4.3 ELECTRONEGATIVITY AND BOND POLARITY

is a measure of an atom’s
ability
within a
covalent bond. It is the property of an atom.

developed electronegativity values
that range from 0.7 (cesium) to 4.0 (fluorine) this concept as a
method to determine the bonding appropriate for various elements.
Due to various restrictions on the abundance and nature of various
elements, some values for electronegativity have been under review.
PERIODIC TREND OF ELECTRONEGATIVITY
Across a Period from Left to Right:
Electronegativity
REASONS:
Down a Group:
Electronegativity
REASONS:
ELECTRONEGATIVITY AND BONDING
 The
between two atoms helps us decide whether a bond is
considered ionic or covalent. All bonds are essentially a mixture of
and
character.
 The type of bond can be determine by calculating the
.
Electronegativity 0.00
Difference
Percent Ionic
0%
Character
Percent Covlaent 100%
Character
0.65
0.94
1.19
1.43
1.67
1.91
2.19
2.54
3.03
10%
20%
30%
40%
50%
60%
70%
80%
90%
90%
80%
70%
60%
50%
40%
30%
20%
10%
THE BONDING CONTINUUM
IONIC BONDS
 Electronegativity Difference (EN):
 One of the atoms has a much stronger attraction for the bonding
electrons than the other atom.
 The electrons are pulled completely away from the atom with the
forming a
and transferred to the
atom with the
forming an
.
 The negative and positive charges are attracted to each other by
.
NON-POLAR COVALENT BONDS:
 Electronegativity Difference (EN):
 Both atoms have an
to share the bonding
electrons.
 The bond is uncharged
 These bonds usually occur between atoms of the same elements
(
).
POLAR COVALENT BONDS:
 Electronegativity Difference (EN):
 One of the atoms has a significantly stronger attraction for the
shared electrons.
 The electrons are shared
among the
atoms.
 The electrons are shifted closer to the atoms with the
forming a
charge and
shifted away from the atom with the
forming a
charge.
 When you place molecules (that consist of a polar covalent bond) in an electric field (created
from two charged plates), they will move in accordance to the slight charges each atom in
the molecule possesses.
 The polarity of the bond influences the physical and chemical properties of molecules.
The diagram to the right is an example of a
,
which shows a direction in electron density that results in the
formation of positive and negative charges in a region of space.
The arrow is always drawn in the direction of the negative end,
and the tail (resembling a positive charge) is always drawn near
the positive end.
HOMEWORK: Read Page 217-220 and do Page 221 #1-10