Chloride chemistry. Chlorides are compounds that contain chlorine (Cl). From left-right these are the chlorides of elements from period three of the periodic table: sodium chloride (NaCl), magnesium chloride (MgCl2), aluminium chloride (Al2Cl6), all solids. Next are the two liquids: silicon chloride (SiCl4) and phosphorus (III) chloride (PCl3), and finally phosphorus (V) chloride (PCl5). NaCl is table salt. Important trends for the period three chlorides are falling melting points, and a change from ionic bonding and neutral pH (Na, Al) to acid pH and covalent bonding. The phosphorus chlorides demonstrate two oxidation states of phosphorus.