ICSE Class 8 Answered

• An atom is very small in size and it consists of the subatomic particles protons, neutrons, and electrons.
• They are so small that they cannot be seen even under the most powerful microscope.
• About one million atoms stacked up one over the other would roughly equal the thickness of a sheet of a paper.

Molecule:

• A molecule is a group of two or more atoms chemically bonded together. 
• Molecules can be formed either by the combination of atoms of the same element or of different elements.
• Thus, there are two types of molecules — molecules of elements and molecules of compounds.