Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. Covalently bonded metal halides may be discrete molecules, such as uranium hexafluoride, or they may form polymeric structures, such as palladium chloride. The halogens can all react with metals to form metal halides according to the following equation: 2M + nX2 → 2MXn where M is the metal, X is the halogen, and MXn is the metal halide. * Sodium chloride crystal structure * Discrete UF6 molecules * Infinite chains of one form of palladium chloride