Question

What are single and double covalent bonds?

Answer 1

Single bonds are overlap of one pairs of orbitals (sharing of 2 valence electrons between two atoms); double bonds require overlap of two pairs of orbitals (2 pairs of shared electrons)

Explanation:

In a single bond, one valence orbital of each atom overlaps in space. This will be a sigma bond. Most often, the orbitals involved are s- or p- orbitals.

In a double bond, the atoms each have two orbitals overlapping - generally one s- orbital and one p-orbital (a sigma and a pi bond), or it can be two p-orbitals (two pi bonds).

It is possible for the same two atoms, in different compounds, to form single double or (especially in the case of carbon) a triple bond.
An example would be the C-to-C bond in ethane or ethene.

When chemists analyze the nature of these bonds, they find that single bonds are longer and weaker than double bonds. By longer, we mean the distance from nucleus to nucleus is greater in the bonded atoms. By weaker, we mean less energy is required to break the bond. This follows from the idea that if only one pair of electrons is being shared between atoms, the electric force between electrons and nuclei is smaller than if you had two pairs of electrons.