REACTIONS OF NON-METALS
Non-metals are found on the right hand side of the Periodic Table. While all metals are solids with the
exception of mercury that is a liquid, non-metals occur as solids and gases with the exception of
bromine that is a liquid. The inert gases do not react with other elements. The three principal
constituent gases of the atmosphere are diatomic molecules: H2, N2 and O2. This study of nonmetals will be restricted to carbon, phosphorus, sulphur, and three of the halogens, chlorine, bromine
and iodine.
CARBON, SULPHUR AND PHOSPHORUS
CARBON
Occurs in charcoal,
graphite and diamond.
Available in the
laboratory as a fine
powder or as a carbon
block.
SULPHUR
Available in the form of
yellow powder called
flowers of sulphur or as
roll sulphur.
Reactions with oxygen
in air
Carbon glows red when
heated but does not
ignite:
C + O2  CO2.
Reaction is exothermic.
Sulphur ignites with
difficulty when heated
and burns with a blue
flame giving off choking
fumes of sulphur(IV)
oxide:
S + O2  SO2.
Reaction is exothermic.
Reactions with pure
oxygen
Carbon ignites on
heating and burns with a
yellow flame:
C + O2  CO2.
Sulphur ignites more
readily when heated and
burns more energetically
with a blue flame giving
off choking fumes of
sulphur(IV) oxide:
S + O2  SO2.
Dissolution of oxides
Carbon dioxide
dissolves in water to
form a weak acid called
carbonic acid (soda
water):
CO2 + H2O  H2CO3
Effect of solutions on
litmus.
Turns red.
Sulphur dioxide
(sulphur(IV) oxide)
dissolves in water to
form a weak acid called
sulphurous acid:
SO2 + H2O  H2SO3
Sulphurous acid causes
“acid rain”.
Turns red.
Physical properties
PHOSPHORUS
Red phosphorus occurs
as a fine powder. White
phosphorus occurs in
sticks that are stored
under water because
white phosphorus is very
unstable.
Phosphorus ignites
spontaneously without
heating and burns with a
bright yellow flame giving
off large quantities of
white phosphorus(V)
oxide vapours:
4P + 5O2  2P2O5.
Reaction is exothermic.
Phosphorus ignites
spontaneously and burns
more energetically with a
bright yellow flame giving
off large quantities of
white phosphorus(V)
oxide vapours:
4P + 5O2  2P2O5.
Phosphorus pentoxide
(phosphorus(V) oxide)
dissolves in water to
form a weak acid called
ortho-phosphoric acid:
P2O5 + 3H2O  2H3PO4.
Turns red.
Order of increasing reactivity: C, S, P
HALOGENS (CHLORINE, BROMINE AND IODINE)
Halogens occur in nature as diatomic molecules: F2, Cl2, Br2 and I2. Fluorine is so reactive that it is
not used in school laboratories. Cl2 is a yellow-green gas, Br2 a reddish-brown liquid and I2 a
purplish-black crystalline solid.
TEST FOR HALOGENS
Halogens can be identified by the colour of a solution of the halogen in carbon disulphide, carbon tetrachloride
or chloroform:
Chlorine - colourless
Bromine - yellow-brown
Iodine – purple.
CS2 sinks to the bottom of the test tube because it is denser than water. (Molar mass of CS 2 = 76 g.mol-1
compared with the molar mass of H2O = 18 g.mol-1.)
REACTION WITH METALS
The reactions between iodine and the metals sodium and zinc will be studied.
Sodium reacts spontaneously with iodine burning with a yellow flame and giving off purple iodine vapours while
yellow sparks shoot out in all directions: 2Na + I2  2NaI. The reaction is exothermic.
Zinc reacts with iodine after a drop of water has been added as a catalyst: Zn + I 2  ZnI2. The reaction is
exothermic.
Sodium is more reactive than zinc.
The products formed are called halides. For example, the halogen, iodine, becomes the halide, iodide.
DISPLACEMENT OF HALIDES BY HALOGENS
Since chlorine and bromine are very toxic, chlorine water and bromine water are used for reactions in the
laboratory.
A halogen can displace any other halogen that appears lower down in the reactivity series from a halide
solution.
Reactivity series for halogens:
F2
Cl2
Br2
I2
KCl (aq)
KBr (aq)
KI (aq)
Cl2
x


Br2
x
x

Cl2 + 2KBr  2KCl + Br2
Cl2 + 2KI  2KCl + I2
Br2 + 2KI  2KBr + I2