Consider the following pairs of atoms. Place each set in order of increasing bond polarity. Describe the trend.

a. Li-F Na-F K-F Rb-F Cs-F

b. Mg-O P-S N-F K-Cl Al-N

a) Answer is: Li-F, Na-F, K-F, Rb-F, Cs-F.

When the electronegativity difference is greater, the bond polarity is increasing ...

Electronegativity (χ) is a property that describes the tendency of an atom to attract a shared pair of electrons.

Atoms with higher electronegativity attracts more electrons towards it, electrons are closer to that atom.

For example fluorine has electronegativity approximately χ = 4 and sodium χ = 0.95, fluorine attracts electron and it has negative charge and sodium has positive charge.

Δχ (Li-F) = 4 - 1 = 3.

Δχ (Na-F) = 4 - 0.95 = 3.05; electronegativity difference between sodium and fluorine.

Δχ (K-F) = 4 - 0.85 = 3.15.

Δχ (Rb-F) = 4 - 0.8 = 3.2.

Δχ (Cs-F) = 4 - 0.75 = 3.25.

b) Answer is: P-S, N-F, Al-N, Mg-O, K-Cl.

Δχ (Mg-O) = 3.5 - 1.3 = 2.2; electronegativity difference between magnesium and oxygen.

Δχ (P-S) = 2.6 - 2.2 = 0.4; electronegativity difference between phosphorus and sulfur.

Δχ (N-F) = 4 - 3 = 1; electronegativity difference between nitrogen and fluorine.

Δχ (K-Cl) = 3.2 - 0.85 = 2.35; electronegativity difference between potassium and chlorine.

Δχ (Al-N) = 3 - 1.6 = 1.4; electronegativity difference between aluminium and nitrogen.