"Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a 
hydrocarbon and the simplest alkyne.[2] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution."
"As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carbon-carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group."
"In terms of valence bond theory, in each carbon atom the 2s orbital hybridizes with one 2p orbital thus forming an sp hybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap to form a strong σ valence bond between the carbons, while on each of the other two ends hydrogen atoms attach also by σ bonds. The two unchanged 2p orbitals form a pair of weaker π valence bonds. "