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Discuss reactivity of group 14 elements towards water and halogens. |
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Answer» SOLUTION :Reactivity towards water: Carbon, silicon and germanium are not affected by water. Tin decomposes steam to form dioxide and dihydrogen gas. `Sn+2H_2O OVERSETDELTATO SnO_2 + 2H_2` Lead is unaffected by water probably because of protective oxide film formation. Reactivity towards halogen : These elements can form halides of formula `MX_2` and `MX_4` (where X=F,Cl,Br,I) Except carbon, all other members react directly with halogen under suitable condition to make halides. Most of the `MX_4` are covalent in nature. The central metal atom in these halides undergoes `sp^3` hybridisation and the molecule is tetrahedral in shape. Exceptions are `SnF_4` and `PbF_4`,which are ionic in nature. `PbI_4` does not exist because Pb-I bond initially formed during the reaction does not release enough energy to unpair `6s^2` electrons and excite one of them to higher orbital to have four unpaired electrons around lead atom. Heavier members Ge to Pb are able to make halides of formula `MX_2` Stability of dihalides INCREASES down the group. Considering the thermal and chemical stability, `GeX_4` is more stable than `GeX_2` where as `PbX_4` is more than `PbX_4` except `C Cl_4` other tetrachlorides are easily HYDROLYSED by water because the central atom can accommodate the lone pair of electrons from oxygen atom of water molecule in d-orbital. HYDROLYSIS can be understood by taking the example of `SiCl_4`. It undergoes hydrolysis by initially accepting lone pair of electrons from water molecule in d-orbitals of Si, finally leading to the formation of `Si(OH)_4` as shown below : 
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