Atoms are made up of an atomic nucleus and electrons.
Electrons far from the atomic nucleus may easily fall off, or electrons from outside may enter. If a neutral atom loses an electron, the amount of (+) charge becomes relatively larger, resulting in a (+) charged particle. On the contrary, when a neutral valence electron is obtained, the amount of (-) charge becomes relatively larger, so it becomes a particle with a negative charge.
In this way, the particles charged by losing or gaining electrons depending on the type of atom are called ions, ions with (+) charges are called 'cation', and ions with (-) charges are called 'anions'.
Display of ions
When referring to an ion, the number of electrons lost or gained and the type of charge is displayed in the upper right corner of the element symbol.
For example, a sodium ion resulting from the loss of one electron by a sodium atom is represented by Na+, and a copper ion resulting from the loss of two electrons by a copper atom is represented by Cu2+.
Besides, chloride ions obtained by obtaining one electron by a chlorine atom are represented by Cl-, and sulfide ions formed by obtaining two electrons by a sulfur atom are represented by S2-.
Ionic binding matter
Matters made of ions can be bonded together by the electric force. The ionic binding force is quite strong, so ionic binding substances usually exist in a solid-state at room temperature. However, it also has the property of being easily soluble in polar solvents such as water.
The solid ionic substances are tightly bonded to each other and become a non-conductor in which electric current cannot flow. However, when ionic substances are dissolved in a solvent, they can move easily and become a conductor in which the electric current flows well.