, +3, +4, +5
8Oxygen-2
9Fluorine-1, (+1)
10Neon0
11Sodium+1
12Magnesium+2
13Aluminum+3
14Silicon-4, (+2), +4
15Phosphorus-3, +1, +3, +5
16Sulfur-2, +2, +4, +6
17Chlorine-1, +1, (+2), +3, (+4), +5, +7
18Argon0
19Potassium+1
20Calcium+2
21Scandium+3
22Titanium+2, +3, +4
23Vanadium+2, +3, +4, +5
24Chromium+2, +3, +6
25Manganese+2, (+3), +4, (+6), +7
26Iron+2, +3, (+4), (+6)
27Cobalt+2, +3, (+4)
28Nickel(+1), +2, (+3), (+4)
29Copper+1, +2, (+3)
30Zinc+2
31Gallium(+2). +3
32Germanium-4, +2, +4
33Arsenic-3, (+2), +3, +5
34Selenium-2, (+2), +4, +6
35Bromine-1, +1, (+3), (+4), +5
36Krypton0
37Rubidium+1
38Strontium+2
39Yttrium+3
40Zirconium(+2), (+3), +4
41Niobium(+2), +3, (+4), +5
42Molybdenum(+2), +3, (+4), (+5), +6
43Technetium+6
44Ruthenium(+2), +3, +4, (+6), (+7), +8
45Rhodium(+2), (+3), +4, (+6)
46Palladium+2, +4, (+6)
47Silver+1, (+2), (+3)
48Cadmium(+1), +2
49Indium(+1), (+2), +3
50Tin+2, +4
51Antimony-3, +3, (+4), +5
52Tellurium-2, (+2), +4, +6
53Iodine-1, +1, (+3), (+4), +5, +7
54Xenon0
55Cesium+1
56Barium+2
57Lanthanum+3
58Cerium+3, +4
59Praseodymium+3
60Neodymium+3, +4
61Promethium+3
62Samarium(+2), +3
63Europium(+2), +3
64Gadolinium+3
65Terbium+3, +4
66Dysprosium+3
67Holmium+3
68Erbium+3
69Thulium(+2), +3
70Ytterbium(+2), +3
71Lutetium+3
72Hafnium+4
73Tantalum(+3), (+4), +5
74Tungsten(+2), (+3), (+4), (+5), +6
75Rhenium(-1), (+1), +2, (+3), +4, (+5), +6, +7
76Osmium(+2), +3, +4, +6, +8
77Iridium(+1), (+2), +3, +4, +6
78Platinum(+1), +2, (+3), +4, +6
79Gold+1, (+2), +3
80Mercury+1, +2
81Thallium+1, (+2), +3
82Lead+2, +4
83Bismuth(-3), (+2), +3, (+4), (+5)
84Polonium(-2), +2, +4, (+6)
85Astatine?
86Radon0
87Francium?
88Radium+2
89Actinium+3
90Thorium+4
91Protactinium+5
92Uranium(+2), +3, +4, (+5), +6

Reference: Lange's Handbook of Chemistry, 8th Ed., Norbert A. Lange (Ed.), Handbook Publishers, Inc. 1952.

Wednesday, December 3, 2014

I can never forget this great man

While I was struggling to find out a method related to spectroscopic technique in Computational Chemistry, many Indian Scientists deliberately delayed disclosing the same for reasons better known to them. Quite reluctantly I just shot a mail to PvR Schleyer (on whose references I built up my PhD thesis) and wanted to forget the whole episode of requesting with our fellows. And to my surprise, I got a reply from him in minutes!!! He did not know me, but for the sake of 'humanity', perhaps, he elaborated the technique with an example!

He has died a few days back, on 21st November, at his home in Ila, Georgia, US.

He has published 1271 papers and is the third most cited Chemist in the world of Modern day chemistry. Paul von Ragué Schleyer, 84, a towering figure in physical organic chemistry and a chemistry professor at the University of Georgia, in Athens is no more.

Delving into a broad range of physical organic, organo-metallic, inorganic, and theoretical chemistry topics, Schleyer made vast contributions, including discovering ways of synthesizing adamantane and other cage molecules by rearrangement. He also identified new types of hydrogen bonding, elucidated solvolysis mechanisms, and expounded on the nature of reactive intermediates.

Schleyer discovered new molecular structures, particularly those involving lithium and electron-deficient systems. Most recently, he focused on nuclear magnetic resonance, aromaticity, and planar hypercoordination of carbon and other elements.

His home page: http://schleyer.chem.uga.edu/