Chemistry ATOMIC & PHYSICAL PROPERTIES, FORMATION OF HYDRIDE AND HALIDES

Atomic and Physical Properties :

The elements are : `N`, `P` [Non metal], `As` [Metalloid], `Sb`, `Bi` [Metal]

The General electronic configuration is [noble gas] `ns^2 np^3`

`(i) text(Atomic and Ionic radii)` : Covalent radius : `N < P < As < Sb < Bi`

`(ii) text(Ionization enthalpies :)` `N > P> As > Sb > Bi` ( `IE_1` values)

`(iii) text(Electronegativity :)` `N > P > As > Sb = Bi`

`(iv) text(Metallic Character :)` `(N < P)/text(Non metal) (< As)/text(Metalloid) (< Sb < Bi)/text(Metals)`

`(v) text(Catenation :)`

`ast` The group `15` elements also show catenation property but to much smaller extent than carbon. For example hydrazine `(H_2N NH_2)` has two `N` atoms bonded together. `HN_3` has three `N` atoms.

`HN_3` `quad quad` `H-overset(..)(N) = overset(+)(N)=overset(..)(N):^(-)`

`ast` Among group `15` elements `P` has the maximum tendency for catenation forming cyclic as well as open chain compounds consisting of many phosphorous atoms.

`P_2H_4` has two `P` atoms bonded together the lesser tendency of elements of group `15` to show catenation in compression to carbon is their low dissociation enthalpies.

`C - C quad 353.3 kJ //text(mole)`
`N - N quad 16.8 kJ // text(mole)`
`P - P quad 201.6 kJ // text(mole)`
`As - As quad 147.4 kJ // text(mole)`

`(vi)` `text(Valency and Oxidation Number :)`

(a) Gen. configuration : `ns^2 np^3`

Valency = 3

O.S. = `- 3, + 3,+ 5`
`P` show O.S. = `-3, + 3`

(b) `P` has two sleeping valency.

(c) `text(Sleeping Valency :)` These electron of valency shell which does not take part in bonding.

(d) `P` in excited state show `+ 5` O.S.

So Hybridisation `= sp^3d`

Shape = Trigonal bipyramidal.

(e) `P`, `As`, `Sb` show `3` & `5` both O.S.

`N` only `3`, absence of `d`-orbital

`Bi` only 3, because of inert pair effect

`(vii)` `text(Reactivity :)`

(a) `downarrow` Decreases [E.N. Decrease]

(b) Least reactive in `V` group is `N` {due to triple bond formation of Bond Energy (uparrow)}

(c) Max. Reactive in `V` group is `P`.

(d) Order `P > As > Sb > Bi > N`

`(viii)` `text(Allotropic Forms :)` Except `N` and `Bi` all other elements of this group show allotropy.

Phosphorous : White, Black and Red

Arsenic : Yellow or Grey

Antimony : Yellow or Silvery grey.

`ast` `text(Arsenic) (As) :` It is the most poisonous element of `V^(th)` group.

Abnormal Behaviour of Nitrogen :

(a) Nitrogen is a gas, while other elements are solids.

(b) Nitrogen molecule is diatomic `(N_2)` while molecules of `P`, `As` and `Sb` are tetra atomic `(P_4,As_4, Sb_4)` and that of `Bi` is mono atomic.

(c) Halides of nitrogen except `NF_3` are highly explosive.

(d) `N_2O_3` and `N_2O_5` are monomeric while trioxides and pentoxides of `P`, `As` and `Sb` are dimeric.

(e) It is chemically inert due to the presence of triple bond other elements are highly reactive due to presence of single bond in their molecule.

(f) `N equiv N`, `C = O`, `(C equiv N)^(-)` are isoelectronic species but `N equiv N` is less reactive due to nonpolar nature and high ionisation energy.

(g) `N` does not form sulphides.

(h) Nitrogen occurs in free state but others are not.

Compounds of V-A Group :

`text(FORMATION OF HYDRIDES)`

(a) Hydrides formed have `YH_3` formula- `(NH_3, PH_3 , AsH_3, SbH_3, BiH_3)`

(b) Except `NH_3`, all Hydrides are poisonous.

(c) `NH_3` neutralises protic acids as well as aprotic acids (Lewis Acid) so ammonia is strong base.

(d) `undersettext(Phosphene)(PH_3) + HI -> undersettext(Phosphonium Iodide)(PH_4I)`

Phosphene is a weak base as compared to `NH_3` and rest all have amphoteric nature.

(e) `NH_3` will have high boiling point due to `H`-bond.

(f) Tendency of `H`-bonding and B.P.

`NH_3 > PH_3 < AsH_3 < SbH_3 < BiH_3` .

(g) `NH_3` cannot acts as a reducing agent and `BiH_3` is strongest reducing agent.

(h) Stability decreases from `NH_3` to `BiH_3`

Size increases and so bond strength decreases.

(i) Oxidation state :

Hydrazine `NH_2 - NH_2` or `N_2H_4 => - 2`

Hydrazoic Acid `N_3H => - 1/3`

`NH_2 - OH => - 1`

(j) Hydrazine is used as propellant for rocket fuels. It is undergoes combustion releasing large amount of energy.

(k) `H_2O_2` also a better propellent than `N_2H_4`.

`H_2O_2` provides nascent `O` which is more reactive than `O_2`.

(l) `N_3^-` is called Azide Ion ` ->` Has `4` lone pair

Eg. `Ba+2N_3^(-) ->` Barium Azide `[Ba(N_3)_2]`.

Formation of Halides :

(i)`YX_3` (ii) `YX_5`

(i) `text(Tri Halides :)` All possible trihalides of all these elements are known except `NCl_3, NBr_3,` and `NI_3`

Because :

(a) Low polarity of the `N-X` bond.

(b) Weakness of `N-X` bond due to large size difference.

(c) `NCl_3 + 3H_2O -> NH_3 + 3HOCl`

`PCl_3 + 3H_2O -> H_3PO_3 + 3HCl`

`SbCl_3 + 3H_2O -> SbOCl + 2HCl` (Stibynl Chloride)

`BiCl_3 + H_2O -> BiOCl + 2HCl` (Bismithyl Chloride)

When an aq. solution of `BiCl_3` is prepared, after some time a turbidity appears which is milky in appearance and finally a white ppt. is formed due to formation of `BiOCl`.

(d) Lewis Base Order :

`NF_3 < NCl_3 < NBr_3 < NI_3`.

(ii) `text(Penta Halides :)`

(a) Except `N` and `Bi` all forms pentahalides, `N` does not form due to absence of `d`-orbital `Bi` does not form due to inert pair effect.

(b) `PCl_5` acts as an effective chlorinating Agent so it decomposes into `PCl_5 -> PCl_3 + Cl_2`