Alkali Metals (Group 1)
Lithium, sodium, potassium, rubidium, caesium and francium: soft, silvery metals with a single outer electron they give away almost instantly.
What they have in common
Every alkali metal ends its electron configuration in ns¹. Losing that one electron leaves a stable noble-gas core, so these elements form +1 ions and are the most reactive metals on the table. Reactivity climbs down the group because the outer electron sits further from the nucleus and is shielded by more inner shells, so it takes less energy to remove.
They react with water to give hydrogen gas and a hydroxide (2Na + 2H₂O → 2NaOH + H₂), which is why they are stored under oil. Hydrogen sits above group 1 because it also has one electron, but it is a nonmetal and is not counted as an alkali metal.
- One valence electron (ns¹)
- Form 1+ ions
- Low density: Li, Na and K float on water
- Low melting points that fall down the group
- Lowest first ionization energies in each period
Alkali metals at a glance
| Element | Z | Mass | Configuration | Valence e⁻ | Charges | EN | Radius (pm) |
|---|---|---|---|---|---|---|---|
| Lithium (Li) | 3 | 6.941 | [He] 2s1 | 1 | + | 0.98 | 134 |
| Sodium (Na) | 11 | 22.99 | [Ne] 3s1 | 1 | + | 0.93 | 154 |
| Potassium (K) | 19 | 39.098 | [Ar] 4s1 | 1 | + | 0.82 | 196 |
| Rubidium (Rb) | 37 | 85.468 | [Kr] 5s1 | 1 | + | 0.82 | 211 |
| Cesium (Cs) | 55 | 132.905 | [Xe] 6s1 | 1 | + | 0.79 | 225 |
| Francium (Fr) | 87 | [223] | [Rn] 7s1 | 1 | + | 0.7 | — |
Questions students ask
Why are alkali metals so reactive?
They have one electron outside a noble-gas core. It is easy to remove (low ionization energy), and losing it gives a very stable ion.
Is hydrogen an alkali metal?
No. Hydrogen is placed in group 1 because of its 1s¹ configuration, but it is a nonmetallic gas.
Which alkali metal is most reactive?
Caesium is the most reactive one that can be studied in bulk. Francium is predicted to be similar, but it is so radioactive that only tiny amounts have ever existed at once.