Atoms bond to other atoms through their electrons. The following analogy will be used to help us understand how this occurs. Imagine that the atoms of different elements are like kids coming to school. Each of these "kids" come to school with a specific number of crayons. These crayons represent the outer electrons for that atom. Explain how the elements (kids) share, gain, lose their crayons (electrons) and bond to another so that they achieve stability.

All atoms (except for group 0 elements) of elements tend to achieve stability by having there outermost shell completely filled; achieving an octet configuration. During chemical bonding, atoms tend to achieve stability majorly in one of the two ways below

1) Ionic or electrovalent bonding: This involves the transfer of electrons from a positively charged ion (cation) to a negatively charged ion (anion). Here, no molecule is formed. For instance, in the formation of a sodium chloride (NaCl) salt. Sodium ion donates the single electron on it's outermost shell (to achieve it's octet configuration) to chloride ion (which needs just one more electron in it's outermost shell to achieve it's octet configuration).

Na⁺ + Cl⁻ ⇒ NaCl

2) Covalent bond: This involves the sharing of lone pair of electrons between two atoms to form a molecule. For example, the outermost shell of an oxygen atom, has two single electrons (that are not in pair), these single electrons can form covalent bond independently with hydrogen atoms (to form water) that also have just one electron in their shells. Hence, at every "covalent bonding site", an electron from oxygen and an electron of hydrogen is shared between the two atoms in order to achieve a stable configuration (Here, we have two "covalent bonding sites").