At this point, you've learned that the electron configurations of elements are not permanently fixed. According to the octet rule, atoms gain or lose electrons to achieve more stable electron configurations. For example: a magnesium (Mg) atom has 12 electrons, two of which are in its highest energy level, so a magnesium atom has two valence electrons. An atom with two valence electrons is reactive. To become stable, a magnesium atom loses its two valence electrons, forming an ion with a charge of 2+.
In the notation for an ion, the chemical symbol of the element is written first, then the charge of the ion is written as a superscript. So, the proper notation for the magnesium ion is Mg2+.
In ion notation, the number 1 is not written. For example, a potassium (K) ion has a charge of +1, so it is written as K+, not K1+ .
Question
How does the charge of an ion relate to the octet rule?
Ionic charges show how many electrons an atom has gained or lost to achieve a full outer energy level. For example, magnesium has two valence electrons and loses both to have a stable octet, forming a Mg²⁺ ion. Similarly, atoms that gain electrons become negatively charged ions to complete their octet.
