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.
When the electronegativity difference is greater, the bond polarity is increasing.
Δχ(C-H) = 2.5 - 2.1 = 0.4; nonpolar covalent.
Δχ(K-Cl) = 3.0 - 0.8= 2.2; ionic bond.
Δχ(Na-O) = 3.5 - 0.9 = 2.6; ionic bond.
Δχ(Br-Br) = 2.9 - 2.9 = 0; nonpolar covalent.
Δχ(C-F) = 4 - 2.5 = 1.5; polar covalent.
Δχ(Na-F) = 4 - 0.9 = 3.1; ionic bond.
Δχ(H-F) = 4 - 2.1 = 1.9; polar covalent.
Δχ(F-F) = 4 - 4 = 0; nonpolar covalent.
Δχ(Al-Cl) = 3 - 1.6 = 1.4; polar covalent.
Δχ(Br-F) = 4 - 2.9 = 1.1; polar covalent.