Question

What is a definition of a molecule?

Answer 1

Hint: An atom is the simplest and the smallest part of any substance. Atoms contribute to bond together through various bonds and form molecules. Molecules contain various atoms combined in certain quantities with the help of chemical bonding. The charge of a molecule is zero that means it is neutral in nature.

Complete answer:
A substance comprises various small units called atoms. These are the simplest units of any material or compound. The atoms made up a molecule. A molecule is said to contain the same or different atoms in a quantity of two or more than two. A molecule consists of various atoms held together by chemical bonds between the atoms.
The bonding between different or same atoms is a result of the valence electrons present in the atoms. These electrons can be shared by the atoms to form bond pairs that are called covalent bonds. A molecule is said to be neutral species without having any charge because the atoms bond in such a way to satisfy their octet and the full configuration of their outer shell, that give any molecule electrical neutrality.
Examples of molecules are carbon dioxide,$C{{O}_{2}}$, methane $C{{H}_{4}}$etc.
Hence, a molecule is defined as the chemical species containing two or more than two atoms which are chemically bonded to each other and completes their octet by sharing electrons that gives the molecule electrical neutrality.

Note:
Ionic compounds are formed by transfer of electrons, they consist of ionic bonds. The ionic compound does not form as a result of molecules or atoms as they contain ions called cations and anions. Cations are formed by donating electrons and anions are formed by gaining electrons. For example, NaCl consists of ions $N{{a}^{+}}$ and $C{{l}^{-}}$.