Key points
- Metals mostly occur as compounds in rocks and minerals and must be extracted before they can be used.
- The method used to extract the pure metal depends on its position in the reactivity series.
In which area of the periodic table are metals found?
Metals are found on the left and the middle of the periodic table.
Metals make up most of the elements in the periodic table and are found to the left of a stepped line beginning below boron (B).
Metals in the Earth
Metals are very important materials in our everyday lives. There is a high demand for metals to be used in many kinds of industries.
Metals are found in rocks in the Earth鈥檚 crustThe Earth鈥檚 crust is the rocky outer layer of the Earth. which must be processed to get the pureA substance of only one element or one compound. metal. This is called extraction and can involve several different steps, including chemical reactionWhen chemical bonds are broken and made between atoms, so that new substances (compounds or elements) are made..
Unreactive metals
The most unreactiveA substance that does not readily undergo chemical reactions. metals, silver and gold, are found as elementA pure substance which is made from only one type of atom. Elements are listed on the periodic table. in the rocks. They are not chemical bondThe force that holds ions, atoms or molecules in a chemical compound. to other elements in compounds.
For example, gold (element symbol Au) is an unreactive metal and is found as an element in rocks.
Metals in compounds
Most of the metals found in rocks are combined with other elements in compoundA pure substance made from two or more elements which are chemically bonded in a fixed ratio. . These compounds are called mineralA solid compound which occurs naturally in rocks..
For example, iron (element symbol Fe) is mostly found as the minerals magnetite Fe鈧僌鈧 and hematite Fe鈧侽鈧. Both are compounds of iron chemically bonded to oxygen.
Copper is more reactiveThe tendency of a substance to undergo a chemical reaction. than gold and so is found in rocks as a compound. This image of a green rock contains malachite, a compound of copper, carbon and oxygen.
Did you know?
Minerals can have really complicated formulas.
For example, the rare red mineral eudialyte has a simplified formula of 狈补鈧佲倕颁补鈧咶别鈧僊苍鈧僙谤鈧侨颈鈧傗倕翱鈧堚倓贬鈧圕濒鈧.
That is nine different elements and over 100 atomThe smallest particle of an element. We often think of atoms as tiny spheres, but in fact they are made from smaller particles called protons, neutrons and electrons. in each formula unit.
How are precious metals like gold and silver found in rocks?
As pure elements rather than chemically bonded to other elements in compounds.
This is because gold and silver are unreactive metals so they are not found chemically bonded to other elements.
Methods of extracting metals
Different methods are used to extract a metal depending on its position in the reactivity series.
The diagram shows a simple reactivity series, including carbon and hydrogen. Carbon and hydrogen are often included in a reactivity series as they allow us to predict particular chemical reactions.
The reactivity series can be split up to show how metals are extracted into three groups:
Metals which are found in the pure crust.
Reduction of metal oxides using carbon.
Extraction using electrolysis.
1. Metals which are found pure in the crust
Metals with very low reactivity can be found as elements in rocks, such as silver and gold.
The metal is visible running through the rock. They do not need to be treated using a chemical reaction for the pureA substance of only one element or one compound. metal to be obtained.
To extract the metal from the rock, the rock is crushed and the metal is then melted out
2. Reduction of metal oxides using carbon
Zinc, iron and copper are all found as compounds within rocks. They are generally found bonded to oxygen as compoundA pure substance made from two or more elements which are chemically bonded in a fixed ratio. called metal oxideA compound which contains an element bonded to oxygen. .
These metals are extracted using carbon in a displacement reactionA reaction where a more reactive element displaces a less reactive element from its compound.. This is because carbon is cheap and readily available.
The reactantThe chemical present at the start of a reaction. Reactants appear on the left of a chemical equation, before the arrow 鈫. are the metal oxide compound and carbon. The productA chemical which is made in a chemical reaction. Products are written on the right of a chemical equation, after the arrow (鈫). are the pure metal and either carbon monoxide or carbon dioxide.
For example:
metal oxide + carbon 鈫 metal + carbon oxide
Carbon is more reactive than zinc, iron and copper. This means the carbon takes the oxygen away and displaceWhen an element is displaced, it is pushed out of a compound by a more reactive element. the metal. This leaves the metal as a pure elementA pure substance that is made from only one type of atom. Elements are listed on the periodic table. Elements cannot be broken down into simpler substances. .
The carbon makes an oxide - either carbon monoxide (CO) or carbon dioxide (CO鈧).
This is a specific type of displacement reaction. The more reactive element (carbon) is displacing the less reactive element (in this case a metal) from its compound.
A chemical reaction where oxygen is removed from a compound is called a reductionA reaction involving the loss of oxygen from an element.. This method is called reduction with carbon.
These reactions can be described using either word or symbolchemical equationA way of describing chemical reactions in words or symbols..
For example, the word equation for the reduction of zinc oxide with carbon is:
zinc oxide + carbon 鈫 zinc + carbon monoxide
The symbol equation for the reduction of zinc oxide with carbon is:
ZnO + C 鈫 Zn + CO
3. Extraction using electrolysis
When metals are above carbon in the reactivity series, they cannot be extracted using reduction with carbon. Carbon is not reactive enough to take the oxygen away from the metal.
These metals are extracted using a process called electrolysisSplitting up a liquid or dissolved compound into its elements using electricity. . In electrolysis, an electric current is passed through the compound to split up the metal and the oxygen. In industry, this is carried out on a large scale, but a small scale experiment can be carried out using a power pack to provide the electricity.
For example, an electric current can be passed through aluminium oxide (the compound) to split up the metal (aluminium) and the oxygen.
Why can carbon not be used to extract potassium?
Carbon is below potassium in the reactivity series.
This means carbon is not reactive enough to displace potassium from its compound.
Working scientifically
Making predictions
Not all metals in the periodic tableA table which lists all of the chemical elements and arranges them in a way that is useful. It allows us to spot patterns and make predictions about other elements. are shown in a simple reactivity series. We can use information about their place in an expanded reactivity series to predict the method of extraction.
For example, platinum is a less reactive metal than gold. Gold is found as an element, so we can predict that platinum will also be found as an elementA pure substance which is made from only one type of atom. Elements are listed on the periodic table. and won鈥檛 need a chemical reaction to extract it.
Use the simple reactivity series to make predictions for the following questions.
1. Tin is more reactive than copper, but less reactive than iron. Both copper and iron are found as compounds in rocks and are extracted using reduction with carbon.
What extraction method can we predict would be used for tin?
Tin sits between copper and iron in the reactivity series. We can therefore predict that tin will also be extracted using reduction with carbon.
Cans which are used to store food are often called 鈥榯in cans鈥 because the original cans made in the early 1800s were made from tin. Nowadays, food cans are mostly made from steel, coated on the inside with plastic (or very occasionally a thin layer of tin).
Cans used for drinks are usually made from aluminium.
2. Strontium is more reactive than calcium but less reactive than potassium. Both calcium and potassium are extracted using electrolysis.
What extraction method would be used for strontium?
As strontium sits between calcium and potassium in the reactivity series, we can predict that strontium will also be extracted using electrolysis.
Strontium is named after the small Scottish village of Strontian, which is where rocks containing strontium were first discovered.
3. Lead is more reactive than copper, but less reactive than iron.
What extraction method would be predicted for lead?
We can predict lead would be extracted using reduction with carbon.
This is because we know from the reactivity series that both copper and iron also use reduction with carbon.
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