A Guide to the Halogens
Meet the highly reactive "salt-formers" of Group 17 on the periodic table.
What Are Halogens?
The halogens are a group of five chemically related elements in Group 17 of the periodic table. This group includes Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and the radioactive Astatine (At). The name "halogen" means "salt-producing," because they readily react with metals to form salts (e.g., Sodium Chloride - NaCl).
They are the most reactive group of nonmetals on the periodic table. In their pure form, they exist as diatomic molecules (F₂, Cl₂, etc.) and are too reactive to be found uncombined in nature.
Key Characteristic: Seven Valence Electrons
The defining feature of a halogen is its electron configuration. Every element in this group has seven electrons in its outermost shell (valence shell).
- They are just one electron short of a full, stable octet (like the noble gases).
- This makes them extremely eager to gain one electron, making them highly reactive and giving them a high electronegativity.
This tendency to attract an electron means they readily form a -1 ion (a halide ion, e.g., F⁻, Cl⁻) when reacting with metals.
How to Remember the Halogens
To remember the order of the first five halogens, you can use this mnemonic:
Funny Clowns Bring Interesting Animals.
(Fluorine, Chlorine, Bromine, Iodine, Astatine)
Location on the Periodic Table
The halogens are in the second-to-last column on the right of the periodic table, Group 17.
Properties and Uses of Halogens
The halogens show a clear trend in their physical properties as you move down the group.
| Element | State at STP | Color | Key Use(s) |
|---|---|---|---|
| Fluorine (F₂) | Gas | Pale yellow-green | Toothpaste (as fluoride), Teflon production, uranium processing. |
| Chlorine (Cl₂) | Gas | Yellow-green | Disinfecting water (pools, drinking water), bleach, PVC plastic production. |
| Bromine (Br₂) | Liquid | Red-brown | Flame retardants, pharmaceuticals, photography. |
| Iodine (I₂) | Solid | Gray-black solid | Antiseptic (tincture of iodine), dietary supplement for thyroid function. |
| Astatine (At) | Solid (presumed) | Unknown (highly radioactive) | No commercial uses due to its extreme rarity and radioactivity. Used in research. |
Key Takeaways
- Halogens are in Group 17 of the periodic table.
- They are defined by having seven valence electrons, making them highly reactive.
- They are the most electronegative (electron-attracting) group of elements.
- They exist as diatomic molecules in their pure form (F₂, Cl₂, etc.).
- They react with metals to form salts, such as sodium chloride (table salt).