Anion
An anion is an atom or molecule with a net negative electric charge, usually because it has gained electrons.
Electron affinity: The energy change when a neutral atom or molecule gains an electron. Electron affinity helps determine whether an atom tends to form an anion.
Electron: A negatively charged subatomic particle found in atoms and molecules. Anions have more electrons than protons, giving them their net negative charge.
Halide: A binary anion formed from a halogen element, such as chloride or bromide. Halides are common anions in salts and chemical reactions.
Neutral atom: An atom with equal numbers of protons and electrons and no net electric charge. An atom becomes an anion when electron gain makes its charges unequal.
Ionization energy: The energy required to remove an electron from an atom or molecule. Unlike electron gain, electron removal usually creates a positively charged ion.
Atomic nucleus: The dense central region of an atom, containing protons and usually neutrons. An anion’s nucleus remains positively charged while its electron count increases.
Polyatomic ion: A charged group of covalently bonded atoms that behaves as one ion. Many familiar anions, including nitrate and sulfate, contain several atoms.
Ion: An atom or molecule with a net electric charge from an imbalance of protons and electrons. Anion is the negatively charged member of the broader ion family.
Cation: An atom or molecule with a net positive electric charge, often formed by losing electrons. Anions carry the opposite charge, and the two often attract each other.
Atomic number: The number of protons in an atom’s nucleus, which determines the element. Gaining electrons changes charge, not the atomic number or element.