If element X is a halogen, then it belongs to the group 17 (or VIIA, under a different notation).
For each extra unit of atomic number, the group number increases by 1. That means that the X+1 element would belong to the group 18 (or VIIIA). <em>The X+2 element would thus belong in the group 1 </em>(or IA) one period higher (higher as in numeric value, not as in position in the periodic table).
<span>Gloria is writing the
chemical formula for a compound using its chemical name. She has just
identified the names of the elements in the compound. The tool that she will
need to use next is a textbook to learn the IUPAC naming of compounds or a
handbook of chemical compounds.</span>
