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 table.
· The arrangement of electrons in the outermost shell of an elements atom determines the way that element reacts.
· 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 products.
· 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:
· 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.
· Metal carbonates decompose on heating to form the metals oxide and carbon dioxide.
C 2.3. The ‘limestone reaction cycle’:
· When water is added to calcium oxide it produces calcium hydroxide.
· Calcium hydroxide is alkaline so it can be used to neutralize…