What Are Alkali Metals?
The alkali metals are a fascinating group of elements that sit in Group 1 of the periodic table — the very first column on the left-hand side. They include six elements that you'll encounter in chemistry:
- Lithium (Li) — atomic number 3
- Sodium (Na) — atomic number 11
- Potassium (K) — atomic number 19
- Rubidium (Rb) — atomic number 37
- Caesium (Cs) — atomic number 55
- Francium (Fr) — atomic number 87
Despite being called metals, alkali metals behave very differently from the metals you're probably used to — like iron or copper. They are soft, highly reactive, and have surprisingly low densities. In fact, lithium, sodium, and potassium are all less dense than water, meaning they float!
The elements in Group 1 of the periodic table (Li, Na, K, Rb, Cs, Fr). They are soft, low-density metals that react vigorously with water to form alkaline (basic) solutions.
The name 'alkali' comes from the Arabic word al-qaly, meaning 'plant ashes'. When alkali metals react with water, they form alkaline solutions — which is exactly how they got their name.
Electronic Structure: The Key to Reactivity
To understand why alkali metals behave the way they do, you need to look at their electronic configuration — the arrangement of electrons in their shells.
Every alkali metal has exactly one electron in its outermost shell. This is the defining feature of Group 1 elements:
| Element | Electronic Configuration | Outer electrons |
|---|---|---|
| Lithium (Li) | 2, 1 | 1 |
| Sodium (Na) | 2, 8, 1 | 1 |
| Potassium (K) | 2, 8, 8, 1 | 1 |
This single outer electron is very easy to lose — and that's the whole story of alkali metal reactivity! Atoms 'want' to have a full outer shell, and the quickest way for an alkali metal to achieve this is to give away that one lonely electron.
The electron(s) in the outermost shell of an atom. Alkali metals each have exactly one valence electron, which they readily lose to form +1 ions.
Imagine you're carrying a backpack with just one item left in it. It's much easier to just hand that one item to someone else than to try filling the bag up with more things. That's exactly what alkali metals do — they 'hand off' their single outer electron rather than trying to gain seven more.
10 more sections in this topic
Pick this up in your Library: it holds the whole topic, notes, cheatsheet and questions.