Formation Of Ions

Formation of cations

When an atom loses one or more electrons, it becomes a positively charged particle called a cation.

In a Lithium atom, there are 3 protons and 3 electrons. In a lithium ion, there are 3 protons and 2 electrons. Therefore, the lithium ion carries an overall positive charge of 1+ and is written as Li+.

Formation of anions

When an atom gains one or more electrons, it becomes a negatively charged particle called an anion.

In a Fluorine atom, there are 9 protons and 9 electrons. In a Fluoride ion, there are 9 protons and 10 electrons. Therefore, the fluoride ion carries an over positive charge of 1- and is written as F-.

So why do atoms become ions?

Atoms need to become ions so that it can obtain a full valence shell and hence bond with other elements via ionic bonding. Ions can lose or gain up to 3 electrons to obtain a full valence shell. This also means that any atom with a valency of 4 can never become an ion.

Charges on the ions are related to the group number and number of valence electrons. Elements on the left side of the Periodic Table lose their valence electrons to form cations with charges corresponding to their group number, while elements on the right side of the periodic table gain electrons to form anions corresponding to their group number to fill their valence shells with 8 electrons.