Double Bond vs Single Bond | Sigma Bond vs Double Bond
As proposed by the American chemist G.N.Lewis, atoms are stable when they contain eight electrons in their valence shell. Most of the atoms have less than eight electrons in their valence shells (except the noble gases in the group 18 of the periodic table); therefore, they are not stable. These atoms tend to react with each other, to become stable. Thus, each atom can achieve a noble gas electronic configuration. This can be done by forming ionic bonds, covalent bonds or metallic bonds. Among these, covalent bonding is special. Unlike other chemical bonding, in covalent bonding there is a capability to make multiple bonds between two atoms. When two atoms having similar or very low electronegativity difference react together, they form a covalent bond by sharing electrons. When the number of sharing electrons is more than one from each atom, multiple bonds result. By calculating bond order, the number of covalent bonds between two atoms in a molecule can be determined.
What is Single Bond?
Single bond is formed when two electrons are shared between two atoms with similar or low electronegativity difference. The two atoms can be of the same type or different types. For example, when the same atoms are joined to form molecules like Cl2, H2, or P4, each atom is bonded to another by a single covalent bond. Methane molecule (CH4) has single covalent bond between two types of elements (carbon and hydrogen atoms). Further, methane is an example for a molecule having covalent bonds between atoms with very low electronegativity difference. Single covalent bonds are also named as sigma bonds. Groups bonded only by a sigma bond have the ability to undergo rotation about that bond with respect to each other. This rotation permits a molecule to have different conformational structures. Single bond is formed with sp3 hybridized atoms of a molecule. When two equal sp3 hybridized molecules are linearly overlapped, a single bond is formed.
What is Double Bond?
Double bond is formed when two atoms share two pairs of electrons between them in order to fill the valence orbitals. Double bonds are shorter than the single bonds, but stronger than them. Sp2 hybridization allows the atoms to form double bonds. Of these two bonds, one is a sigma bond made by the linear overlapping of two sp2 hybridized orbitals. The other bond, which is known as the pi bond, is formed by the lateral overlapping of two p orbitals. The common example for a molecule with a double bond is ethylene. In ethylene, double bond is between two carbon atoms. Other than between similar atoms, double bond is formed between different atoms as in the examples of the carbonyl carbon (C=O), imines (C=N), azo compounds (N=N) etc.
What is the difference between Single bond and Double bond?
• In single bond formation, only one electron pair is shared between two atoms, whereas in forming double bonds two electron pairs are shared.
• Single bonding results from overlapping two sp3 hybridized orbital. Double bonds result from linear overlapping of two sp2 hybridized orbitals and by lateral overlapping of p orbital.
• Single bond contains one sigma bond, whereas double bond contains one sigma bond and one pi bond.
• Length of the single bond is higher than that of the double bond.
• Double bond dissociation energy is relatively higher than the single bond dissociation energy.