Atoms, elements and compounds
- All substances are made up of atoms.
- 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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