Physics – 5.1.1 The atom | e-Consult
5.1.1 The atom (1 questions)
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An atom forms a negative ion (anion) by gaining one or more electrons. When an atom gains electrons, the number of electrons exceeds the number of protons in the nucleus, resulting in a net negative charge. The atom becomes an anion. The number of electrons gained determines the charge of the anion. For example, if an atom gains one electron, it becomes a -1 ion (anion); if it gains two electrons, it becomes a -2 ion, and so on.
Example: Chlorine (Cl) is a halogen and commonly forms anions. Chlorine readily gains one electron to form a chloride ion (Cl-), which has a charge of -1.