Question

The table below shows the electronegativity values of various elements on the periodic table.

Electronegativities
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Which pair of atoms would form a covalent bond ?
calcium (Ca) and bromine (Br)
rubidium (Rb) and sulfur (S)
cesium (Cs) and nitrogen (N)
oxygen (O) and chlorine (Cl)

Answer 1

Use the electronegativity differences. A common cutoff is ~1.7 (Pauling scale): differences larger than this give ionic bonding, smaller give covalent.

- Ca (≈1.0) and Br (≈3.0): Δχ ≈ 2.0 → ionic
- Rb (≈0.8) and S (≈2.6): Δχ ≈ 1.8 → ionic (borderline)
- Cs (≈0.8) and N (≈3.0): Δχ ≈ 2.2 → ionic
- O (≈3.4) and Cl (≈3.2): Δχ ≈ 0.2 → covalent

Therefore oxygen and chlorine would form a covalent bond.