13.0 Physical Properties

(1.) Acetylene is a colourless gas with ethereal smell in pure state; b. pt.$ = - {84^o}C$

(2.) Liquified acetylene is explosive and burns with a luminous smoky flame due to high carbon content hence it is used for lighting purpose.

(3.) As the s – character of the orbitals involved in bonds increases from 25 percent $(s{p^3})$ to 33.3 percent $(s{p^2})$ to 50 percent (sp), the electrons in those orbitals are on the average, close to carbon nucleus and this leads to a contraction in the internuclear distance.

Bond lengths are in the order

$$C \equiv C < C = C < C - C$$