Ionic Charges and Rules

Atoms become stable when their outer shell (valence shell) is full, like noble gases. For example, magnesium has 12 protons and 12 electrons; it loses 2 electrons to achieve a full valence shell and become a stable ion.

Magnesium (Mg) has 12 protons and 12 electrons. It loses 2 electrons to achieve a full valence shell. This makes it a positively charged ion (cation) with a +2 charge.

Nitrogen (N) has 7 protons and 7 electrons. It needs 3 more electrons to fill its valence shell. So, it gains 3 electrons, becoming a negatively charged ion (anion) with a -3 charge.

Alkali metals (Group 1) have only one valence electron and easily lose it to achieve a full outer shell. This gives them a +1 ionic charge.

Alkaline earth metals (Group 2) have two valence electrons and lose them to become stable. This gives them a +2 ionic charge.

Inner gas elements (noble gases) have a full valence shell, meaning they are already stable. This makes their ionic charge zero.

Halogens (Group 17) have 7 valence electrons and tend to gain one electron to achieve a full outer shell. This gives them a -1 ionic charge.

Cations (positively charged ions) tend to have higher charges as you move right across the periodic table. This is because as you move right, the number of protons (and therefore the positive charge) increases.

The crossover rule helps to determine the formula of an ionic compound. For example, magnesium has a +2 charge and nitrogen has a -3 charge. The charges are swapped and become subscripts, creating the formula Mg3N2.

The crossover rule is a shortcut for determining the formula of an ionic compound. It involves writing down the symbols of the elements, crossing over their absolute values of ionic charges, and using the resulting numbers as subscripts. For example, Aluminium (+3) and Chlorine (-1) would become AlCl3.

Atoms achieve stability by having a full valence shell, the outermost electron shell. This can be achieved by either gaining or losing electrons.

Positively charged ions formed when an atom loses electrons.

Negatively charged ions formed when an atom gains electrons.

Elements in Group 1 of the periodic table tend to lose one electron to achieve a stable configuration, resulting in a +1 charge.

Elements in Group 2 of the periodic table tend to lose two electrons to achieve a stable configuration, resulting in a +2 charge.

Elements in Group 17 of the periodic table tend to gain one electron to achieve a stable configuration, resulting in a -1 charge.

Elements in Group 18 of the periodic table have a full valence shell, making them already stable. They do not form ions and have a charge of 0.

A shortcut for predicting the formula of an ionic compound by exchanging the absolute values of the ionic charges to become the subscripts of the elements.

A compound formed by the electrostatic attraction between oppositely charged ions.