👉 In physics and chemistry, a kation (from the Greek word "kata" meaning "thing") is an atom or molecule that possesses a negative charge. They are often referred to as ions because they can act as carriers of electrical charges within their respective compounds. An example of an ion is water (H2O), which has two types of ions: hydrogen and oxygen. In addition, the chemical formula for sodium chloride (NaCl) contains one sodium (Na) and one chlorine (