AQA GCSE Chemistry Unit 1

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…