Bond strength is the energy required to break a bond. In a single bond, there is one shared pair of electrons between two atoms. In a double bond, there are two shared pairs of electrons between two atoms. The more electrons that are shared, the stronger the bond. This is because the more electrons that are shared, the more the electrons are attracted to the positively charged nuclei of the atoms.

The bond length is also a factor in bond strength. The shorter the bond length, the stronger the bond. This is because the shorter the bond length, the closer the atoms are to each other and the more the electrons are attracted to the positively charged nuclei of the atoms.

In general, a double bond is stronger than a single bond because there are more shared electrons and the bond length is shorter.