Question

The shape of sulphate ion is

• A. square planar
• B. trigonal
• C. trigonal planar
• D. tetrahedral

Answer 1

Answer: (D)

Sulphate ion $\left(S{O}_4^{2-}\right)$ has tetrahedral geometry as in it S-atom undergoes $s{p}^3$-hybridisation.
The valence shell configuration of $S$ atom and oxygen atom are
$S$-atom (G.S.) $3s^{2}3p_x^{2}3p_y^{1}3p_z^1$
$O$-atom (G.S.) $2s^{2}2p_x^{2}2p_y^{1}2p_z^1$
$O^{-}$ion (G.S.) $2s^{2}2p_x^{2}2p_y^{2}2p_z^1$
$S$-atom in II excited state
$3s^1,3p_x^{1}3p_y^{1}3p_z^{1}3d_{z^2}^{1}3d_{x^2-y^2}^1$

Due to $s{p}^3$-hybridisation four hybrid orbitals are directed towards four corners of tetrahedron. These half filled hybrid orbitals form four sigma bonds $\left[s{p}^3(S)-p(O)\right]$ with four O-atoms and two pi-bonds are formed by $d_{\pi }-p_{\pi }$ overlapping. Thus $S{O}_4^{2-}$ ion has tetrahedral geometry.