(a) Atom:

i. The building blocks of all matter are atoms. Atoms are very small.

ii. They are smaller than anything we can imagine or compare with.

(b) Molecule:

i. A molecule is general a group of two or more atoms that are chemically bonded together. They are tightly held together by attractive forces.

ii. A molecule can be defined as the smallest particles of an element or a compound that is capable of an independent existence.

iii. A molecule shows all the properties of a particular substance.

iv. Atoms of the same element or different element join together to form molecules.

(c) Avogadro’s number:

i. Avogadro’s number is the number of particles (atoms, ions or ions) present in one mole of any substance is fixed with a value of 6.022 × 10²³.

ii. This is an experimentally obtained value.

(d) Valency:

i. The combining power or capacity of an element is known as valency.

ii. Valency can be used to find out how the atoms of an element will combine with the atoms of another element to form a chemical compound.

(e) Molar mass:

Molar mass is the mass of one mole of any substance. One mole of any species (atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecules mass in grams.

Molar mass is represented by “M”

We can write,

Molar mass (M) = mass (m) × Number of moles(n)