How Atoms Combine

In universe every thing tries to stabilize itself, likewise atoms also combine with one other, due to an inherent tendency to stabilize themselves. They get their stabilization by losing, gaining or sharing electrons to attain nearest noble gas configuration. The tendency of an atom to attain maximum eight electrons in the valence shell is known as octet rule. In periodic table only noble gases follow this rule because of this they are inert and dose not react with each other. Thus these gases are most stable of all elements. There are many ways that atoms can combine, when atoms combine, only electrons in the outer (valence) shell are involved. Atoms combine with each other forming following bonds.

There are two types of bonds: ionic and covalent bond. Ionic bond occurs between metals and non metals while covalent bonding occurs between two non metals.

• IONIC BOND

According to the lewis theory, ionic bond is formed by the complete transfer of electrons from an atom with low ionization energy to another atom with high electron affinity. 

• COVALENT BOND

A covalent bond is formed by the mutual sharing of electrons between two non metal atoms.  While sharing, each atom completes its valence shell and attains the inert gas configuration. A covalent bond may be non-polar or polar in the character.

• Non-polar covalent bonds

In such bonds, the bonding electron pairs are equally shared between two atoms having same electronegativities. Due to even distribution of charge, the bonded atoms remain electrically neutral. Such kind of bonds are mostly formed in homonuclear compounds.

•  Polar covalent bonds

When two different atoms are joined by a covalent bond, the electron pair is not equally shared between the bonded atoms. The bonding pair of electrons will be displaced towards the more electronegative atom. This would make one end of the molecule partially positive and the other partially negative forming two poles.