The Big Idea
Metals are reactive because they lose electrons easily. The more readily a metal loses electrons, the higher it sits on the reactivity series. This explains how metals react with water and acid, why iron rusts (needing both oxygen AND water), and how we can protect metals from corrosion using barrier methods or sacrificial protection.
- The reactivity series orders metals by how easily they lose electrons
- Rusting requires both oxygen and water — never just one
- More reactive metals displace less reactive metals from salt solutions
- Sacrificial protection & galvanising are two distinct anti-corrosion methods
The Reactivity Series
What is the Reactivity Series?
The reactivity series is a list of metals (and two non-metals) arranged in order of how readily they lose electrons when they react with other substances. It's essentially a ranking of "how keen each metal is to react."
The Reactivity Series (from most to least reactive)
Potassium → Sodium → Calcium → Magnesium → Aluminium → Carbon → Zinc → Iron → Hydrogen → Copper → Silver → Gold
Notice that carbon and hydrogen are included (they're non-metals), because they're used to extract metals from their oxides in industry. The mnemonic is:
Memory Aid
"Please Send Cats, Monkeys And Cute Zebras Into Hot Countries Signed Gordon"
P-S-C-M-A-C-Z-I-H-C-S-G = each first letter = each metal/non-metal in order.
Why This Order?
Metals at the top of the series lose electrons very easily, so they react vigorously. Metals at the bottom lose electrons reluctantly, so they barely react at all. The "strength" of a metal's desire to lose electrons determines its position on this list.
Metals Reacting with Cold Water
Only the most reactive metals (potassium, sodium, and calcium) react with cold water. All three form a metal hydroxide and hydrogen gas:
metal + water → metal hydroxide + hydrogen gas
Potassium (K)
Reacts violently with cold water — the reaction is so vigorous it often ignites the hydrogen gas.
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)
Sodium (Na)
Reacts quickly with cold water — slower than potassium but still energetic.
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
Calcium (Ca)
Reacts less strongly with cold water — noticeably slower than sodium.
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
Exam Tip
When describing these reactions, use words like "vigorous," "rapidly," or "slowly" to show you understand the difference in reactivity. Don't just say "they react" — show you can observe and interpret the difference in reaction rates.
Metals Reacting with Steam
Magnesium doesn't react much with cold water, but it does react with steam. It forms a metal oxide (not a hydroxide) and hydrogen gas:
Mg(s) + H₂O(g) → MgO(s) + H₂(g)
This is an important distinction: with cold water, you get hydroxides; with steam, you get oxides.
Metals Reacting with Dilute Hydrochloric Acid
All metals above hydrogen in the reactivity series will react with dilute HCl to produce a salt and hydrogen gas. Those below hydrogen (copper, silver, gold) don't react at all.
metal + dilute HCl → salt + hydrogen gas
Metals That React (Above Hydrogen)
- Magnesium: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
- Zinc: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
- Iron:
Rusting of Iron