Question

What are the main three ways in which an atom can obtain stable chemical stability?

Answer 1

An atom obtains stability by having stable electronic configuration, i.e; by having 2 electrons (for H, Li,Be) or 8 electrons in its valence shell. An atom can get stable configuration by following ways:

Mutual sharing of electrons: In mutual sharing of electrons, two atoms contribute one electron for one bond called as covalent bond. The electrons are now counted as the electrons of both the atoms and in this way the atom obtains stable configuration.

Example: Hydrogen has one electron in its valence shell and need one more electron for getting stable configuration. Two hydrogen atoms come closer to each other and share their electrons forming one covalent bond. So, two electrons of this bond will be counted for both the atoms hence each atom has two electrons.

Similarly H can share its electron with F or Cl which have 7 electrons in their valence shell. The two shared electrons will belong to both the atoms and hence will get stable configuration

2: By loss of electrons: An atom can loose electron(s) to form a cation so that it gets stable configuration. Example: Na atom electronic configuration 2,8,1. Thus, it needs seven electrons to have eight electrons in its valence shell. It can't form one covalent bond because that will give it two electrons instead of 8. It looses its one electron to get configuration of 2,8. Thus, forming Na⁺ ion with stable configuration.

3) By gaining electrons: An atom can also get stable configuration by gain of electrons forming an anion with stable configuration.

Example: Flourine with seven electrons in its valence shell can accept an electron from Na (or any other atom which itself changes to cation) and hence changes to F^- which has 8 electrons in its shell.

The cation and anions formed by gain and loose of electrons are held together by ionic bond

Note: usually a non-metal forms covalent bond with non-metal while a metal and non-metal form ionic bond