GCSE Chemistry Unit 1 Key Points

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AQA GCSE Chemistry Unit 1
C 1: Fundamental ideas:
C 1.1. Atoms, elements and compounds:
All substances are made up of atoms.
Elements contain only one atom.
Compounds contain more than one atom.
An atom has a tiny nucleus in its centre, surrounded by electrons.
C 1.2. Atomic structure:
Atoms are made up of protons, neutrons and electrons.
Protons and electrons have equal and opposite electrical charges. Protons are positively charged, and electrons
are negatively charged.
Neutrons have no electrical charge. They are neutral.
Atomic number = number of protons (number of electrons.)
Mass number = number of protons and neutrons.
Atoms are arranged in the periodic table in order of their atomic number.
C 1.3. The arrangement of electrons in atoms:
The electrons in an atom are arranges in energy levels or shells.
Atoms with the same number of electrons in their outermost shell belong in the same group of the periodic
The arrangement of electrons in the outermost shell of an elements atom determines the way that element
The atoms of the unreactive noble gases (in group 0) all have very stable arrangements of electrons.
C 1.4. Forming bonds:
When atoms from different elements react together they make compounds. The formula of a compound shows
the number and type of atoms that have bonded together to make that compound.
When metals react with non-metals, charged particles called ions are formed.
Metal atoms form positively charged atoms. Non-metals form negatively charged atoms. These oppositely
charged ions attract each other in ionic bonding.
Atoms of non-metals bond to each other by sharing electrons. This is called covalent bonding.
C 1.5. Chemical equations:
As no new atoms are ever created or destroyed in a chemical reaction: total mass of reactants = total mass of
There is the same number of each type of atom in each side of a balanced symbol equation.
C 2: Rocks and building materials:
C 2.1. Limestone and its uses:

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Limestone is made mainly of calcium carbonate.
Limestone is widely used in the building industry.
The calcium carbonate in limestone breaks down when we heat it strongly to make calcium oxide and carbon
dioxide. The reaction is called thermal decomposition.
C 2.2. Reaction of carbonates:
Carbonates react with dilute acid to form a salt, water and carbon dioxide.
Limewater turns cloudy in the test for carbon dioxide gas. A precipitate of insoluble calcium carbonate causes the
cloudiness.…read more

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Stainless steels, which are resistant to corrosion.
C 3.3. Aluminum and titanium:
Aluminum and titanium are useful because they are resistant to corrosion.
Aluminum requires the electrolysis of molten aluminum oxide to extract it as it is too reactive to reduce it using
Aluminum and titanium are expensive because extracting them from their ores involves many stages and
requires large amounts of energy.
C 3.4.…read more

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Sulfur impurities in fuels burn to form sulfur dioxide which can cause acid rain.
Changing the conditions in which we burn hydrocarbon fuels can change the products made.
In insufficient oxygen we get poisonous carbon monoxide gas formed. We can also get particulates of carbon
(soot) and unburnt hydrocarbon s especially if the fuel is diesel.
At high temperatures in engines, nitrogen from the air reacts with oxygen to form nitrogen oxides. These cause
breathing problems and can cause acid rain.
C 4.4.…read more

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C 5.4. Plastic waste:
Non-biodegradable plastics cause unsightly rubbish, can harm wildlife and take up space in landfill sites.
Biodegradable plastics are decomposed by the action of microorganisms in soil. Making plastics with starch
granules in their structure help the microorganisms break down a plastic.
We can make biodegradable plastics from plant material such as cornstarch.
C 5.5. Ethanol:
Ethanol can be made from ethane reacting with steam in the presence of a catalyst. This is called hydration.…read more

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C 7: Our changing planet:
C 7.1. Structure of the earth:
The earth consists of a series of layers. Starting from the surface we have the crust, the mantle then the core in
the centre. A thin layer of gases called the atmosphere surrounds the earth.
The earths limited resources come from the crust, the oceans, and the atmosphere.
C 7.2. The restless earth:
The earth's crust and upper mantle is cracked into a number of massive pieces (tectonic plates) which are
constantly moving slowly.…read more

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