Question

Use the ideas of MO theory to explain why the carbide anion has the formula that it does.

Answer 1

molecular orbital (MO) theory is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule. The spatial and energetic properties of electrons within atoms are fixed by quantum mechanics to form orbitals that contain these electrons. While atomic orbitals contain electrons ascribed to a single atom, molecular orbitals, which surround a number of atoms in a molecule, contain valence electrons between atoms.

Calcium carbide, CaC2, is a reactive salt used in a number of industrial processes including the production of acetylene. Use molecular orbital theory to describe the bonding of the carbide anion (C₂^2-).

The complete orbital occupancy (i.e. electron configuration) for carbide anion-
(1σ)² (1σ*)² (2σ)²(2σ*)²(1π)⁴(3σ)²
The bond order for C2^2-is 3. The bond order for C2 is 2. Bond dissociation energy increases with increasing bond order.