JEE Main 2021 · 25 July · morning · Single correct · +4 / −1
Which one of the following compounds of Group-14 elements is not known?
- (a) [GeCl₆]²⁻
- (b) [Sn(OH)₆]²⁻
- (c) [SiCl₆]²⁻
- (d) [SiF₆]²⁻
Answer and solution
Answer (c) [SiCl₆]²⁻
Solution
Chemistry ma’am · 3 steps
Silicon fits six small F atoms around it, but not six large Cl atoms.
- Room for six. Each of these ions has six groups around the central atom. The central atom must be able to use more than four orbitals, and it must have enough space around it for six ligands.
- Size decides. Silicon is small. Six small F atoms fit around it, but six large Cl atoms crowd each other too much. The lone pairs on Cl also interact weakly with Si, so Cl does not bind well to Si.
Ion Central atom Ligand Known? [GeCl₆]²⁻ Ge, larger Cl yes, Ge is big enough [Sn(OH)₆]²⁻ Sn, larger still OH⁻, small yes, stannate ion [SiCl₆]²⁻ Si, small Cl, large no [SiF₆]²⁻ Si, small F, small yes, hexafluorosilicate - So. The ion that is not known is [SiCl₆]²⁻, option (c).
The idea to keep. For six groups around a Group 14 atom, check two sizes: is the centre big enough, and are the ligands small enough? Si holds six F, never six Cl.
Answer from the NTA final answer key. Solution by PrepWiser.