Chemistry Reference
In-Depth Information
electronegativity of 4.0. The electronegativity values for the elements in
the main body of the periodic table are shown in Figure 4-1a.
Electronegativities of Selected Elements
H
2.2
Li
1.0
Na
0.9
K
0.8
Rb
0.8
Cs
0.7
Be
1.5
Mg
1.2
Ca
1.0
Sr
1.0
Ba
0.9
B
2.0
Al
1.5
Ga
1.6
In
1.7
Tl
1.8
C
2.6
Si
1.9
Ge
1.9
Sn
1.8
Pb
1.8
N
3.1
P
2.2
As
2.0
Sb
2.1
Bi
1.9
O
3.5
S
2.6
Se
2.5
Te
2.3
Po
2.0
F
4.0
Cl
3.2
Br
2.9
I
2.7
At
2.2
Figure 4-1a
When atoms with very different electronegativities combine, they tend
to form bonds with a high degree of ionic character, which means that the
sharing of electrons is so unequal that the electrons can effectively be
thought to be in the possession of one atom. This “stealing” of electrons
results in one atom having extra electrons and a net negative charge, and
another atom, which is missing electrons, having a net positive charge. Each
pair of such ions are held together by the electrostatic force of attraction
between unlike charges, which is called an ionic bond.
Bonds formed between atoms with relatively little or no difference in
electronegativity show a high degree of covalent character, meaning that
the sharing of electrons is closer to equal. When we say that atoms share a
pair of electrons, we don't mean that they necessarily share them 50/50. It
is possible, for example, that the pair of shared electrons will spend ap-
proximately 70% of the time in one atom's electron cloud and only 30% of
the time in the other atom's electron cloud. How equal the sharing of the
electrons is depends on the difference in the electronegativiy values of
the elements involved. If the difference in electronegativity between the
bonding atoms is very low, then a non-polar covalent bond is formed,
which means that the atoms share the electrons essentially equally. If the
