Explain how you can predict whether a diatomic molecule will be polar.

By using an electronegativity table (a periodic table with electronegativity values), you can find the difference between the two elements of the molecule and then determine its polarity based on the following criteria:

Nonpolar Covalent Bond: < 0.4

Polar Covalent Bond: between 0.4 and 1.8

Ionic Bond: > 1.8

Example:

Let's we are given the diatomic molecule, HCl.

Electronegativity of H: 2.1

Electronegativity of Cl: 3.0

Find the difference by subtracting the smaller value from the bigger one:

3.0 - 2.1 = 0.9

0.9 is between 0.4 and 1.8; thus it is a polar covalent bond.