Silicon Halides. Silicon reacts with halogens to form compounds of the form SiX4, where X represents any common halogen. At room temperature, SiF4 is a colorless gas, SiCl4 is a colorless liquid, SiBr4 is a colorless liquid, and SiI4 forms colorless crystals. SiF4 and SiCl4 can be completely hydrolyzed, but SiBr4 can be only partially hydrolyzed.