Electronegativity Difference And Bond Character Page 2
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4Problem Set on Bonding
Electronegativity Difference and Bond Character
Covalent bond - a shared pair of electrons between two atoms
Electronegativity - the ability of an atom to attract electrons in a covalent bond.
Electronegativity Difference, E,
E = E
-E
,
1
2
E = E
For example, each H—–O bond in H
O has:
- E
2
O
H
E = 3.44 - 2.10
E = 1.44
As the electronegativity difference grows from 0.00 to >3.00, the sharing of electrons becomes more skewed. First one atom
becomes partially negative, -, while the other becomes partially positive, +, and the bond is polarized, a polar covalent bond.
Then as the sharing becomes more and more unequal, the electrons reside only on one atom. The atoms are now ionized (+ or -
), and the bond is called ionic. This is shown in Table 1.
↔
↔
Table 1
nonpolar covalent
polar covalent
ionic
Electronegativity
0.00
0.65
0.94
1.19
1.43
1.91
2.19
2.54
3.03
1.67
Difference, E
0%
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
Percent Ionic Character
Percent Covalent
100 % 90 %
80 %
70 %
60 %
50 %
40 %
30 %
20 %
10 %
Character
For a shared pair of electrons, if one atom is able to attract the electrons to itself (more electronegative) that atom will
begin to become negatively charged,
-
, (a negative pole) while the other atom (least electronegative) begins to become
positively charge, +, (a positive pole). The two atoms become a dipole (meaning 2 poles), and the bond will become a polar
covalent bond. [see Table 2]
If the difference in attracting the electrons, E, is so great, then one atom may just take the electrons for itself. This
stops any sharing of electrons, and the bond is an ionic bond. The atom that took the electrons is the anion (negative), and the
atom that lost the electrons is the cation (positive). [see Table 2]
If the difference in attracting the electrons, E, is very small, then the sharing remains relatively equal and no charges
develop. No developed charges means there are no pole, which makes the bond a nonpolar covalent bond. In the special case
that the electronegativity difference, E, is zero, then no atom attracts the electrons to itself and the sharing is perfectly equal.
Such a bond is called a pure covalent bond and is nonpolar also. [see Table 2]
Table 2
Electronegativity Difference, E
Polarity
Bond Type
E = 0.00
nonpolar
pure covalent
0.00 < E < 0.65
nonpolar
nonpolar covalent
0.65 < E < 1.67
polar
polar covalent
1.67 < E
ionic
More on Dipoles
An electric dipole consists of two opposite charges that are the same magnitude and separated in space.
Unequal sharing of electrons (E > 0) results in one end of the bond being negative and one end being positive. This
is a dipole (2 poles, one negative, one positive)
The atom with the greater electronegativity becomes partially negative, -,
The atom with the smaller electronegativity becomes partially positive, +.
Drawing an arrow from + to - shows the electric field between the charges.
Practice Problem: Hydrogen fluoride, HF
o
Draw the Lewis Structure
o
Determine the polarity and bond type for each bond.
o
Draw the dipole for each bond.
HF, would be written as
H—– F
Since E = 1.10, the bond is polar covalent.
E = 3.98 - 2.10 = 1.10}
F has the greater electronegative so it is partially negative, -, and H with the smaller electronegativity is partially
positive, +.
H —– F
Final Answer:
+ → - polar covalent
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