Question

What is hybridisation? Explain the formation of the following molecules using hybridisation a) BeCl2 b) BF3

Answer 1

Be is the central atom here. Its electronic configuration is 1s^22s^2, showing two electrons in its valence shell. Two chlorine atoms are bound to it via single covalent bonds. Hence total electron count around the central atom becomes 2+2 = 4 electrons or, two pairs. There is no possibility of a lone pair in the molecule. Hence, according to valence shell electron pair repulsion (VSEPR) calculations, X, the co-ordination number for central atom, should be 2. This implies that the hybridization must be sp; supporting a linear geometry for BeCl2 molecule, with a bond angle of 180 degrees.

Boron trifluoride (BF3) has a boron atom with three outer-shell electrons in its normal or ground state, as well as three fluorine atoms, each with seven outer electrons. One of the three boron electrons is unpaired in the ground state. In order to explain the bonding, the 2s orbital and two of the 2p orbitals (called sp2 hybrids) hybridize; one empty p-orbital remains.