p-BLOCK ELEMENTS - NITROGEN FAMILY

GENERAL CHARACTERISTICS

The group 15 of the periodic table consists of nitrogen, phosphorous, arsenic, antimony and bismuth. These elements are known as pnicogens and their compounds as pnicomides.

ELECTRONIC CONFIGURATION

Element	At. No.	Electronic configuration	Valence shell
Nitrogen	7	[He] 2s2 2p3	2s2 2p3
Phosphorous	15	[Ne] 3s2, 3p3	3s2 3p3
Arsenic	33	[Ar] 3d10, 4s2 4p3	4s2 4p3
Antimony	51	[Kr] 4d10, 5s2 5p3	5s2 5p3
Bismuth	83	[Xe] 4f14, 5d10 6s2 6p3	6s2 6p3

METALLIC CHARACTER

N, P(non metals), As, Sb(metalloids), Bi(metal)

PHYSICAL STATE

Nitrogen is first element after hydrogen to be a diatomic gas in normal form. All other elements in the group are normally solids.

ATOMICITY

N2 is diatomic while others are tetra-atomic M4

MELTING AND BOILING POINTS

The melting point increases from nitrogen to arsenic. The boiling points increase regularly on moving down the group.

DENSITY

Density increases down the group.

ATOMIC RADII

Atomic radii increases with increase in atomic number.

COVALENT RADII

Covalent radii increases in a regular fashion down the group.

ALLOTROPY

All the elements (except bismuth) show allotropy.

Nitrogen - a-nitrogen, b-nitrogen

Phosphorus - white, Red, scarlet, violet, a-black, b-black

Arsenic - Grey, Yellow, Black

Antimony - Metallic, Yellow, Explosive

OXIDATION STATE

N	P	As	Sb	Bi
–3 to +5	–3, +3, +4, +5	+3, +5	+3, +5	+3, +5

Nitrogen has a wide range of oxidation states

Oxidation state	Example
+5	N2O5, HNO3,
+4	NO2, N2O4
+3	HNO2, , NF3
+2	NO
0	N2
–1	NH2OH, NH2F
–2	N2H4
–3	NH3, ,

NEGATIVE OXIDATION STATES

–3 oxidation state is exhibited by other elements also. Ca3P2, Na3As, Zn3Sb2

INERT PAIR EFFECT

Inert pair effect increases down the group and due to this effect, the stability of +3 oxidation state increases and stability of +5 oxidation state decreases on moving down the group.

IONISATION ENERGY

Ionisation energy of nitrogen is very high due to small atomic radius. The ionisation energy decreases down the group.

ELECTRONEGATIVITY

The electronegativity decreases from nitrogen to bismuth.

CATENATION

They exhibit the property of catenation but due to weak M–M bond to less extent than 14 group elements.

Bond C–C N–N P–P As–As

kJ/mol 353.3 163.7 201.6 147.4

REACTIVITY

Elemental nitrogen is highly unreactive largely because of its strong triple bond. (almost as inert as noble gases).

While phosphorus is extremely reactive and kept in water. It is inflammable and can be ignited at 45ºC. It shows green luminescence or glow in dark on account of its slow oxidation. This glow phenomenon is known as phosphorescence.

MULTIPLE BOND FORMATION

Only nitrogen has a tendency to form pp—pp multiple bonds. Others forms dp–pp multiple bonds easily.

COMPOUNDS OF GROUP 15 ELEMENTS

HYDRIDES

All the elements of this group form hydrides of the type MH3 which are covalent and pyramidal in shape.

Some properties follow the order which are

NH3 > PH3 > AsH3 > SbH3 > BiH3

Ammonia Phosphine Arsine Stabene Bismuthene

Ease of formation
Stability
Basic character
Solubility
Bond angle (NH3 107.5º ; PH3 92º, AsH3 91, SbH3 90º)
Strength of M – H bond
Dipole moment
Decomposition temperature

Some properties follow the order

NH3 < PH3 < AsH3 < SbH3 < BiH3

Reducing character
Covalent character
Poisonous character
Rate of combustion

Boiling points : BiH3 > SbH3 > NH3 > AsH3 > PH3

PREPARATION OF HYDRIDES

Some hydrides can be prepared as follows :

Ammonia

Any ammonium salt + metal oxide or hydroxide NH3

eg.

or (NH4)3PO4, NH4NO3, (NH4)2SO4,

(NH4)2SO3, (NH4)2S or (NH4)2 (C2O4)

Phosphine

Other hydrides

, M = As, Sb, Bi

HALIDES

All the elements of this group form trihalides of the type MX3 and except nitrogen all form pentahalides of the type MX5

MX3 M = N, P, As, Sb, Bi and X = F, Cl, Br or I

MX5 when X = F, M can be P, As, Sb and Bi
when X = Cl, M can be P, As and Sb

when X = Br, M can be P

NF3 is a colourless, odourless gas and the most stable of this series. It has low reactivity.

NCl3 is a yellow oily liquid that reacts with water to form ammonia and hypochlorous acid.

NI3 is shock sensitive and decomposes explosively when touched.

HYDROLYSIS

Ease of hydrolysis BiCl3 > SbCl3 > AsCl3 > PCl3 > NCl3
Trihalides except BiF3 are covalent in nature
Trihalides have pyramidal structure.

PENTAHALIDES

As nitrogen does not contain-vacant d-orbitals in the second shell and cannot expand its outer shell hence it does not form pentahalides.

The hybridisation in pentahalides is sp3d (trigonal bipyramidal)
Thermally less stable than trihalides
Act as Lewis acids
On complete hydrolysis they produce acids

OXIDES

All the elements of this group form oxides of the type M2O3 and M2O5. either by direct combination with O2 or indirectly.

Oxides of N

Oxides of P

Oxides of As

Oxides of Sb

Oxides of Bi

N2O (DINITROGEN OXIDE OR NITROUS OXIDE) known as laughing gas

Preparation :

Priestley’s method :
Bertholet’s (common method) :

Properties :

Colourless, fairly unreactive, pleasing odour, sweet taste, supports combustion. It is neutral.

Structure : Linear

Uses : Mixed with oxygen it is used as anaesthetic

NO (NITROGEN OXIDE OR NITRIC OXIDE)

Preparation :

(common method)
(commercial)
(Lab method)
(Ostwald’s process)

Properties : Colourless, paramagnetic, slightly toxic gas, blue in liquid state. It is combustible and supports combustion. It is neutral.

It is reducing as well as oxidising in nature.

Uses :

i) For manufacturing of nitric acid

ii) For detection of Oxygen

iii) For manufacturing of sulphuric acid as catalyst (Lead chamber process)

Structure :

NO2 (NITROGEN DIOXIDE)

Preparation :

(Common method)

Properties :
Highly toxic, paramagnetic, reddish brown gas with choking odour, acidic

Reactions :

(Hence it is mixed anhydride of HNO2 and HNO3)
It is combustible and supports the combustion of burning P, Mg or charcoal. Burning S or candle is extinguished.
It is oxidising and reducing in nature

Uses :

For Manufacturing of HNO3
As Catalyst in lead chamber process for Sulphuric acid

Structure :

N2O3 (DINITROGEN TRIOXIDE) NITROGEN SESQUIOXIDE

Preparation :

(common method)

Properties : It is blue solid, acidic

Hence it is anhydride of HNO2

Absorbed by sulphuric acid

Structure : Shape and structure is not definitely known

N2O5 (DINITROGEN PENTOXIDE)

Preparation :

(common method)

Properties : Colourless crystalline solid and sublimes

It is anhydride of nitric acid

Uses : It is powerful oxidising agent

Structure :

It’s ionic structure (by X-ray) is . It is also called nitronium nitrate.

P2O3 or P4O6 (PHOSPHORUS TRIOXIDE)

Preparation :

Properties : white solid like wax, garlic odour, highly poisonous.

Structure :

P2O5 or P4O10 (PHOSPHORUS PENTOXIDE) FLOWER OF PHOSPHOROUS

Preparation :

Properties : White crystalline solid smells like garlic, sublimes

Uses : Powerful dehydrating agent

Structure :

OXYACIDS OF N AND P

Both form a number of oxy acids which are as follows:

		Oxidation number	Basicity
Hyponitrous acid	H2N2O2	+1
Nitroxylic acid	H4N2O4	+2
Nitrous acid	HNO2	+3
Nitric acid	HNO3	+5
Peroxynitric acid	HNO4	+5
Hydronitrous acid	H2NO2	+2
Hypophosphorus acid	H3PO2	+1	1
Phosphorus acid	H3PO3	+3	2
Orthophosphoric acid	H3PO4	+5	3
Pyrophosphoric acid	H4P2O7	+5	4
Meta phosphoric acid	HPO3	+5	1
Hypophosphoric acid	H4P2O6	+4	4

NITROGEN

Discovered by Daniel Rutherford. Abundance in air is 78.15% by volume. It occurs in combined state as saltpetre (KNO3) and Chile Saltpetre (NaNO3). It is also known as Azote (without life)

PREPARATION

. It is violent reaction with flashes of light (volcano experiment)
Preparation of very pure N2 : By heating Sodium azide

MANUFACTURING

LINDE’S OR CLAUDE’S PROCESS

Atmospheric air is compressed and then released into a bigger area when liquid air is obtained (Joule Thomson effect) which is mainly mixture of N2 and O2. They are separated by fractional distillation.

PROPERTIES

It is colourless, odourless, tasteless, slightly lighter than air, slightly soluble in water, non poisonous gas.
It is incombustible and non supporter of combustion.
It combines with metals and non metals to form number of compounds.

USES

To decrease concentration of oxygen in air and make combustion less rapid. To create inert atmosphere and in the preparation of NH3, HNO3, CaCN2, etc.

AMMONIA (NH3)

PREPARATION

(lab method)

MANUFACTURING

Haber’s process :

Other catalysts employed are

(i) finely divided Os or U

(ii) Finely divided Ni deposited over pumice stone

(iii) Fe(OH)3 with traces of SiO2 and K2O

Cyanamide process :

Mixture of Calcium Cyanamide and graphite under the name of nitrolim is used as fertilizer.

Serpeck's process : As by product during hydrolysis of AlN

PROPERTIES

Colourless gas, characteristic pungent odour, brings tears into eyes, collected by downward displacement of air.
Extremely soluble in water due to H-bonding. It is a strong lewis base.
Ammonia is dried over any metal oxide but CaO is cheaper.
When passed through alkaline solution of Nessler's reagent a brown coloured complex known as Millon’s base is formed.

NITRIC ACID (HNO3)

also known as aqua fortis

PREPARATION

(lab method)

MANUFACTURING

Birkeland - Eyde process : Air is passed through an electric arc (3000ºC) when N2 combines with O2 to form NO. It is cooled and allowed to combine with O2 to form NO2. The latter is passed in water in presence of excess of air to give HNO3.

Ostwald’s Process : From ammonia

PHYSICAL PROPERTIES

Syrupy, colourless, pungent liquid usually available as 68% and 15.7 M. Aqueous solution is often yellow due to small concentrations of NO2

Fuming nitric acid (HNO3 + NO2)

CHEMICAL PROPERTIES

As an acid

It is a strong acid and in aqueous solution the ionisation is virtually complete.

⇌

Thus it reacts with basic oxides, hydroxides, carbonates etc.

As oxidising agent

(concentrated HNO3)

(dil. HNO3)

OXIDATION OF NON METALS -IC ACIDS ARE FORMED

(Sulphuric acid)

(Carbonic acid)

(Phosphoric acid)

(Iodic acid)

(Arsenic acid)

(Metastannic acid)

(Selenious acid)

(Tellurous acid)

OXIDATION OF COMPOUNDS

ACTION OF NITRIC ACID ON METALS

ARMSTRONG’S THEORY

The metal first displaces nascent hydrogen from acid which further reacts with acid to give secondary reactions.

Factors affecting the secondary reactions

Nature of the metal
Concentration of the acid
Temperature
Presence of impurities

ACTION OF NITRIC ACID ON ZINC UNDER DIFFERENT CONDITIONS

Cold and very dil. acid evolves ammonia which reacts with HNO3 forming ammonium nitrate

Cold and dil HNO3

Cold and moderately conc.

Cold and concentrated

ACTION OF NITRIC ACID ON COPPER UNDER DIFFERENT CONDITIONS

Cold and dil.

Cold and moderately concentrated

Cold and concentrated

Hot and conc.

Metals like Mg and Mn give hydrogen with dil. HNO3

PASSIVITY

Metals like, Fe, Cr, Ni, Al or Co become inactive or passive due to stable oxide layers.

Noble Metals like Pt, Pd, Os, Ir and Au do not react with nitric acid. They react with aqua regia (1 vol. Conc. HNO3 + 3 vol. Conc. HCl).

Similarly platinum forms

STRUCTURE OF NITRIC ACID

USES

In the manufacture of fertilizers ii) For purification of silver and gold iii) In the manufacture of explosives iv) oxidising reagent v) As nitrating reagent

NITROUS ACID (HNO2)

PREPARATION

PROPERTIES

It has slight bluish colour in solution may be due to anhydride N2O3. It is very unstable.

Decomposition

(auto oxidation)

Action of heat

Oxidising nature

(electron acceptor)

Reducing nature

(electron donor)

Reaction with ammonia

Formation of diazonium compounds

USES

In the manufacture of azo dyes.

STRUCTURE

It is a tautomeric mixture of the following forms

PHOSPHOROUS

Discovered by Brand

OCCURRENCE

It occurs in combination only as phosphates

Phosphorite Ca3(PO4)2
Chlorapatite CaCl2.3Ca3(PO4)2
Fluorapatite CaF2.3Ca3(PO4)2

In phosphoproteins of brain, bones, teeth, milk, egg, nervous tissues of animal and plants.

MANUFACTURING

By reduction of calcium phosphate with carbon in presence of SiO2 in an electric furnace

Purification : By melting under acidified solution of K2Cr2O7. The impurities are oxidised and redistilled.

PROPERTIES

Freshly prepared phosphorus is colourless. On standing acquires pale lemon colour due to formation of red phosphorus on the surface. It is therefore called yellow phosphorus. Due to its poisonous nature the jaw bones decay and disease is known as “Phossy jaw”

ALLOTROPIC FORMS OF PHOSPHORUS AND THEIR PREPARATION

Red phosphorous
By carefully heating yellow phosphorus in an inert atmosphere for about 8 days
Violet phosphorus
By crystallisation of white phosphorous from molten lead
Scarlet

By exposing the solution of red P in PBr3 to light or by boiling

By heating PBr3 with Hg at 513K

Black
By heating white P to 473K under 1000kg/sq. cm.
It is the most stable form, good conductor of electricity.

CHEMICAL PROPERTIES

With non metals

With metals

With compounds

USES

In matches, explosives, as rat poison and in fertilizers and alloys.

Match box
Side contains : Red P or P2S3 + Sand + Glue

On tip : Red P + Oxidising agent like KClO3 or KNO3 or Pb3O4 + glass powder or chalk for friction + glue

PHOSPHINE (PH3)

PREPARATION

Any phosphide + H2O PH3

Decomposition of H3PO3 :

Lab. method :

Pure PH3 :

PROPERTIES

Physical Properties : Colourless, highly poisonous, with rotten fish odour gas, slightly soluble in water
Basic nature :
Decomposition :
Combustibility :

Pure PH3 is not spontaneously inflammable. Ordinary PH3 is spontaneously inflammable due to the presence of P2H4

With metallic salts :
With chlorine :

USES

Holme’s signals : A mixture of CaC2 and Ca3P2 when treated with water, phosphine is liberated which catches fire and lights up acetylene. Burning gases serve the purpose of a signal. They are used in ships.
Smoke screen : Ca3P2 is used smoke screen. PH3 obtained from it catches fire to give the needed smoke.
Celphos : It is trade name of AlP, aluminium phosphide and used as fumigant. In presence of moisture it gives PH3 which kills insects and pests
Rat poison : Zinc phosphide Zn3P2 is a rat poison, which gives PH3

ORTHOPHOSPHORIC ACID (H3PO4)

PREPARATION

PROPERTIES

Physical Properties - Colourless syrupy liquid
Action of heat
It is tribasic and ionises in three steps

(Readily)

(Weakly)

(very weak ionisation)

USES

For preparation of HBr, HI in laboratory
For preparing metaphosphoric acid
Stabiliser for H2O2

ORTHOPHOSPHORUS ACID (H3PO3)

PREPARATION

PROPERTIES

Physical Properties - It crystallises as deliquescent white solid
Acidic nature : ⇌ ⇌
Decomposition : . This reaction is disproportionation
Reducing nature :

(colour of I2 discharged)

USES

As reducing agent

FERTILIZERS

Fertilizers are the chemical substances which are added to soil in order to make up the deficiency of nutrients required by plants. Nutrients are classified as-

Primary nutrients : which are consumed in large quantities eg. Nitrogen, Phosphorus and Potassium
Secondary nutrients : Calcium and Magnesium
Micro nutrients : which are required in minute quantities eg. Copper, Zinc, Manganese, Boron, Molybdenum, chlorine and Iron