The reactivity series

You can rank metals by how desperate they are to react. That ranking is called the reactivity series. reactivity series: When you line metals up from the ones that react most easily to the ones that barely react at all, you get the reactivity series.

You build this order from what you actually see in reactions, not by guessing. If your metal reacts fast with water, acids or oxygen, it belongs higher up. If your metal needs strong heating or does almost nothing, it belongs lower down.

A useful version of the series includes carbon and hydrogen as reference points as well as metals. In a simplified order, you can think of it like this: potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold, platinum.

One weird thing you should remember: gold is valuable partly because it is chemically lazy. It stays shiny because it resists reacting with oxygen, so it does not tarnish easily like more reactive metals do.

You can learn a lot just by seeing how your metal behaves with water. The metals near the top of the series, such as potassium, sodium, lithium and calcium, react with cold water strongly enough to fizz, heat up and sometimes set the hydrogen on fire.

For Group 1 metals, the pattern is:

$2\mathrm{M}(\mathrm{s})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\to 2\mathrm{MOH}(\mathrm{aq})+{\mathrm{H}}_2(\mathrm{g})$

Your products are hydrogen gas and a metal hydroxide in solution. metal hydroxide: A metal hydroxide is a compound made when a metal joins with hydroxide ions, and many of these dissolve to give an alkaline solution.

Metals in the middle, like magnesium, zinc and iron, usually show little or no change with cold water. Give them steam instead, and they react to make a metal oxide plus hydrogen.

One example is:

$\mathrm{Mg}(\mathrm{s})+{\mathrm{H}}_2\mathrm{O}(\mathrm{g})\to \mathrm{MgO}(\mathrm{s})+{\mathrm{H}}_2(\mathrm{g})$

At the low-reactivity end, copper, silver and gold do not react with water or steam. So if your unknown metal reacts violently with cold water, you already know it must be placed high in the series.