Reactivity Series

Some metals are more reactive than other metals. As a result, we can put the metals in a list in order of their reactivity. We call this list the reactivity series of metals. In this article, you will learn what this reactivity series looks like, how we work out what metals are more reactive than others, and when you will use this list.

Reactivity series: definition

The reactivity series is a list of metals ordered from most reactive to least reactive. Sometimes, it is called an activity series, especially if you are looking at American sources. You will often find the reactivity series with carbon and hydrogen, even though the two are not metals.

The reactivity series is:

Make sure you memorise this list by heart!

Of course memorising the whole list just by looking at it can seem really daunting, so it is useful to have a mnemonic to help you. Here’s one but of course, feel free to make up your own!

Police Sergeant Charlie MA(C)ZITL Has been Caught Stealing gold Plates.

Here is another one - Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold and Platinum.

Memonics don't have to make sense, they just have to be fun. You will remember a memonic for a lot longer than you would remember a boring sequence of elements! Each letter in bold in these memonics corresponds to an element in the reactivity series.

From the reactivity series, you can see that potassium is the most reactive metal, and the least reactive is platinum. Phosphorous and sodium burns instantaneously when in contact with air. You will get a chance to see this in action in the chemistry lab. Then at the bottom of the list there is gold, silver and platinum. They are so unreactive that they are deemed safe for use in jewellery. For a substance to be used as jewellery it has to be very inert as you do not want it to react with your skin for the entirety of its life!

How do we work out the order of the reactivity series?

To work out the order of the reactivity series, we obviously need to find out if one metal is more reactive than another metal. Reactivity is all about electrons. For metals, the reactivity of a metal depends on how easily it loses electrons. If it loses electrons really easily, it is really reactive, and so goes at the top of the reactivity series. Potasium and sodium lose electrons very easily. On the other hand, it is really hard for a metal like platinum to lose its electrons, so it is not reactive, so goes at the bottom.

In practice, we can work out reactivity by observing how a substance reacts with diifferent metals. We can see if the metal reacts with the substance instantly, if it reacts when more energy is added (e.g. heat), or if it does not react with the substance at all under any circumstance.

Let us see this in more detail, with two substances - water and acid - for better understanding.

Reacting with water

We can compare how vigorously metals react with water. For example, alkali metals react very vigorously with water, whilst most other metals e.g. copper, do not react at all. When metals react with water, they produce a salt and hydrogen gas. The hydrogen gas appears as fiz. The fizzing is how we know if a metal has reacted or not.

$$ Metal + Water \rightarrow Salt + H_{2(g)} $$

Fig. 1;: Calcium reacting with water | Mammoth Memory

We know that reactivity increases as you go down group 1, so we can already order the alkali metals in order of reactivity:

1. Potassium.
2. Sodium.
3. Lithium.

We can also put all the other metals below them, as they do not react with water at all, so they must be less reactive.

There are some elements that take a long time to react or do react with water spontaneously and need to be heated. One example is magnesium, which reacts with water only when left in a beaker filled with water for several days. Therefore, we know that we can place elements that react like this between alkali metals (which react vigorously), and most transition metals (which do not react at all).

Reacting with acid

Reacting with water is very useful, but for some metals, this reaction is very, very slow. In these cases, we can see how metals react with acid. Reacting with acid tends to be faster and more vigorous than reacting with water.

Like with water, when metals react with acid, they produce a salt and hydrogen gas. The hydrogen gas appears as fizzing. The fizzing is how we know if a metal has reacted or not.

$$ Metal + dil. Acid \rightarrow Salt + H_{2(g)} $$

The most reactive elements, such as potassium and sodium, will explode when they are reacted with dilute acid.

The fairly reactive elements, such as magnesium and aluminium, fizz and give off hydrogen gas when they react with dilute acid. The least reactive elements, such as silver and gold, still do not react even with acid.

Fig. 2: Potassium, magnesium, and zinc reacting with a dilute acid | The Science Hive

Here is a table that shows the observations of the reactions between each element and water, and each element with acid.

You can see that the more reactive the elements are, the more vigorously they react.As they decrease in reactivity, the reactions become less vigorous.

When do we use the reactivity series?

The reactivity series is really useful for a number of situations.

One way is we use it to predict the outcome of displacement reactions, where a more reactive metal will displace a less reactive metal in a compound. If you want to learn more, head over Displacement reactions!

We can also use the reactivity series with hydrogen and carbon, to extract these metals from their ores. You can read more about it in Extracting Metals.