Not all metals react with equal intensity. Some, like potassium, are so reactive that they must be stored under oil to prevent them from reacting with the air, while others, like gold, are so stable that they remain shiny and unchanged for thousands of years. The Reactivity Series is a list of elements (primarily metals) arranged in order of their chemical reactivity. Understanding this sequence allows chemists to predict which displacement reactions will occur and which methods are necessary to extract metals from their ores. The IGCSE 0654 Core syllabus requires students to recall the order of the series and describe the specific reactions of metals with water, steam, and acids.

The elements are arranged from the most reactive at the top to the least reactive at the bottom. Note that Carbon and Hydrogen are included as non-metal reference points, which is critical for understanding metal extraction and acid reactions.

1. Potassium ($K$) - Most Reactive
2. Sodium ($Na$)
3. Calcium ($Ca$)
4. Magnesium ($Mg$)
5. Aluminium ($Al$)
6. Carbon ($C$)
7. Zinc ($Zn$)
8. Iron ($Fe$)
9. Hydrogen ($H$)
10. Copper ($Cu$)
11. Silver ($Ag$)
12. Gold ($Au$) - Least Reactive

The position of a metal in the series determines how it will react with common laboratory reagents.

(a) Reactions with Cold Water

Only the most reactive metals (the top three) react significantly with cold water.

• Equation: Metal + Water $\rightarrow$ Metal Hydroxide + Hydrogen
• Metals: K, Na, and Ca react vigorously. Bubbles of hydrogen are seen, and the resulting solution is alkaline.

(b) Reaction with Steam

Magnesium is unique in that it reacts very slowly with cold water but reacts vigorously when heated in steam.

• Equation: Magnesium + Steam $\rightarrow$ Magnesium Oxide + Hydrogen
• Observation: A white light is often produced as the magnesium burns in the steam.

(c) Reactions with Dilute Hydrochloric Acid

Metals above hydrogen in the series will displace hydrogen from an acid.

• Equation: Metal + Acid $\rightarrow$ Salt + Hydrogen
• Metals: Mg, Zn, and Fe react with increasing slowness. Magnesium fizzes rapidly, while iron fizzes slowly.
• The Bottom Three: Cu, Ag, and Au are below hydrogen in the series. They are not reactive enough to displace hydrogen ions from the acid. Therefore, no reaction occurs when these metals are placed in dilute $HCl$.

A critical scientific skill is the ability to deduce the reactivity of an unknown metal based on experimental observations.

• If Metal X reacts with cold water but Metal Y only reacts with acid, then Metal X is more reactive than Metal Y.
• If Metal Z does not react with acid at all, it must be below hydrogen in the series.

The Reactivity Series is the blueprint for predicting chemical behavior in inorganic chemistry. By mastering the order and the associated reaction patterns with water and acids, chemists can select materials for specific environments and develop the industrial processes necessary to extract metals from the earth.