Nature and size of molecule

The Nature and Size of Molecules

All matter is made up of tiny particles called molecules. These molecules themselves are made up of tinier particles called atoms. Both molecules and atom are too tiny to be seen with the naked eyes.

One mole of every substance is believed to contain about 6.02 × 1023 molecules. One molecule of a substance could be found from the combination of two or more elements of that substance.

Definition of Molecule

Hence, we define a molecule as “the smallest unit of matter that is capable of independent existence”. This means that a molecule of a substance could exist alone.

Definition of Atom

An atom is defined as the smallest unit of matter that can take part in a chemical reaction and is not capable of independent existence.

Definition of Element

An element is any substance in which everything could be built up. It is a substance which consists of only one kind of matter and cannot be broken down into anything simpler by any chemical means.


  1. (a) Define the following terms: (i) Molecule (ii) An atom (iii) An element.
  2. Which of the above is capable of dependent existence?
  3. Which of them is capable of independent existence?


  1. Differentiate an atom from a molecule.
  2. Highlight the states of matter.
  3. Enumerate the factors capable of influencing diffusion rate.
  4. What were the evidences to prove the particulate nature of matter?

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