Halogens
Definition and meaning of Halogens in chemistry.
Halogens are the six group 17 elements, fluorine, chlorine, bromine, iodine, astatine, and tennessine, defined by seven valence electrons and strong reactivity, especially toward metals, to form salts.
In more detail
Because each halogen atom needs only one more electron to complete a stable octet, halogens have high electronegativity and electron affinity, readily forming −1 halide ions or single covalent bonds. Reactivity and electronegativity decrease down the group as atomic radius increases, making fluorine the most reactive and electronegative element on the periodic table. In their elemental state, halogens exist as diatomic molecules (F2, Cl2, Br2, I2); at room temperature fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine and tennessine are intensely radioactive and exist only in trace or synthetic amounts.
Key facts
| Field | General Chemistry |
|---|---|
| Periodic table position | Group 17 (VIIA) |
| Members | F, Cl, Br, I, At, Ts |
| Valence electrons | 7 |
Chlorine gas reacts vigorously with sodium metal to form the ionic salt sodium chloride: 2Na + Cl2 → 2NaCl.
Frequently asked questions
Why are halogens so reactive?
With seven valence electrons, they need just one more to reach a stable noble-gas configuration, giving them strong electron affinity and, for the lighter members, very high electronegativity.
Are all halogens diatomic gases?
No, elemental halogens are diatomic (X2), but their physical state varies: fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature.