If a substance is only made up of one type of atom, we call it an element.
There are around 100 elements, all shown in the periodic table.
Each group of the periodic table contains elements with similar properties.
Elements are represented by symbols.
Atoms have a small central nucleus, made up of protons and neutrons, which is surrounded by electrons.
Compounds are made up of two or more types of atom which have reacted together.
Atoms react to form compounds by giving, taking or sharing electrons.
Atoms in compounds are held together by chemical bonds.
No atoms are made or lost in a reaction so the mass of the products is the same as the mass of the reactants. This is why symbol equations must be balanced.
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Limestone and its products 1
Limestone is mostly made of calcium carbonate (CaCO3)
Limestone can be quarried and used as a building material
Thermal decomposition is breaking down using heat
Calcium carbonate can be decomposed by heating to make quicklime, which is also known as calcium oxide (CaO), and to make carbon dioxide (CO2)
Carbonates of other metals can be decomposed in a similar way
Quicklime is reacted with water to produce slaked lime - calcium hydroxide (Ca(OH)2)
Quicklime can be made in a furnace called a lime kiln
Slaked lime, mortar, cement, concrete and glass all come from limestone
We can dissolve slaked lime in water and filter to get lime water
Slaked lime is reacted with carbon dioxide to get limestone and water
Mixing slaked lime with sand and water gives us mortar, which is used as a building material
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Limestone and its products 2
Heating limestone with clay in a kiln produces cement
Portland cement is made from a mixture of limestone, clay and other minerals which are heated and ground into a fine powder
Modern houses are made from a mixture of Portland cement and sand, which sets when it is mixed thoroughly with water and left for a few days
A mixture of water, cement and sand has stones or crushed rocks added to it to form concrete when it sets.
Concrete can be made even stronger by pouring it around steel rods or bars and leaving it to set. This is reinforced concrete.
Glass is made when powdered limestone is mixed with sand and sodium carbonate and heated strongly
Glass allows us to make buildings both weatherproof and light.
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