A double covalent bond consists of two pairs of shared electrons. It is formed by the sharing of two pairs of electrons between two atoms. It is actually a combination of two single bonds. It is represented by putting two short lines between the two atoms [=].
Let us take few examples to understand the double covalent bond in the oxygen molecule.
The oxygen atom cannot exist on its own. It does not have a stable, inert gas electron arrangement. Oxygen gas does not consist of a single atom, but consists of two atoms, which join to form a molecule.
----- electronic configuration = 2,6
Atomic number of oxygen is 8, electronic configuration is 2,6. It needs two more electrons to attain the inert gas configuration. The oxygen atom shares two of its valence electrons with another oxygen atom to form a diatomic oxygen molecule. Each of the oxygen atoms in the covalent molecule consist of eight electrons in the valence shell.
A double covalent bond is stronger than a single covalent bond.
An ethylene molecule (Ethene)
A molecule of ethylene consists of only carbon and hydrogen atoms. It is a hydrocarbon. It has a chemical formula C2H4. What type of covalent bonding is present in this compound?
Carbon:
Electronic configuration is 2,4. It needs four more electrons to complete its octet.
Hydrogen:
Electronic configuration is 1 . It needs one more electron to complete its duplet.
The carbon atom has achieved the electronic configuration of neon and hydrogen, that of helium atom.
Diagrammatically it can be represented as shown below:
