Metal reactivity: the more readily a metal forms positive ions, the more reactive it is

1. When a metal reacts, its atoms lose electrons and form positive ions.
2. A metal is more reactive if its atoms form positive ions more readily.
3. Under the same conditions, a more reactive metal reacts faster and more vigorously than a less reactive one.
4. A reactivity series lists metals in order of how readily they react.

The order: potassium is the most reactive and copper the least

1. The metals and the two non-metal reference points are listed from the most reactive at the top to the least reactive at the bottom.
   1. Potassium (K), the most reactive.
   2. Sodium (Na).
   3. Lithium (Li).
   4. Calcium (Ca).
   5. Magnesium (Mg).
   6. Carbon (C), a non-metal reference point.
   7. Zinc (Zn).
   8. Iron (Fe).
   9. Hydrogen (H), a non-metal reference point.
   10. Copper (Cu), the least reactive.
2. Carbon and hydrogen are non-metals, included only as useful reference points.
3. This order is based on reactions at room temperature and does not include reactions with steam.

Reactions with water: vigour falls as you go down the series

1. A metal that reacts with room-temperature water forms a metal hydroxide and hydrogen.
2. $$metal+water\to metal\; hydroxide+hydrogen$$
3. Potassium reacts most vigorously: it melts, moves rapidly and ignites with a lilac flame.
4. Sodium melts into a ball, fizzes and darts across the surface, sometimes igniting with an orange flame.
5. Lithium floats and fizzes steadily, moving more slowly than sodium.
6. Calcium sinks and fizzes, and the water may turn cloudy because calcium hydroxide is only slightly soluble.
7. Magnesium reacts extremely slowly, giving only a few bubbles.
8. Zinc, iron and copper show no reaction with room-temperature water.

Reactions with dilute acids: hydrogen separates the reactive metals from copper

1. A metal that reacts with a dilute acid forms a salt and hydrogen.
2. $$metal+acid\to salt+hydrogen$$
3. Metals above hydrogen in the series react with dilute acids; metals below hydrogen do not.
4. Magnesium reacts rapidly with strong fizzing, zinc steadily, and iron slowly.
5. Copper does not react because it sits below hydrogen.
6. Potassium and sodium react dangerously with acid, so they are not used in a school comparison.
7. For example, magnesium and hydrochloric acid: $$Mg(s)+2HCl(aq)\to {MgCl}_2(aq)+H_2(g)$$

Displacement: a more reactive metal takes a less reactive metal's place

1. A displacement reaction happens when a more reactive metal replaces a less reactive metal in a compound.
2. If metal A displaces metal B from its compound, then A is more reactive than B.
3. If A does not displace B under suitable conditions, then A is less reactive than B.
4. Zinc added to blue copper sulfate solution coats itself in reddish-brown copper and the solution fades.
5. $$Zn(s)+{CuSO}_4(aq)\to {ZnSO}_4(aq)+Cu(s)$$
6. Copper does not displace zinc from zinc sulfate, because copper is the less reactive metal.

Building the order from experimental evidence

1. When comparing acids, keep the metal mass, surface area, the acid volume, concentration and the temperature the same.
2. A more reactive metal gives faster fizzing, more hydrogen in a fixed time, or the same volume of hydrogen sooner.
3. Each successful displacement shows the added metal is more reactive than the one in the compound.
4. Putting the results together gives the order magnesium, zinc, iron, hydrogen, copper.