1. Trends in the Periodic Table and Bonding
Polar Covalent Bonds

2. Covalent Bonding
A covalent bond is a shared pair of electrons electrostatically attracted to the positive nuclei of two atoms.
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.
The atoms achieve a stable outer electron arrangement (a noble gas arrangement) by sharing electrons.

3. Covalent Bonding Picture a tug-of-war:
If both teams pull with the same force the mid-point of the rope will not move.

4. Pure Covalent Bond H e H
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.

5. 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.

6. 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.

7. Polar Covalent Bond I δ- δ+ H e.g. Hydrogen Iodide e
If hydrogen iodide contained a pure covalent bond, the electrons would be shared equally as shown above.
This makes iodine slightly negative and hydrogen slightly positive. This is known as a dipole.
However, iodine has a higher electronegativity and pulls the bonding electrons towards itself
(winning the tug-of-war)

8. Polar Covalent Bond C Cl δ+ δ-
In general, the electrons in a covalent bond are not equally shared. δ- δ+
e.g. C Cl
2.5
3.0
Electronegativities
δ- indicates where the bonding electrons are most likely to be found.

9. Polar Covalent Bond Consider the polarities of the following bonds:
Electronegativities
Difference
C Cl
0.5
P H
O H
1.4
C Cl δ- δ+
O H δ- δ+
P H
Increasing Polarity
Complete a similar table for C-N, C-O and P-F bonds.