Question

How do single, double and triple bonds form?

Answer 1

Chemical bonds (single, double or triple) are the force of attraction between multiple atoms which results in formation of compounds. For example, when a bond is formed between two hydrogen atoms, a hydrogen molecule (${H_2}$) is formed. Bonds can be formed due to attractive force between oppositely charged ions (resulting in ionic bonds, for e.g., in NaCl) or sharing of electrons between two atoms (covalent bonding, for e.g., in $C{H_4}$). Covalent bonds can be classified into single, double or triple bonds depending upon the number of electrons shared between two atoms.

Complete step-by-step answer:
Single Bond: A covalent bond formed between two atoms is called a single bond if each of the atoms shares one electron towards the bond formation. For example, in ${H_2}$ molecule, each hydrogen atom shares 1 electron towards formation of bond and thus a single bond is formed between the two hydrogen atoms (to give hydrogen molecule, ${H_2}$). Other molecules having single bonds are $N{H_3},C{H_4},\,{F_2},\,C{l_2}$ etc.

Double Bond: A double bond is formed between two atoms when each of the atoms shares two electrons towards bond formation, i.e., total four electrons are shared. For example, during formation of ${O_2}$ molecules from oxygen atoms, each atom shares two electrons and thus a double bond is formed between the two atoms. Other molecules having double bonds are alkenes.

Triple Bonds: A triple bond is formed when each of the participating atoms shares three electrons for bonding. Thus, total six electrons are shared. Compounds involving triple bonds are ${N_2},\,{C_2}{H_2}$ etc.

Additional Information:
Covalent bonds are formed on sharing of electrons and this sharing occurs by overlapping of the orbitals occupied by these electrons. During the formation of a single bond, head-to-head overlap of the orbitals containing the electrons occurs and the resulting bond is called sigma bond.

But as only one head-to-head overlap is possible, when more than one bonds (double or triple) are formed, the other orbitals do sidewise overlap and the bonds formed due to this sidewise overlapping are called pi bonds. Thus, in case of a double bond, one bond is sigma and other is pi. Similarly, in case of triple bond, one bond is sigma and the remaining two are pi.

Note: The strength of a covalent bond depends upon the extent of overlap between orbitals (higher is the overlapping, stronger will be the bond). As head-to-head overlapping always occurs more effectively than sidewise overlapping, so the sigma bond (formed due to head-to-head overlap) is stronger than pi bond (formed due to sidewise overlap). Thus, in case of a compound containing double bond, the pi bond(weaker) is broken first and then the sigma bond(stronger) breaks.