Group 15 elements

p block, group 15, class 12 chemistry, class 11 chemistry, nitrogen family

1. Group 15 elements : The NITROGEN Family Puneeta Malhotra

2. Group 15 Group 15 or the Nitrogen family has Nitrogen (N) , Phosphorous (P) , Arsenic (As) ,Antimony( Sb ) , Bismith (Bi) . Nitrogen comprises 78% by volume of the atmosphere

3. Electronic Configuration General electronic configuration ns 2 np 3 Oxidation state -3, +3 and +5 Stability of +5 OS decreases as we move down the group due to inert pair effect.

4. What is Inert Pair Effect ? Reluctance of ns 2 electrons to take part in bonding due to the poor shielding effect of intervening d and f orbitals on moving down the group is known as Inert Pair Effect .

5. ATOMIC SIZE

6. Atomic Radii Atomic Radii (pm)   N 70 P 110 As 121 Sb 141 Bi 148 On moving down the group atomic radius is expected to increase. Across the period atomic radii decrease As to Bi only a small increase in radius is observed due to ineffective shielding of filled d and/or f orbitals

7. Ionization Enthalpy The ionization enthalpy values decreases down the group due to increase in size. IE1<IE2<IE3 Group 15 elements have higher IE than group 14 and group16 due to stable half filled configuration

8. Electronegativity Down the group, electro negativity decreases N is most electronegative element of the group N forms Hydrogen bonds

9. Physical Properties All the elements of this group are polyatomic . Except nitrogen, all the elements show allotropy and catenation Exception: N is diatomic as N-N is weak due to interelectronic repulsion of lone pair Metallic character increases down the group due to decrease in ionisation enthalpy and increase in atomic size. N, P are non metals, As Sb metalloids and Bi metal

10. Oxidation State And Trends In Chemical Reactivity Show OS -3, +3 and +5 tendency to exhibit –3 oxidation state decreases down the group due to increase in size and metallic character. The stability of +5 oxidation state decreases and that of +3 state increases (due to inert pair effect) down the group. Bi only forms BiF5 Nitrogen undergoes dispropornation 3HNO2 → HNO3 + H2O + 2NO

11. Due to small size, high elecrtonegativity, high IE and non availability of d orbitals N2 is unreactive (inert) due to strong pπ – pπ Other elements of group donot form strong pπ – pπ as their atomic orbitals are large and diffuse so they cannot have effective overlapping nitrogen cannot form dπ – pπ and dπ – dπ bond and maximum covalency of 4 : due to non availability of d orbitals Nitrogen cannot form R3P = O type compounds, or R3P = CH2 (R = alkyl group). Phosphorus, NCl5 not formed Anomalous properties of nitrogen

12. Reactivity Towards Hydrogen hydrides have formula EH3 Bond dissociation enthalpy decreases down the group. Small size N overlaps better with H and overlap becomes less effective with increase in size of atom. The stability of hydrides decreases from NH3 to BiH3 due to decrease in bond dissociation enthalpy the reducing character of the hydrides increases down the group due to decrease in bond dissociation enthalpy. BiH3 is a strong reducing agent

13. All hydrides are Lewis bases due to presence of lone pair of electrons Basicity decreases in the order NH3 > PH3 > AsH3 > SbH3 > BiH3 as The electron density on central atom decreases down the group due to increase in size of central atom Bond angle decreases down the group Since nitrogen atom is highly electronegative. So in NH3 there is high electron density around the N atom which causes greater repulsions between the electron pairs around the N atom resulting in maximum bond angle. Since electronegativity decreases down the group, the electron density also decreases and consequently the repulsive interactions between the electron pairs also decrease thereby decreasing the bond angle H-M-H. Ammonia has higher bp than PH3 and AsH3 though bp increase down the group due to strong hydrogen bonding in NH3

14. Reactivity Towards Oxygen Form oxides with formula E2O3 and E2O5 The oxide in the higher oxidation state of the element is more acidic than that of lower oxidation state acidic character decreases down the group because metallic character increases NO2 dimerise as NO2 contains odd number of valence electrons. On dimerisation , it is converted to stable N2O4 molecule with even number of electrons and is stable. covalence of nitrogen in N2O5 is 4

15. Reactivity Towards Halogens Form Halides with formula EX3 and EX5. Nitrogen does not form pentahalide due to non-availability of the d orbitals in its valence shell. Pentahalides are more covalent than trihalides . Higher the positive oxidation state of central atom, more will be its polarising power which, in turn, increases the covalent character of bond formed between the central atom and the other atom. All the trihalides of these elements except those of nitrogen are stable. In case of nitrogen, only NF3 is known to be stable. Trihalides except BiF3 are predominantly covalent in nature. Bi is metallic in nature

16. Oxoacids of Phosphorous

17. P-H bond is responsible for reducing character H3PO2 good reducing agent due to 2 P-H bonds Basicity (or n factor) depends no. of P-OH bonds H3PO2 is monobasic, H3PO3 is dibasic and H3PO4 is tribasic Oxoacids in +3 OS disproportionate 4 H3PO3 3 H3PO4 + PH3

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