Animation of the bonding in a molecule of ethyne, or acetylene, (C2H24), which contains a triple bond. Initially there are two carbon atoms, each with full 1s and 2s electron orbitals (spheres), and one electron each in two 2p orbitals (green and orange). These then undergo sp hybridisation, in which a 2s electron is promoted to the third vacant 2p orbital (red). One of the 2p orbitals and the 2s orbital then hybridise, merging to form two sp orbitals (blue) arranged in a linear geometry. Two 2p orbitals (green and orange) remain unhybridised. A hydrogen atom then forms a covalent bond (blue) with one sp hybrid orbital on each carbon, while the second sp2 hybrid forms a bond (centre) with its equivalent on the other carbon. These are called covalent s bonds. The formation of the carbon-carbon s bond brings the carbon atoms closer together, so the remaining 2p orbitals are very close. The adjacent 2p orbitals on the carbons then form a different type of bond, called a pi bond (red and pink arcs), one above and below the carbon atoms, and one in front and behind it. The pi bonds in addition to the s bond forms what is known as a triple bond between the carbon atoms.