Metal ions are charged particles formed when metal atoms lose one or more electrons. These ions can carry a positive charge, known as cations, and are essential in various chemical reactions. Common examples include sodium ions (Na⁺) and calcium ions (Ca²⁺), which play crucial roles in biological processes. In nature, metal ions are found in minerals and are vital for many functions in living organisms. They are involved in enzyme activity, cellular signaling, and the formation of structures like hemoglobin, which transports oxygen in the blood. Understanding metal ions is important in fields like biochemistry and environmental science.