Phosgene. Molecular model of the inorganic compound phosgene (C.O.Cl2). A colourless gas, it killed tens of thousands during its use as a chemical weapon in World War I. It is an acyl chloride, oxohalide, and non-metal halide. Atoms are represented as spheres and are colour-coded: carbon (grey), oxygen (red) and chlorine (green). Illustration.