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Summary Complete grade 9 AQA GCSE Chemistry notes
very detailed chemistry notes tailored for AQA GCSE Chemistry that got me a grade 9
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1 Atomic structure and the periodic table1.1 A simple model of the atom, symbols, relative atomic mass, electronic charge and
isotopes
1.1.1 Atoms, elements and compounds
------ Atom
Tiny particles of matter that makes all substances
Radius = 0.1 nanometers
✪ Consists of the following subatomic particles:
Protons – located at centre of atom
Neutrons – located at centre of atom (nucleus)
Electrons – on the energy levels/shells
Remember:
* relative atomic mass – average mass of its atom compared to 1/12th the mass of a carbon-
12 atom
✪ Chemical symbols
Atoms of each element are represented by a chemical symbol
e.g. O = atom of oxygen; Na = atom of sodium
Element = made of one type of atom
Around 100 different elements, shown in the periodic table
, 12 = mass number
6= atomic number = proton no = electron no
12-6=6 = neutron number
✪ Isotopes
Elements with same number of protons but different number of neutrons
------ to calculate relative atomic mass
✪ Compounds
Made up of 2 or more types of atom
Chemically bonded
e.g. carbon dioxide, aspirin, water
* molecules = compounds formed from only non-metals consists of particles
1.1.2 Mixtures
✪ Contain two or more elements or compounds
Easily separated as there are no chemical bond between different parts
Can be separated by:
- Filtration
Separate undissolved solid from mixture of solid and liquid e.g. separating sand
- Crystallisation
Separating soluble solid e.g. copper sulfate
Put into evaporating basin, warm it up until all liquid leaves
- Simple distillation
,2 liquids mixed together
Heat up until 1 turns to gas after evaporated, cool down, condenses back to being a liquid
- Fractional distillation
Mixture of more than 2 liquids
Fractionating column w temp gradient
Reach boiling point and condenses as liquids
Chromatography
Analytical technique
1.1.3 The development of the model of the atom
Tiny spheres – Dalton though that atoms were tiny spheres and could not be divided
Discovery of electron by J J Thomson
Plum pudding model – proposed by J J Thomson
Positive ‘dough’ with negative electrons embedded
Alpha scattering experiment – performed by Rutherford
Firing a beam of alpha particle at thin gold foil
According to plum pudding model particles would pass straight through, or slightly deflected
In reality, some were deflected by large angles e.g.
completely bouncing back
Conclusions:
Mostly empty space as most alpha particles went through
Nucleus of atom has strong positive charge as the positive alpha particles were repelled by
positive charges and only a few were deflected
Most of the mass is concentrated at the centre as a few alpha particles rebounded
, Discovery of proton by Rutherford
Rutherford proposed the nuclear model:
Positive charged nucleus surrounded by negative electrons
Bohr discovered the energy levels, said that electrons orbit the nucleus at certain distance
Discovery of neutron by James Chadwick which explained isotopes
✪ Plum pudding model vs nuclear model
Plum pudding model Nuclear model
Mass is evenly distributed Mass concentrated at the centre
(nucleus)
Positive charge spread throughout Positive charge occupies only a
the atom small part of atom
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