The most reactive non-metals - from fluorine's unmatched reactivity to chlorine purifying water worldwide and iodine preventing disease
Halogens, meaning "salt formers," are the most reactive non-metallic elements in the periodic table. With seven valence electrons, they aggressively seek one more electron to achieve a stable octet, making them powerful oxidizing agents. This reactivity decreases down the group but remains significant enough that none exist freely in nature.
From fluorine's ability to react with nearly every element to chlorine's role in water purification that has saved billions of lives, from bromine's use in flame retardants to iodine's essential role in thyroid function, halogens have profoundly impacted human health and industry. Their compounds include common table salt, hydrochloric acid in our stomachs, and fluoride protecting our teeth.
Reactivity decreases down the group as atomic size increases and electronegativity decreases.
| Element | State at 20°C | Color | Melting Point (°C) | Electronegativity |
|---|---|---|---|---|
| Fluorine | Gas | Pale yellow | -220 | 3.98 (highest) |
| Chlorine | Gas | Yellow-green | -101 | 3.16 |
| Bromine | Liquid | Red-brown | -7.2 | 2.96 |
| Iodine | Solid | Purple-black | 114 | 2.66 |
| Astatine | Solid | Metallic | 302 | 2.2 |
Sodium chloride is essential for life, maintaining fluid balance and nerve function.
Potassium bromide was crucial in early photography and is still used in some applications.
Calcium fluoride is the primary source of fluorine and is used in optics and metallurgy.
Silver iodide particles are used to induce rainfall in cloud seeding operations.