I thought that as a general rule when writing out compound names (in full) involving a coordination metal, the charge of the coord metal must be stated in Roman Numerals. If nothing is specified than a charge of +1 is assumed. But I came across a compound involving zinc written zinc..... without any roman numeral so I assumed it had +1 charge when bound within the compound. But it turned out to have +2 charge. Why don't they specify it by writing zinc(II)..... ?