question_answer

Give reasons for the following: (a) \[C{{N}^{-}}\]ion is known but \[C{{P}^{-}}\] ion is not known (b) \[N{{O}_{2}}\]dimerises to form \[{{N}_{2}}{{O}_{4}}\] (c) \[lCl\] is more reactive than \[{{I}_{2}}\].   

Answer:

                                           (a) Carbon and nitrogen atoms have comparable sizes. They can be linked to each other by triple bond to form \[C\equiv \overset{\odot -}{\mathop{N}}\,:\]ion in which \[{{p}_{\pi }}-{{p}_{\pi }}\] bonding is possible. However, similar \[{{p}_{\pi }}-{{p}_{\pi }}\] bonding is not possible between carbon and phosphorus atoms because of comparatively large atomic size of phosphorus. Therefore, \[C\equiv \overset{\odot -}{\mathop{P}}\,:\] ion does not exist. (b) \[N{{O}_{2}}\] is an odd electron molecule and has 17 valence electrons (5 due to N and 12 due to two 0 atoms). Upon dimerisation, it changes into a stable \[{{N}_{2}}{{O}_{4}}\] molecule with even number of electrons (34).     (c) \[\text{ICl}\] is polar \[(\overset{\,\delta +}{\mathop{I}}\,-\overset{\delta -}{\mathop{C}}\,l)\] due to the electro negativity difference between the two participating halogen atoms. It is therefore, more reactive than 12 which is completely non-polar.