2. GROUP 15 ELEMENTS
Element Symbol Atomic No. Metal or
Non-metal
Nitrogen N 7 Non-metal
Phosphorus P 15 Non-metal
Arsenic As 33 Semi-metal
Antimony Sb 51 Semi-metal
Bismuth Bi 83 Metal
2
3. Atomic & Physical Properties
■ Ground state valence shell electronic
configuration ns2np3.
■ The covalent radius increases as we
descend the group.
■ Electro negativities decrease down the
group, except N the rest elements have low
& almost similar electro negativities.
■ Nitrogen is gas, P, As,Sb & Bi are solids
under normal conditions.
3
4. OXIDATION STATES
■ Common oxidation states for P & As are –
3, +3 & +5.
■ For Sb & Bi , oxidation states are +3 & +5.
■ The stability of the highest oxidation state
(+5) decreases down the group due to inert
pair effect.
■ The +5 state in Bi is less stable than in Sb.
■ The only well characterized Bi(V)
compound is BiF5
4
5. Trends in Chemical Reactivity
■ There is a decrease in covalent character in
the sequence P > As > Sb > Bi.
■ P displays essentially covalent character
although it can accept 3 electrons to form
phosphides.
■ Sb & Bi form M3+ cations due to decrease
in ionization enthalpy.
■ The tendency to form double and triple
bonds relative to single bonds diminishes
markedly.
5
6. •P, As & Sb form tetrahedral E4 molecules in
their elemental state containing E-E single
bonds.
•P shows a distinct tendency for catenation
forming both cyclic and open chain compounds
containing P atoms.
•The heavier members can form penta- and
hexa-coordinated derivatives such as PCl5, AsF5
& PF6
-.
6
7. Hydrides of Group 15 Elements
■ All elements of group 15 form gaseous
hydrides of the type MH3
■ The stability of the hydrides decreases
sharply down the group.
■ Except NH3, all the hydrides are strong
reducing agents.
■ Except NH3, all the hydrides are highly
poisonous.
7
8. •NH3 is associated via H-bonds, while other
hydrides are not associated in the liquid state
and are rather insoluble in water.
•PH3 is a much weaker base than NH3; AsH3,
SbH3 & BiH3 do not show any basic properties.
•These hydrides have a pyramidal structure.
8
9. Halides of Group 15 Elements
■ They form two type of halides, MX3 &
MX5
■ Bonding in the trihalo compounds is
predominantly covalent except in BiF3.
■ PCl3 is a colourless liquid, it fumes in
moist air because of its reaction with water
producing HCl.
PCl3 + H2O → H3PO3 + 3HCl
9
10. •PCl3 reacts with O2 to form phosphoryl
chloride, P(O)Cl3.
•Tri halides have a pyramidal structure in the
gaseous state.
•E.g. PF3
10
11. •PF5 is molecular in both the gaseous & solid
states and has a trigonal bipyramidal structure.
11
12. •PCl5 is molecular in the gas and liquid phases
but in the solid state exists as [PCl4]+[PCl6]-
containing tetra and hexa-coordinated
phosphorus species.
•PCl5 is made by the reaction of PCl3 with Cl2 in
CCl4:- PCl3 + Cl2 → PCl5
•PCl5 fumes in air, it reacts with water to give
initially POCl3; if water is excess, the product is
H3PO4. PCl5 + H2O → POCl3 + 2HCl
POCl3 + 3H2O → H3PO4 + 3HCl
12
13. Oxides Of Group 15 Elements
■ P, As,Sb & Bi form two types of oxides:-
E2O3 & E2O5.
■ The reluctance of P, As,Sb & Bi to enter
into pπ- pπ multiple bonding leads to cage
structures for their oxides and they exist as
the dimers, E4O6 and E4O10.
■ Bi(V) oxide is unstable.
13
14. Structure of P4O6 & P4O10
•P atoms are at the corners of the tetrahedron as in white P.
Six oxygen atoms are along the edges forming P-O-P single
bonds
14
15. •Both P4O6 & P4O10 are acidic oxides which
dissolve in water to give Phosphonic acid
(Phosphorous acid) and Phosphoric acid
(orthophosphoric acid) respectively.
P4O6 + 6H2O → 4 H3PO3
P4O10 + 6H2O → 4 H3PO4
•P4O10 is used as a dehydrating agent because of
its great affinity for water. It can dehydrate HNO3
and H2SO4 to yield N2O5 and SO3 respectively.
15
16. •The basic nature of the oxides increases with
increasing atomic number.
•P2O3 & As2O3 are acidic; Sb2O3 is amphoteric
and Bi2O3 is basic.
•Bi2O3 dissolves in acids to give salts:
Bi2O3 + 6 HNO3 → 2Bi(NO3) + 3 H2O
16
17. OXOACIDS OF PHOSPHORUS
■ Oxoacids are based on tetrahedral four
coordinated P containing at least one P = O
unit and one P – OH group.
■ Examples: - Phosphinic acid, phosphonic acid
& orthophosphoric acid.
■ Two or more P(O)(OH)3 units can join to give
Condensed Phosphoric acids having P-O-P
links. They can have cyclic or linear chain
structures.E.g. Pyrophosphoric acid,H2P2O7
Cyclotrimetaphosphoric acid (HPO3)3 .
17
19. PHOSPHINIC ACID
■ Also called
hypophosphorous acid,
H3PO2.
■ It has one P(OH) group
and two hydrogen
directly attached to
phosphorus.
■ It has only one ionisable
H & hence behaves as a
monoprotic acid
19
20. PHOSPHONIC ACID
■Also called phosphorous acid, H3PO3.
■It is a diprotic because it contains two
ionisable hydrogen.
■It forms two series of salts, NaH2PO3 &
Na2HPO3 .
20
21. ORTHPHOSPHORIC ACID
■ H3PO4, also called
phosphoric acid.
■ It is a triprotic acid.
■ It forms three series
of salts,e.g. NaH2PO4,
Na2HPO4, & Na3PO4.
■ It is used for the
manufacture of
Phosphatic fertilizers.
21
22. PHOSPHORUS
■ It occurs as phosphate rock which consists of
the minerals hydroxyapatite and florapatite.
■ It is present in bones and in living cells.
■ Elemental P is obtained by the reduction of
calcined phosphate rock with coke and
sand.The P vapour thus obtained is condensed
to a solid and stored under water to protect it
from reaction with air.
■ 2Ca3(PO4)2 + 6SiO2 +10 C → P4 + 6CaSiO3 +10CO
22
24. White Phosphorus
■ It is formed by condensation from the
gaseous or liquid states.
■ It is a waxy solid, insoluble in water but
highly soluble in CS2 & benzene.
■ It is highly reactive and spontaneously
ignites in air. Hence it is stored under water.
■ It glows in dark and this property gives the
element its name PHOSPHORUS (Greek for
light bringing)
24
25. •White P consists of discrete P4 molecules in
which the 4 P atoms are at the corners of a
tetrahedron and each P atom is covalently linked to
the other three P atoms.
•It is also known as
yellow phosphorus.
•It is highly toxic.
25
26. Red Phosphorus
■ When white P is heated at 570 K in an inert
atmosphere for several days, it gets
converted into red phosphorus.
■ It has higher melting point and greater
density than white P.
■ It is much less reactive than white P.
■ It is essentially non-toxic.
26
28. Black Phosphorus
■ It is thermodynamically most stable form
of P.
■ It is obtained by heating white phosphorus
at 470 K under high pressure. A series of
phases of black phosphorus are formed.
■ One of these phases consists of an extended
layer structure in which each P is bound to
three neighbours by single bonds.
28
29. Uses of phosphorus & its compounds
■ Used in the manufacture of (i) phosphatic
fertilizers, (ii) food-grade phosphates, (iii)
detergent phosphates &
(iv) pharmaceuticals.
■ Elemental phosphorus is used in water
industry and is the starting material for the
manufacture of organo-phosphorus
compounds used as pesticide
29
