Ethene molecule. Computer model showing the structure of a molecule of the hydrocarbon ethene (ethylene). Ethene is a colourless flammable gas and is the simplest of the alkenes (hydrocarbons with carbon-carbon double bonds). It is the most important starting product in the petrochemical industry and is the raw material for a wide variety of products. Atoms are shown as colour-coded spheres, with the bonds between them as rods. Carbon: black, hydrogen: white.