Like us, different element have different number of such twins.

They together form a molecule of the element.

The number of atoms forming a molecule is called the atomicity of the element.

E.g. H2, P4

Types of Molecules

If the molecule of an element contains 1 atom it's called a monoatomic molecule.

E.g. Na, He, etc.

If the molecule of an element contains 2 atoms it's called a diatomic molecule.

E.g. O2, N2

If the molecule of an element contains more than 2 atoms it's called a polyatomic molecule.

E.g. P4, S8

Combining Power

Atoms combine with each other or atoms of other elements in whole numbers, this number is called the combining power or combining capacity of the element.

E.g. Combining power of oxygen is 2 and hydrogen is 1. Hence, they combine together to form water H2O, where the numbers indicate the number of atoms of each element.

Combining Powers
of Elements

Fe = 3

O = 2

Cl = 1

K = 1

Zn = 2

S = 2

Ca = 2

Na = 1

Access All Content

Video Explanations, Practice Worksheets and Solved Examples for all Chapters.
Textbook solutions, Formulae and Mindmaps across all boards.

More from Grade 5 Science


Understand the concepts of water on earth, its sources and groundwater.


How do plants make their food? Get inside the plant to understand the process of photosynthesis.


Visit the depths of the Earth to see the birth of a rock! Learn about the different types of rocks, igneous, sedimentary and metamorphic, and how they're formed.