Atoms are the fundamental units of matter. Each atom consists of a positively charged nucleus of protons surrounded by a cloud of negatively charged electrons. When the number of protons equals the number of electrons, the atom is electrically neutral, yet it often seeks a more stable electron configuration by forming bonds with other atoms.
When an atom exchanges one or more electrons with another, it becomes charged and is referred to as an ion. If the ion is composed of a single atom, it is called a monatomic ion. Conversely, ions that contain two or more atoms are known as polyatomic ions.
Table salt (sodium chloride) illustrates the behavior of monatomic ions in everyday life. In solid NaCl, each sodium atom (Na⁺) is surrounded by chloride ions (Cl⁻), creating a crystalline lattice. When dissolved in water, the lattice dissociates into individual Na⁺ and Cl⁻ ions, making the solution an electrolyte that conducts electricity.
Other common monatomic ions include:
Ions carrying a positive charge, such as Na⁺, are called cations, while those with a negative charge, like Cl⁻, are anions.
Polyatomic ions arise when two or more atoms combine and share electrons, forming a charged entity. Notable examples include:
