covalent bond - definition, properties and examples

 A covalent bond can be define as a chemical bond which results when electrons are shared by two atoms. It only takes place between two non-metal atoms. 

When two atoms involved in a chemical bond formation do this through the sharing of the electrons in their outermost valence shell to achieve octet of electrons, covalent bonds are produced. Each covalent bond is formed from a pair of electrons, each of which is donated by each of the atoms involved in the bond formation. 

We will both explain the sharing of electrons in both non-metal elements and non-metal compounds.

Covalent bonds in non-metal elements

1. Hydrogen  

A hydrogen atom has only one shell, with one electron. The shell is capable of accommodating up to two electrons. When two hydrogen atoms get close enough, their shells overlap and then they can share electrons. Like this:

So each has gained a full shell of two electrons, like helium atoms. Each hydrogen atom has a positive nucleus. Both nuclei attract the shared electron - and this strong force of attraction holds the two atoms together. This force of attraction is called a covalent bond. A single covalent bond is formed when atoms share two electrons. 

The two bonded hydrogen atoms above form a molecule. A molecule is a group of atoms held together by covalent bonds. Since it is made up of molecules, hydrogen is a molecular element. Its formula is H2. The 2 tells you there are 2 hydrogen atoms in each

molecule.

2. Oxygen

An oxygen atom has six outer electrons, so needs a share in two more. So

two oxygen atoms share two electrons each, giving molecules with the

formula O2. Each atom now has a stable outer shell of eight electrons:

Since the oxygen atoms share two pairs of electrons, the bond between them is called a double bond. You can show it like this: O5O.

3. Chlorine

A chlorine atom needs a share in one more electron, to obtain a stable outer shell of eight electrons. So two chlorine atoms bond covalently like this:

Since only one pair of electrons is shared, the bond between the atoms is

called a single covalent bond, or just a single bond. You can show it in a

short way by a single line, like this: Cl2Cl.

Covalent bond in non-metal compounds

In a molecular compound, atoms of different elements share electrons.

The compounds are called covalent compounds. Here are three examples.

1. Hydrogen chloride(HCL)

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The chlorine atom shares one electron with the hydrogen atom. Both now have a stable arrangement of electrons in their outer shells: 2 for hydrogen (like the helium atom) and 8 for chlorine (like the other noble gas atoms). 

2. Water(H2O)

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The oxygen atom shares electrons with the two hydrogen atoms. All now have a stable arrangement of electrons in their outer shells: 2 for hydrogen and 8 for oxygen. 

3. Methane(CH4)

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The carbon atom shares electrons with four hydrogen atoms. All now have a stable arrangement of electrons in their outer shells: 2 for hydrogen and 8 for carbon.