Structural Biochemistry/Electronegativity

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File:Electronegativity Scale.png
Scale of electronegativity trends

Electronegativity[edit]

Electronegativity increases going up the periodic table and to the right of it. Meaning the most electronegative atom is Fluorine and the least electronegative atom is Cesium. What electronegativity means is the ability of an atom to attract electrons. For example, in a H-Cl bond, Cl is more electronegative than H. Therefore, the electrons will be closer to Cl.

Besides, because the nucleus of a smaller atom is closer to the shared pair than that of a larger atom, it attracts the bonding electrons more strongly. The electronegativity is inversely related to atomic size. In generaly, the nonmetals are more electronegativity than the metals. One of the important uses of electronegativity is determining the oxidation number of an atom. The atom's electronegativity refers to its ability to pull bonded electrons towards it. The greater the change in the electronegativity for the two atoms in a bond, the more polar the bond is and also the greater its ionic character.


Reference
http://en.wikipedia.org/wiki/Electronegativity

Electronegativity is the ability of an atom in a molecule to attract a shared electron pair to itself, forming a polar covalent bond. The negative side of a polar covalent bond corresponds to the more electronegative element. In addition, the more polar a bond, the larger the difference in electronegativity of the two atoms.

There is no direct way of measuring electronegativity. Dipole-moment measurements tell us about the electrical behavior of all electron pairs in the molecule, not just the bonding pair in which we are interested. Also, the polarity of a bond depends on whether the bond is a single, double, or triple bond and on what the other atoms and electron pairs in a molecule are. Therefore, the dipole moment cannot tell us quantitatively the difference between the electronegativities of two bonded atoms.

Metals are the least electronegative of the elements.

History[edit]

Electronegativity was first introduced by Pauling in the 1930s to describe bond energies. Pauling's calculations of electronegative from bond energies requires averaging over a number of compounds to cancel out experiemental errors. Jaffe used this idea to develop a theory of the electronegativity of orbitals rather than just atoms.

Template:Periodic table (electronegativity by Allen scale)

Number Symbol Name Electronegativity
1 H hydrogen 2.300
2 He helium 4.160
3 Li lithium 0.912
4 Be beryllium 1.576
5 B boron 2.051
6 C carbon 2.544
7 N nitrogen 3.066
8 O oxygen 3.610
9 F fluorine 4.193
10 Ne neon 4.789
11 Na sodium 0.869
12 Mg magnesium 1.293
13 Al aluminium 1.613
14 Si silicon 1.916
15 P phosphorus 2.253
16 S sulfur 2.589
17 Cl chlorine 2.869
18 Ar argon 3.242
19 K potassium 0.734
20 Ca calcium 1.034
21 Sc scandium 1.19
22 Ti titanium 1.38
23 V vanadium 1.53
24 Cr chromium 1.65
25 Mn manganese 1.75
26 Fe iron 1.80
27 Co cobalt 1.84
28 Ni nickel 1.88
29 Cu copper 1.85
30 Zn zinc 1.59
31 Ga gallium 1.756
32 Ge germanium 1.994
33 As arsenic 2.211
34 Se selenium 2.434
35 Br bromine 2.685
36 Kr krypton 2.966
37 Rb rubidium 0.706
38 Sr strontium 0.963
39 Y yttrium 1.12
40 Zr zirconium 1.32
41 Nb niobium 1.41
42 Mo molybdenum 1.47
43 Tc technetium 1.51
44 Ru ruthenium 1.54
45 Rh rhodium 1.56
46 Pd palladium 1.59
47 Ag silver 1.87
48 Cd cadmium 1.52
49 In indium 1.656
50 Sn tin 1.824
51 Sb antimony 1.984
52 Te tellurium 2.158
53 I iodine 2.359
54 Xe xenon 2.582
55 Cs caesium 0.659
56 Ba barium 0.881
71 Lu lutetium 1.09
72 Hf hafnium 1.16
73 Ta tantalum 1.34
74 W tungsten 1.47
75 Re rhenium 1.60
76 Os osmium 1.65
77 Ir iridium 1.68
78 Pt platinum 1.72
79 Au gold 1.92
80 Hg mercury 1.76
81 Tl thallium 1.789
82 Pb lead 1.854
83 Bi bismuth 2.01
84 Po polonium 2.19
85 At astatine 2.39
86 Rn radon 2.60
87 Fr francium 0.67
88 Ra radium 0.89

References[edit]

Miessler, Gary. Inorganic Chemistry. 4th Edition.