Question

give reason

SiF6^2- exists while CF6^2- does not.

Answer 1

carbon have not any vacant d orbital while silicon have 3d lower energy vacant orbital .

according to Lewis second period elements can not expands your octate because elements have not any d and f orbits .

also size of carbon is very small so that carbon can not take six long paires from fluorine.

this is unstable and here long pair replustion is very high .

but in silicon have d orbits .
fluorine give long pair in silicon 3d orbits so that silicon have expended your orbits .

here size of silicon is not too small
so that fluorines gives there long pair easily .

therefore SiF6²- exist while CF6²- does not exist .

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