subject: Double Covalent Bond [print this page] Atoms can form molecules by sharing electrons, e.g.H2, Cl2, HCl, H2O molecules are formed by sharing of electrons. Each atom in such molecules acquires stable electronic configuration after sharing one or more valence electrons. They do so to acquire the nearest noble gas configuration. Let us consider the example for the formation of Hydrogen molecule. The electronic configuration of H is 1. Each hydrogen atom needs one more electron to complete its duplet and to acquire the noble gas configuration of He. A H atom can complete its duplet by sharing one valence electron with another H atom. The shared pair of electrons will be attracted by the nuclei of both the hydrogen atom.
Double bond structure:
Double bond is a covalent bond between the two chemical elements which involves four bonding electrons. These bonds have two pairs of shared electrons. It shares two pairs of electrons between two atoms. Normally it is a combination of 2 single bonds. Between two atoms, two short lines are put and this is the representation of double bond.
Examples for double bond structure:
To understand this, we take an example of oxygen molecule.
Oxygen atom does not contain inert gas and stable electronic arrangement. There is no single atom present in oxygen gas. It contains two atoms and joins forming a molecule.
The oxygens atomic number is 8 and the electronic configuration is 2, 6. To gain the configuration of inert gas, it requires two more electrons. For the formation of diatomic oxygen molecule, there is a sharing takes place between the two valence electrons of oxygen atom with another oxygen atom. Now each oxygen atom present in covalent molecule has eight electrons in valence shell.
The double bond is stronger than single bond.
Hybridization in double covalent bond:
In ethane, before the formation of bonds, carbon atoms used to hybridize their outer orbitals, and now they hybridize only three of the orbitals rather than four. They utilize 2s electron and two of the 2p electrons and leave other 2p electron unchanged.
Electronics configuration box
The formation of new orbitals occurs which is known as sp2 hybrids. It is said sp2 because it is made by one s and two p orbitals which reorganize themselves. The arrangement of three sp2 hybrid orbitals is at 120o to each other in a plane. The other p orbital is present at the right angles to them.
hybride orbital single
In ethene, two carbon atoms and 4 hydrogen atoms look like this before the joining of both.
hybride orbital double
Double bonds are shorter than single bonds. The bond order of this is two. They are electron rich which is helpful in making them reactive.
Double Covalent Bond:
A bond formed by sharing of one pair of bond of electrons between two atoms, is called Single covalent bond. When two atoms share two pairs of electrons, the bond formed between them is called Double Covalent Bond. For example there is double bond between two oxygen atoms in oxygen molecule. Oxygen in air does not exist as a single atom. It has two oxygen atoms, which combines together to form molecule.
Let us consider the double covalent bond of oxygen molecule in more details. The atomic number of oxygen is 8. It has electronic configuration of 2,6. Each oxygen atom needs two more electrons to complete its octet and to acquire the noble gas configuration of Ne. An Oxygen atom can complete its octet by sharing two valence electron with another oxygenatom. The shared pair of electrons will be attracted by the nuclei of both the oxygen atoms. When two atoms share two pairs of electrons, the bond so formed is called Double Covalent Bond. Here four electrons of each oxygen atom are being shared, for the formation of this double covalent bond.
covalent bond
Few another Examples of Double Covalent Bond
Double covalent bond is also formed in many molecules. For example ethene[C2H4] molecule has carbon-carbon double bond in it. Carbon dioxide[CO2] has double bond in between carbon and two oxygen atoms. Water molecule[H2O] is another common example of double covalent bond.
