16 . Reactivity towards halogen : Group 15 elements form trihalides and pentahalides .
Trihalides – covalent compounds and become ionic down the group .
sp 3 hybridisation , pyramidal shape Pentahalides - sp 3 d hybridisation , TBP shape
They are lewis acids because of the presence of vacant d – orbitals .
PCl5 + Cl - → [ PCl6 ] -
PCl5 is ionic in solid state and exist as [ PCl4 ] + [ PCl6 ] -
In PCl5 , there are three equatorial bonds and two axial bonds . The axial bonds are longer than equatorial bonds because of greater repulsion from equatorial bonds .
Nitrogen does not form pentahalides due to absence of d- orbitals .
17 . Reactivity towards metals : All elements react with metals to form binary compounds in – 3 oxidation state .
18 . Anomalous behaviour of nitrogen : The behaviour of nitrogen differs from rest of the elements .
Reason :
i . It has a small size .
ii . It does not have d – orbitals iii . It has high electronegativity
iv . It has high ionization enthalpy