Chemical Properties Chemistry Notes
Chemical Properties :
Anomalous Behaviour of Nitrogen :
Nitrogen show anomalous behaviour and differs from other members of his family. The main reasons for showing this anomalous behaviour is as follow:
- Its atomic size is exceptionally small.
- It has very high electronegativity.
- It has very high ionisation enthalpy.
- It does not have vacant d-orbitals in its valance shell.
- It has tendency to form multiple bonds.
→ Some other anomalous properties of nitrogen are as follows:
- Nitrogen is gas while the other members are solids.
- Nitrogen molecule is diatomic (N ≅ N) while other members are tetra atomic molecules. For example P4, As4, Sb4 etc.
→ Reason : Nitrogen atom has small size, high electronegativity and unique property to form PT – ppt multiple bonds with itself and with other small sized and highly electronegative elements like oxygen, carbon etc. Thus, nitrogen forma diatomic molecule (N2).
→ In nitrogen molecule there is a triple bond with one sigma (σ) and two-bonds. There nitrogen molecules are held together by weak London forces (i.e. van der Wall’s forces) which can be broken easily by collision at room temperature. Hence, nitrogen molecule (N) is a gas at room temperature. On the other hand, other elements of nitrogen family i.e.
→ phophorus, arsenic antimony etc. form tetrahedral molecules (E4) in their elemental state. Because they can not form pπ – pπ multiple bonding due to their large atomic size bonds and exist as discrete tetra-atomic tetrahedral molecules. These molecules have strong forces of attraction and hence exist as solid at room temperature.
- The last element bismuth (Bi) forms metallic bonds in the elemental state.
- Except NF, other halides of nitrogen ie, NCIE, NBr., NI, are unstable while trihalides of other members of this family are stable.
- NH, show hydrogen bonding while the other hydrides of this family do not form hydrogen bonds.
- Nitrogen forma nitride ion (N-) due to its small size and high electronegativity while except phosphorus (which can form phosphide ion (P) in some compounds) all other elements of this family do not form this type of anion.
- Due to absence of d-orbitals in its valence shell, its covalency is restricted to four, while other elements can extend their covalency upto 5 because of availability of d-orbitals.
- As nitrogen does not have d-orbitals so it cannot form dπ – pπ bonds. Though other elements of this family do not form pπ – pπ multiple bonds easily but they readily can form dπ – pπ multiple bonding.
- Hence, nitrogen cannot form R3N = O or R3N = CH2 but phosphorus and other can form R3P = O or R3P = CH2.
- Further more, due to presence of d-orbitals phosphorus and other elements except nitrogen can form P(C2H5)3, As(C6H5)3 which can acts as ligands in transition metal complexes. They can also form [PF6]–, [SbF6]– etc. but nitrogen cannot.
- Nitrogen is chemically inert under normal conditions because of very high dissociation energy required to break N ≡ N bond.
- Nitrogen is a typical non-metal while other members are either semi metals or metals.
- Nitrogen forma various oxides like N2O, NO, N2O3, NO2 and N2O5 which are monomeric while the oxides of phosphorus and arsenic exist as dimer (P4O6, P4O8, P4O10, As4O6, As4O8 etc.)