The elements nitrogen (N), phosphorous (P), arsenic (Ar), antimony (Sb) and bismuth
(Bi) constitute group 15 or VA of periodic table. Nitrogen is very important and well known
element of this group. It constitutes nearly 78.1percent by volume and 75.5 percent by weight of the
air is essential constituent of fertilizers, explosives and food stuffs.
After the name of the first element these elements are collectively known as nitrogen family. These
elements are also known as pnictogens and their compounds pnictides which contain X3- species.
Nitrogen and phosphorus are non metals arsenic and antimony are metalloids and bismuth is a metal.
Physical Properties of Nitrogen
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The physical properties of group 15 elements are given below.
1. Physical state - There is a gradual change in physical states of these elements are observed.
Nitrogen is a gas, phosphorus is solid and at low temperature it can be vaporized. The other
three elements are solids.
2. Metallic and non metallic character - Metallic character varies depending on the change in
atomic number. Nitrogen and phosphorus are non metals whereas arsenic, antimony and
bismuth are metals.
3. Allotropy - All elements exhibit allotropy except nitrogen. Phosphorus exists as white, red,
scarlet and black phosphorus, arsenic exists in three forms grey, yellow and black, arsenic
exists as yellow, black and explosive antimony.
4. Melting and boiling points - On moving down the group the melting and boiling points
increases with increase in atomic number.
5. Density - Density also increases on moving down the group with increase in atomic number.
6. Atomic volume, atomic radius and ionic radius - All these property increases with increase in
atomic number of the elements of group 15.
7. Electronegativity - it decreases on moving down the group indicating a gradual change from
non metallic to metallic character.
8. Ionization energies - It decreases regularly on moving down the group due to increase in size
of the atom and decreasing shielding effect of electrons from the nucleus.
9. Oxidation state - it exhibit both positive and negative oxidation state. The common oxidation
state is +3. nitrogen shows +1, +2, +4 and +5 and phosphorous shows +4 oxidation state also.
10. Catenation - it is shown by all the elements of this group. as is apparent from bond energies the
tendency for catenation decreases on moving down the group from nitrogen to bismuth.
Chemical Properties of Nitrogen
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The chemical properties of group 15 elements are given below.
Formation of hydride
M + H2 → MH3
All elements form MH3 type hydride. The thermal stability of hydride of this group decreases on
moving down the group. This is due to the increase in atomic size. The basic nature also decreases
on moving down the group because of the increase in size of the central metal atom. The melting
point and boiling point goes on increasing as we move down the group due to increase in molecular
size. Except ammonia (NH3) all other hydride of other elements do not exhibit hydrogen bonding. All
hydride are pyramidal in shape. On moving down the group the bond angles decrease due to
decrease in bond-pair-bond-pair repulsion.
Formation of oxides
M + O2 → MO2
M + O2 → M2O3
All the elements of this group form three oxides except nitrogen which forms five oxides. Nitrogen
forms N2O, NO, N2O3, NO2 and N2O5. Phosphorus also forms an extensive series of sulphides and
the most stable is tetra phosphorus trisulfide P4S3. The main use of this compound is it is used in
strike anywhere matches. Apart for this other elements As, Sb and Bi form oxides of general formula
M2O3. The oxides of nitrogen and phosphorus are acidic and arsenic and antimony are amphoteric
and bismuth is basic in nature.
Formation of oxyacids
In nitrogen several oxyacids are unstable in pure state and are known only in aqueous solution or as
their salts. only two are well known. One is Nitrous acid (HNO 3) and the other is nitric acid (HNO3).
Nitrous acid is a weak acid in aqueous solution and sodium nitrate is is mildly toxic to human beings.
Nitric acid is prepared by Ostwald process. In combination with concentrated HCl aqua-regia is
formed. Apart for these two hypo nitrous acid and peroxonitric acid are also called oxyacids of
nitrogen. Important oxyacids of phosphorus are listed below.
1. Orthophosphoric acid - H3PO4
2. Pyrophosphoric acid - H4P2O7
3. Metaphosphoric acid - HPO3
4. Phosphonic acid - H3PO3
5. Hypophosphorys acid - H3PO2
6. Hypophosphoric acid - H4P2O6
Formation of halides
M + X (halogen) → MX3
All the elements of this group form halides of the type MX3. The most stable halides of nitrogen is NF3.
Except NF3 and PF3 trihalides are hydrolyzed by water and the ease of hydrolysis decreases down
the group. NCl3 is easily hydrolyzed and SbCl3 and BiCl3 are partly hydrolyzed. P and Sb form stable
pentahalides but nitrogen do not form pentahalides due to absence of d-orbitals in valence shell. Bi do
not form pentahalides due to inert pair effect. PCl5 is used as a chlorinating agent.
Hydrazine
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Hydrazine is a colorless fuming liquid. The odor is like ammonia. It is prepared by the oxidation of
ammonia with alkaline sodium hypochlorite in the presence of gelatin.
2NH3(aq) + NaClO(aq) ⇌ N2H4(aq) + NaCl(aq) + H2O(l)
Hydrazine is a strong reducing agent as reflected in the reduction potential. Hydrazine reducing ability
is exploited in its use in waste water treatment for chemical plants. A related use is the treatment of
water boilers in large electric generating plants.
Hydrazoic acid
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In hydrazoic acid 3 nitrogen atoms are linked together. To synthesize the acid it is therefore
reasonable to start with compounds in which 2 nitrogen atoms are already bound together such as
dinitrogen oxide or hydrazine.
Free hydrazoic acid can be obtained in high yield from the sodium salt by distillation with dilute
sulfuric acid followed by dehydration of the distillate with calcium chloride. Hydrazine can be
converted to hydrazoic acid by reaction with nitrous acid in either at 0 oC in the presence of sodium
methoxide which forms the sodium salt.
HNO2 + H4N2 → HN3 + 2H2O
Hydroxylamine
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Hydroxylamine is a key intermediate in nitrogen fixation. Hydroxylamine can be prepared by the
reduction of hydroxylamine hydrochloride by sodium but-oxide in solution or from the oxidation of
nitrogen monoxide or the hydrolysis of nitroparaffins.
It is used to prepare oximes, an important functional group. It is also an intermediate in biological
nitrification. Hydroxyamine is used as a nucleophile in aromatic substitution reactions as a reducing
agents and for the conversion of aldehyde to nitriles.
Nitric Oxide
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It is a colorless gas produced in the laboratory when copper metal is treated with dilute nitric acid.
3Cu(s) + 2NO3-(aq) + 8H+(aq) → 3Cu2+(aq) + 2No(g) + 4H2O(l)
Nitric oxide is also important in many biological processes where it helps transmit messages between
nerve cells and kills harmful bacteria. It also helps to protect the heart from insufficient oxygen levels
by dilating blood vessels.
Nitrous Oxide
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Nitrous oxide (N2O) is a colorless, sweet smelling gas obtained when molten ammonium nitrate is
heated gently at about 270oC. strong heating of this compound can produce explosion.
NH4NO3(l) →Heat N2O(g) + 2H2O(g)
Known as laughing gas because small dose are mildly intoxicating, nitrous oxide is used as a dental
anesthetic and as a propellent for dispensing whipped cream.
Uses of Nitrogen
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Nitrogen is used for a large number of purposes. These include inerting, process, purging and
pressurizing. One main use of nitrogen is inerting. Inert atmospheres are often required in processes
such as polymerization, catalyst preparation and regeneration and in plant such as centrifuges and
storage tanks.
In particular it may be used to dilute the concentration of a reactant such as oxygen in an oxidation
process. In high pressure processes the use of nitrogen permits the use of such pressures while
limiting the partial pressure of oxygen.
Nitrogen Family Reactivity
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Nitrogen is chemically the least reactive of all elements, and enters into chemical reactions only at
very high temperatures. Nitrogen is considered as an inert element because nitrogen gas normally
does not interact with other substances. Individual atoms of nitrogen are highly reactive.
Nitrogen is a gas at room temperature. A nitrogen molecule N2 consists of two atoms bonded by a
triple covalent bond. Phosphorous on the other hand is very reactive. In general the reactivity
increases on going down the group. The trend in reactivity is shown below.
Nitrogen Family Characteristics
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1. Atomic radii - Atomic radii of these elements increases in moving down the group.
2. Ionization energy - The ionization energy decreases regularly in moving down from nitrogen to
bismuth.
3. Electronegativity - The electronegativity value decreases on moving down the group from
nitrogen to bismuth.
4. Melting point and boiling point - Both the properties increases from nitrogen to arsenic due to
increase in molecular size.
5. Metallic character - On moving down the group metallic group increases.
6. Density - This property increases down the group.
Nitrogen Family Uses
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1. Nitrogen is used in fertilizer production and more multiple application of nitrogen fertilizer to
obtain more efficient use of nitrogen fertilizer.
2. Phosphorus are used for corrosion control in water supply and industrial cooling water
systems. Certain organic compounds are used in insecticides.
3. The historical use of arsenic were pharmaceutical and medicinal. Arsenic was also commonly
used in pigments, poisons and in the manufacturing of glass. A major modern use for arsenic
was as pesticides in agriculture.
4. Antimony is used in the metallurgy industry, especially in alloys. When it is added to other
metals such as lead, it hardens them. It is employed for the manufacture of battery plates and in
type metal as well as solders ammunition and electric cable coverings.
5. The principle uses for bismuth are in low melting alloys in metallurgical additives for aluminum,
carbon steel and malleable iron in pearlescent cosmetic pigments in medicine and in a variety of
other smaller specialized applications. The largest single use of bismuth continues to be in the
pharmaceutical field.