To name compounds and to determine molecular formulae from names a knowledge of the periodic table is helpful. The periodic table is arranged by grouping together elements that react alike. For reasons we will discuss later, elements react until the element achieves an electron configuration of a noble gas.
Elements can achieve a noble gas electron configuration three ways.
An element can give up electrons to achieve the electron configuration of the next lowest noble gas. An element can attract additional electrons to achieve the electron configuration of the next highest noble gas. K loses an electron so that it will have the same electron configuration as Ne. On the other side of the periodic table elements gain electrons to resemble the next higher noble gas. Metallic elements of groups 14,15, and 16 do not tend to form negatively charge ions.