The metal reactivity series is a commonly taught concept in chemistry, placing the metals, as its name suggests, in order of reactivity from most reactive to least reactive. It’s also a useful tool in predicting the products of simple displacement reactions involving two different metals, as well as providing an insight into why different metals are extracted from their ores in different manners. This graphic places a selection of common metals into order of reactivity, as well as showing their reactions with air, water and steam.
Metals have a range of reactivities – to illustrate this, you have to look no further than the classic alkali metals in water demonstration commonly used in chemistry classes. In this demonstration, small pieces of three different metals from group 1 of the periodic table are dropped into a large bowl of water. Lithium fizzes gently, sodium fizzes vigorously, and potassium’s reaction is so energetic it bursts into a lilac flame as it zips across the water’s surface. Caesium, the most reactive metal in the periodic table, reacts extremely violently – hence why it can’t be demonstrated in a classroom! This can be compared to other common metals, such as iron and copper, which produce no reaction when dropped into water.
The reactivity series offers a ranking of the metals in order of their reactivity. Group 1 metals, the most reactive metals in the periodic table, head up the rankings. They’re closely followed by the marginally less reactive group two metals. The metals designated as the transition metals in the periodic table are much less reactive, and metals such as gold and platinum prop up the bottom of the series, exhibiting little in the way of chemical reaction with any everyday reagents.
What use does this series have beyond ranking the reactivity of metals, though? Well, for one, it can help us predict the outcome of certain chemical reactions. If a metal compound reacts with a metal that’s above it in the reactivity series, a displacement reaction will occur, and the more reactive metal will take the place of the less reactive metal in the compound. Conversely, if we try and react a metal compound with a metal lower in the reactivity series, no reaction will take place. This is illustrated below:
Copper sulfate + zinc → zinc sulfate + copper
Magnesium sulfate + zinc → NO REACTION
As well as helping us predict the outcomes of these reactions, the reactivity series also gives us an insight into why different metals are extracted from their ores in different ways. You’ll notice in the graphic that carbon and hydrogen are also shoehorned in between entries in the list, despite being non-metals. This is because they can react with the compounds in metal ores, and displace the metals, aiding with their extraction. Some metals, such as gold and silver, are so unreactive they occur largely uncombined with other elements, and are relatively simple to obtain. However, the majority of metals will occur naturally in compounds, often in combination with oxygen or sulfur, which we must remove them from.
The extraction method used for many metals is the blast furnace process, in which the metal ore is heated with carbon. This is a case with a common example, iron, the ore of which, haematite, consists primarily of iron oxide. The carbon burns in the furnace to form carbon monoxide; carbon monoxide then reacts with the iron oxide, displacing the iron and forming carbon dioxide. This extraction is possible because iron is below carbon in the reactivity series, and works similarly well for other metals below carbon. However, with some metals, metal-carbon carbide compounds are formed, which can cause the metal to be brittle. For this reason, other extraction methods are sometimes necessary. As well as this, it’s impossible to use carbon to extract metals that are more reactive than carbon in the reactivity series.
For those metals that could be extracted with carbon, but form carbides, a range of different extraction methods can be used. Titanium has a high strength to weight ratio, and has important uses in the aerospace industry. It’s extracted from its ore, rutile, which is primarily titanium dioxide, using chlorine and carbon, which converts the titanium dioxide to titanium tetrachloride. This can then be reacted with a more reactive metal, such as sodium or magnesium, to produce titanium.
Another metal, tungsten, forms a carbide which can actually be of use, as it is extremely hard. On the Moh’s scale of mineral hardness, which ranks substances from 1 to 10, it scores a 9; equal to the hardness of rubies, and bested by only a few substances. For reference, diamond comes in at a 10 on the Moh’s scale. Tungsten carbide finds use in drill bits as a result of its hardness. To extract tungsten from its ore without forming the carbide, hydrogen is reacted with tungsten oxide at a high temperature, displacing the metal.
For the metals highest in the reactivity series, extraction using carbon simply isn’t a possibility. Instead, a different method altogether is used. This method, electrolysis, involves passing an electric current through the molten metal ore. This decomposes the ore, splitting it into its component elements, and allowing the metal to be extracted. Whilst this method has to be used for metals such as aluminium, it’s also an expensive one, with the associated electrical energy costs being high.
This graphic, by necessity, doesn’t contain every metal in the periodic table, which would require much more space (perhaps an idea for a future project!). There are also some caveats to the reaction statements; for example, aluminium will react slowly with water if the thin aluminium oxide layer that prevents it from reacting is damaged. However, despite this, hopefully it still functions as a well-rounded introduction to the reactivity series and some reactions that can be used to evidence it.
You can download the PDF of this graphic below; there’s also a blank version for teaching here.
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References & Further Reading
- Extraction of Metals – ChemGuide
- The Reactivity Series – Universe Review
- Element images via images-of-elements.com & Wikimedia Commons user Dnn87