It is possible to predict whether an element will form a cation or anion by determining how many protons an element has. If an element has more protons than electrons, it is a cation. Elements with more electrons than protons form an anion. When two elements are mixed, the amount of ionization energy determines whether the new substance will turn into a cation or anion.
Regardless of how many protons an element has, it becomes an ion when one or more valence electrons is stripped from the atom. Ions are either negatively or positively charged. A cation is a positively charged ion and an anion is a negatively charged ion.
Each element has a certain amount of ionization energy. This is what determines the amount of energy that is required to strip away a valence electron. When combining two elements, it is necessary to identify the atomic number of the elements to determine if the mix will result in a cation or anion. Elements with lower atomic numbers can be easily stripped of a valence electron and are thus more prone to turning into a cation. Elements with a larger atomic number hold on to valence electrons and are typically anions. The atomic number is located above each element on the periodic table.