Answer:
For example, a water molecule (H2O) has a large permanent electric dipole moment. Its positive and negative charges are not centered at the same point; it behaves like a few equal and opposite charges separated by a small distance.
Any molecule that has a nonzero vector sum of dipole moments is said to be polar and have a dipole moment
Explanation:
A dipole moment refers to slight opposite charges on opposite sides of a bond. The resulting bond is said to be polar; it has a positive pole and a negative pole, much like a bar magnet.
In order to determine if a particular bond is polar or not, one must look for the electronegativity of each atom. Pauling's electronegativity is a measure of how strong a particular atom pulls electrons towards it in a bond. The value of the difference between their electronegativities (
Δ
E
N
) determines how polar a bond is.
If:
0
≤
Δ
E
N
≤
0.4
, the bond is nonpolar.
0.4
<
Δ
E
N
≤
1.8
, the bond is polar
Δ
E
N
>
1.8
, the bond is ionic
Consider the bonds in
There is one oxygen bonded to two hydrogens in one water molecule. Based on the difference in electronegativites for the bonds, it is clearly a polar molecule
E
N
O
=
3.44
E
N
H
=
2.20
Δ
E
N
=
3.44
−
2.20
=
1.24
In the figure above, the δ symbol indicates an area of partial charge on the atom. Note that they are not full charges as in ions, but partial charges due to a difference in electron density at each "pole". The arrow in the figure indicates the direction of electron density and the slight negative charge
δ
−
and the cross indicates an area of electron deficiency and the slight positive charge δ
+
. This difference in charges is called a dipole moment and it is a vector quantity; it has magnitude and direction.
Notice that the water molecule has an overall dipole moment that points straight up towards the oxygen. This is because a dipole moment of a molecule depends on the vector sum of the bond dipoles.
Consider C
O
2
,
As you can see, the Δ
E
N for the C
−
O bond is within the polar range. However, since C
O
2 is a linear molecule, the dipoles point in opposite directions and the vector sum of the two is equal to zero. C
O
2
is nonpolar.
