Polar Covalent Bonds

Trends in the Periodic Table and Bonding

Covalent Bonding

A covalent bond is a shared pair of electrons electrostatically attracted to the positive nuclei of

two atoms.

The atoms achieve a stable outer electron arrangement (a noble gas arrangement) by

sharing electrons.

-+ +-

-+ +-

Both nuclei try to pull the electrons towards themselves

This is like a tug-of-war where both sides are pulling on the same object.

It creates a strong bond between the two atoms.

Covalent Bonding

Picture a tug-of-war:

If both teams pull with the same force the mid-point of the rope will not move.

Pure Covalent Bond

This even sharing of the rope can be compared to a pure covalent bond, where the bonding pair of electrons are held at the mid-point between the nuclei of the bonding atoms.

H He

e

Covalent Bonding

What if it was an uneven tug-of-war?

The team on the right are far stronger, so will pull the rope harder and the mid-point of the rope will move to the right.

Polar Covalent Bond

A polar covalent bond is a bond formed when the shared pair of electrons in a covalent bond are not

shared equally.

This is due to different elements having different electronegativities.

Polar Covalent Bond

e.g. Hydrogen Iodide

If hydrogen iodide contained a pure covalent bond, the electrons would be shared equally as shown

above. However, iodine has a higher electronegativity and pulls the bonding electrons towards itself(winning the tug-of-war)

This makes iodine slightly negative and hydrogen slightly positive. This is known as a dipole.

H Ie

e

δ-δ+

Polar Covalent Bond

In general, the electrons in a covalent bond are not equally shared.

e.g.

δ- indicates where the bonding electrons are most likely to be found.

2.5 3.0

C Cl

Electronegativities

δ-δ+

Polar Covalent BondConsider the polarities of the following bonds:

Bond

Increasing Polarity

Electronegativities Difference

O H

C Cl

P H

2.5 3.0

3.5 2.1 1.4

0.5

0

P H C Clδ-δ+

O Hδ- δ+

Complete a similar table for C-N, C-O and P-F bonds.

2.2 2.2