Rule 1

Write the symbol for the more metallic element first. Then, write the symbol for the non-metallic element.

Rule 2

Write the combining capacities for the elements. (The numbers can be found on the periodic table)

Rule 3

Subscripts are used to indicate the number of atoms each element has in that compound. (if the element has only one atom, then no subscript is needed for that element) Then, criss-cross the number of the combining capacity.