Page 17 - Chemistry ICSE Class IX
P. 17
The Language of Chemistry 5
Thus, Valency of sodium in sodium chloride = 1+
and Valency of chlorine in sodium chloride = 1–
Elements having 5, 6 or 7 electrons in their valence shell,
their valency = (8 – valence electron)
Elements having 1, 2, 3, 4 electrons in their valence shell,
their valency = no. of valence electrons.
What is valency of an element
Atoms combine to form molecules. The combining tendency of atoms is
de ned in terms of their valencies.
The valency of an element may be de ned as follows:
The number of hydrogen atoms or chlorine atoms or double the
number of oxygen atoms which combine with one atom of the element is
called its valency.
For example:
In HCl (hydrogen chloride), one atom of chlorine (Cl) is combined
with one atom of hydrogen (H). So,
Valency of chlorine in HCl = 1
In ammonia molecule (NH ), one atom of nitrogen combines with
3
three atoms of hydrogen. So,
Valency of nitrogen (N) in ammonia (NH ) = 3
3
The valency of a metal M in its oxide M O can be obtained as follows:
2
3
No. of oxygen atoms combining with two atoms of M = 3
3
So, No. of oxygen atoms combining with one atom of M =
As per de nition, 2
Valency of metal = Double the number of oxygen atoms = 2 × 3 = 3
M in M O 3 that combine with one atom of M 2
2
So, the valency of metal M in M O is three.
3
2
What is variable valency
Certain elements show more than one valencies. Such elements are said to
show variable valency.
