Question

Explain the following terms:
(i) Crystal field splitting in an octahedral field
(ii) Spectrochemical series.

Answer 1

(i) Crystal field splitting in an octahedral field.
According to C.F.T at first there is an increase in the energy of d-orbitals relative to that of the free ion just as would be the case in spherical field. The two orbitals lying along the axis get repelled more strongly than other three (d_xy, d_yz, d_xz). The degenerate set of d-orbitals get split into two sets: the lower energy t_2g set and e_g set. The energy separation is denoted by ∆_o . The actual configuration adopted is decided by the relative values of ∆_o and P. P-represents the energy required for electron pairing in a single orbital. (a) If ∆_o < P then fourth electron goes to e_g

(a) If ∆_o < P then fourth electron goes to eg

(b) When ∆_o > P, then fourth electron pairs the t_2g orbital.

(ii) Spectrochemical Series: It is a series in which ligands can be arranged in the order of increasing field strength or in order of increasing magnitude of splitting they produce. The order is