1. Each carbon is only joining to two other atoms rather than four or three.
2. Here the carbon atoms hybridise their outer orbitals before forming bonds, this time they only hybridise two of the orbitals.
3. They use the ‘s’ orbital (2s) and one of the 2p orbitals, but leave the other 2p orbitals unchanged.
4. The new hybrid orbitals formed are called sp-hybrid orbitals, because they are made by an sorbital and a p-orbital reorganizing themselves.
