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According to Valence Bond Theory (VBT), with the z-axis taken as the molecular (internuclear) axis, which of the following pairs of atomic orbitals results in a nonbonding (zero net overlap) interaction?

1. 1s and 2pₓ
2. 2pₓ and 2pₓ
3. 2p_z and 2p_z
4. 2pₓ and 3d_xz

Correct answer: 1s and 2pₓ

Solution

The 1s orbital is spherically symmetric. When it overlaps with 2pₓ (whose lobes lie perpendicular to the z-axis), the positive overlap with one lobe exactly cancels the negative overlap with the other lobe, giving net overlap = 0. All other listed pairs can produce nonzero net overlap (bonding or antibonding).

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