This group 1 alkali metals GCSE chemistry guide covers lithium, sodium, potassium, rubidium, caesium and francium — soft, shiny metals that react vigorously with water and get more reactive down the group, because each atom's single outer electron sits further from the nucleus and is lost more easily.
What are the group 1 alkali metals?
Group 1 sits on the far left of the periodic table. The six elements — lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr) — share a defining feature: every atom has exactly one electron in its outer shell. GCSE chemistry usually focuses on the first three, since rubidium, caesium and francium are rare, expensive, and (in francium's case) intensely radioactive.
Unlike most metals, the alkali metals are soft enough to cut with a knife, have low melting and boiling points that fall as you go down the group, and are far less dense than typical metals — lithium, sodium and potassium are all less dense than water, which is why they float (briefly) before reacting.
Because that single outer electron is held so loosely, alkali metals are never found as free elements in nature. They exist only as compounds — most familiarly, sodium chloride (table salt) — and must be stored under oil, since they react rapidly with oxygen and moisture in the air.
What are the physical properties of alkali metals?
| Property | Detail |
|---|---|
| Appearance (freshly cut) | Shiny, silvery surface that tarnishes rapidly in air |
| Hardness | Soft — can be cut with a knife |
| Density | Low; lithium, sodium and potassium float on water |
| Melting/boiling point | Low compared with other metals; falls down the group |
| Electrical conductivity | Good, like most metals |
| Outer electrons | Exactly 1 (group number = outer electrons) |
The falling melting point is a direct consequence of the same trend that drives reactivity: as atoms get larger down the group, the metallic bonding between atoms weakens slightly, so less energy is needed to break the lattice apart.
How do alkali metals react with water?
Every group 1 metal reacts with cold water to produce a metal hydroxide solution and hydrogen gas. The general word equation is:
alkali metal + water → metal hydroxide + hydrogen
For sodium:
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
Worked example — balancing the potassium equation:
- Start with the skeleton: K + H₂O → KOH + H₂.
- Count atoms on each side: 1 K, 2 H + 1 O (from water) on the left; 1 K, 1 O, 1 H (from KOH) + 2 H (from H₂) on the right — hydrogen doesn't balance yet.
- Double the potassium and water: 2K + 2H₂O → 2KOH + H₂.
- Check: 2 K on both sides, 4 H on both sides (2×2 from water = 4 H; 2×1 from KOH + 2 from H₂ = 4 H), 2 O on both sides. Balanced.
Observable clues you'll be expected to describe in an exam answer:
- Lithium — fizzes steadily, moves across the surface, no flame
- Sodium — melts into a silvery ball from the heat of reaction, fizzes vigorously, may ignite with a yellow-orange flame
- Potassium — reacts violently, ignites almost immediately with a lilac flame, may spit or spark
All three produce an alkaline solution — testing it with universal indicator or litmus turns it purple/blue, confirming the hydroxide product.
Why does reactivity increase down group 1?
This is the single most-asked exam question on this topic, and the answer is entirely about electron structure rather than anything "magical" about individual elements.
Each alkali metal atom has one outer-shell electron that it must lose to form a stable +1 ion (achieving a full outer shell like the nearest noble gas). Reactivity depends on how easily that electron is lost:
- Going down the group, atoms gain an extra electron shell at each step, so the outer electron sits further from the positively charged nucleus.
- Increased distance means weaker electrostatic attraction between the nucleus and the outer electron — this is the dominant effect, even though the nuclear charge is also larger.
- Inner shells of electrons shield the outer electron from the full pull of the nucleus, further reducing the attraction.
- A more weakly held electron is lost more easily, so the atom reacts faster and more energetically.
So the trend is: more shells → outer electron further from the nucleus → weaker attraction → electron lost more easily → higher reactivity. This is why potassium reacts far more violently with water than lithium, even though potassium's nucleus carries a much bigger positive charge.
How does reactivity down group 1 compare with group 7?
Contrast group 1 with group 7 (the halogens): GCSE papers often test whether you can explain both trends with the same shielding-and-distance logic, applied in opposite directions.
| Feature | Group 1 (alkali metals) | Group 7 (halogens) |
|---|---|---|
| Outer electrons | 1 (must be lost) | 7 (one must be gained) |
| Reactivity trend | Increases down the group | Decreases down the group |
| Why | Outer electron further away → lost more easily | Outer shell further away → harder to attract an extra electron |
| Typical reaction | With water/acids, losing an electron | Displacement reactions, gaining an electron |
Group 1 gets more reactive going down because it's easier to lose a distant electron; group 7 gets less reactive going down because it's harder to pull in an extra electron from further away. Same underlying idea — distance from the nucleus — applied to opposite processes.
What happens when alkali metals react with oxygen and chlorine?
Alkali metals also react readily with oxygen in the air, forming a metal oxide and explaining why the shiny cut surface dulls within seconds:
4Li(s) + O₂(g) → 2Li₂O(s)
With chlorine gas, they burn to form white, crystalline metal chloride salts:
2Na(s) + Cl₂(g) → 2NaCl(s)
Reactivity again increases down the group here — potassium burns more vigorously in chlorine than sodium does — for the same electron-shielding reason as the water reactions.
Frequently asked questions
What are the group 1 alkali metals?
The group 1 alkali metals are lithium, sodium, potassium, rubidium, caesium and francium — soft, low-density, shiny metals found in the first column of the periodic table. Each has a single electron in its outer shell, which it loses readily to form a +1 ion. At GCSE, questions focus almost entirely on lithium, sodium and potassium, since the heavier members are rare or dangerously radioactive.
Why does reactivity increase down group 1?
Reactivity increases down group 1 because each element down the group has an extra electron shell, placing the single outer electron further from the positive nucleus. Greater distance and additional inner-shell shielding both weaken the attraction holding that electron in place, so it is lost more easily — and losing that electron more readily is exactly what "more reactive" means for these metals. This is why potassium reacts far more violently with water than lithium does.
What products form when an alkali metal reacts with water?
An alkali metal reacting with water produces a metal hydroxide solution plus hydrogen gas, following the general pattern: alkali metal + water → metal hydroxide + hydrogen. The solution formed is alkaline, turning universal indicator purple or blue. Sodium's reaction with water (2Na + 2H₂O → 2NaOH + H₂) is the version most commonly asked about, but the same pattern applies to lithium and potassium.
Why are alkali metals stored under oil?
Alkali metals are stored under oil to keep them away from oxygen and water vapour in the air, both of which they react with rapidly at room temperature. Left exposed, a freshly cut, shiny surface tarnishes within seconds as it reacts with oxygen to form a dull oxide layer, and moisture in the air can trigger the same vigorous reaction seen with liquid water. Oil forms a physical barrier that excludes both, keeping the metal safe to handle and store.
For Socratic GCSE chemistry tutoring where the particle model comes first and every equation is built from understanding, try Professor Curie at aitutors.me.