C and Si are always tetravalent , but Ge...

`C` and `Si` are always tetravalent , but Ge, Sn and Pb show divalency Give reason .

Text Solution

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Among the elements of group 14, carbon does not have d- or f-electrons . Therefore , it does not show inert pair effect. Consequently, it shows an oxidation state of`+4`due to the presence of two electrons in the s- and two electrons in the p-orbital of the valence shell. In contrast , all other elements from Ge to Pb contain either dor both d- and f-electron increases, the inert pair effect becomes more and more prominent. In other words, as we move dow the group from Ge to Pb, the stability of +2 oxidation state increases while that of `+4` oxidation state decreases. Therefore , the tendency of Ge, Sn and Pb to exhibit +2 oxidation state increases with increasing atomic number in group 14.

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The stability of ions of Ge Sn and Pb will be in the order .

`Ge^(2+) lt Sn^(2+) lt Pb^(2+)`

`Pb^(2+) gt Pb^(4+)`

`Sn^(4+) gt Pb^(2+)`

`Ge^(4+) lt Sn^(4+) lt Pb^(4+)`

Catention properties of C, Si, Ge, Sn , Pb are in order

`C gt gt Si gt Ge ~~ Sn gt gt Pb`

`C lt Si lt Ge lt Sn lt Pb`

`C gt Si gt Sn gt Ge gt Pb`

none is correct

Assertion (A) : C,Si and Ge have 4 Valancy each both but C is an insulator where as Si and Ge are semi conductors Reason ( R) : Energy gap is least for Ge , less for Si compared to C , So that free electrons for conduction in Ge and Si are significant but negligible small for C .

`A,R` are true and `R` explains `A` correctly

`A,R` are true and `R` do not explain `A` correctly

`A` is true, but `R` is false

`R` is true, but `A` is false