What is the chemical formula for the compound trinitrogen tetrachloride?

SCl_4_ (the bounding underscores are to denote the subscript 4). The prefix on the chloride in the name denotes 4 Cl. Since this involves 2 (two) non-metals, you must specify how many of each element are in the compound to resolve the ambiguity. This is largely due to the fact that this is not an ionic compound where you can derive the charges and match up the elements accordingly. This is probable more than one may have been asking for. However, it is good to have.