Short Answer Type
Long Answer TypeGive the points of resemblance and points of difference between valence bond theory and molecular orbtial theory.
Points of resemblance: According to both the theories:
(i) The bond results from the overlap of atomic orbitals.
(ii) The atomic orbitals overlapping each other must be the same energy and must have the same symmetry.
(iii) The electron charge resides in the region between the atomic nuclei.
(iv) Both are approximate theories.
(v) Account the directional character of covalent bonds.
(vi) Predict the non-existence of helium molecule (He2) and neon molecule (Ne2).
(b) Points of difference:
| Valence Bond theory | Molecular Orbital Theory |
| 1. Electrons in molecules are localised as if they are in isolated atoms. | 1. It treats the nuclei of the molecules as polycentric and then constructs the molecular orbitals. |
| 2. Atomic orbitals of participating atoms retain their individual character to a large extent. | 2. Atomic orbitals of the participating atom lose their individual character. |
| 3. It fails to explain paramagnetism of O2. | 3. It explains the paramagnetism of O2. |
| 4. Resonance is an important part of valence bond theory | 4. Resonance has no role in this theory. |
| 5. It is simple to apply. | 5. It is more difficult to apply. |
| 6. It fails to explain the possibility and existence of H2+ | 6. It explains the possibility and existence of H2+ |
Short Answer TypeNitrogen and chlorine have the same electronegativity but only former shows intermolecular hydrogen bonding. Discuss.
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