A monoatomic ion is one that forms from a single atom. Ions with a positive charge, such as sodium (Na+) are cations. Those with a negative charge, such as chlorine (Cl-) are anions. Monoatomic ions are also known as simple ions.
Ions form by gaining or losing electrons. In neutral atoms, the number of protons and electrons are equal. This gain or loss of electrons results in a positive or negative electrical charge. Ions form in several ways. Ionic compounds that dissolve in water dissociate into cations and anions while in solution. Ions form when atoms are bombarded with radiation. When certain ionic compounds melt, ions form in the liquid.
Substances that ionize in water are electrolytes. Pure water is a poor conductor of electricity. However, a water solution containing electrolytes conducts electricity. As the water evaporates, the ions join to form neutral compounds again. However, if other ions are present, they sometimes join to form new compounds. If an acid neutralizes a base, the H+ ions join the OH- ions to form water. The remaining ions form a salt. Certain ions combine in solution to form an insoluble material and precipitate out of the solution. In precipitation reactions, the ions not involved in the precipitate remain in solution.