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Grade 9: GCSE EdExcel Chemistry Notes + Summary on ALL topics
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Revision outline for all topics of triple science edexcel GCSE Chemistry, used alongside past papers to secure a grade 9.
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Chemistry(SC1-2) SC1-States of Matter & SC2-Methods of Separating and Purifying
Substances
(Paper 1)
SC1
Arrangement of particles : Random, far apart Random, close together Regular, close together
Movement: Fast in all directions Move around each other Vibrate about fixed positions
State changes are physical changes that can be reversed and do not
affect the chemical properties, as the only change is in the
arrangement and amount of stored energy.
Below the melting point the substance is solid
Between the melting point and boiling point, the substance is liquid
Above the boiling point the substance is gas
SC2
SC2a mixtures
The composition of a pure substance cannot be changed and is constant in all areas. Both elements and compounds
can also be pure. Mixtures contain elements and/or compounds that are not chemically joined together, and can thus
be separated via physical processes. They do not have a fixed composition. Mixed substances have sharp and fixed
melting points unlike pure substances, these are curved and the whole thing melts/boils at the same time
SC2b filtration and crystallisation
Filters let smaller pieces and liquids in, but trap bigger pieces/insoluble
substances.
Solutions are mixtures made of solutes (dissolved substances) in a liquid
called the solvent. Crystallisation is where the solvent is evaporated to
leave the solutes behind. A saturated solution is a solution that contains
the maximum amount of solute that can dissolve in the solvent at that
temperature. If the solution cools/water evaporates then solute leaves the solution and
crystals form.
A hazard is something that could cause harm. During crystallisation, one should wear eye protection, remove the
Bunsen burner before the solution completely dries and use steam to heat the evaporating basin gently.
SC2c paper chromatography
Chromatography is used to find out which coloured compounds the mixture contains. The mobile phase is the
solvent. The paper contains the stationary phase. The paper with the separated components on it is the
chromatogram. The Rf value is distance moved by spot/solvent . It stays the same for a particular compound
assuming conditions stay the same. Paper chromatography can be used to distinguish between pure and impure
substances, identify substances by calculating their Rf values, or identify substances by comparing the pattern on the
chromatogram with the patterns formed by known substances.
,SC2d distillation
Used to separate a solution from its solutes; separate water from dissolved solutes to get pure water. The solution is
evaporated, turning the water to a gas, leaving behind the solid minerals. the water vapour will be pure, and if
condensed, will turn back to pure liquid water. The apparatus used is called a still.
Fractional distillation is where one separates 2 or more liquids: as some liquids will boil more easily. these will turn
into a vapour first. It is fractional distillation because the first fraction to be collected contains the liquid with the
lowest boiling points. it is used to: separate different products in crude oil, make alcoholic drinks (like whisky/vodka),
to separate gases in the air after it has been cooled and turned into a liquid, at -200℃.
SC2e drinking water
Desalination is where one produces pure water from sea water, which can be done so via simple distillation. The sea
water is heated so that water vapour leaves it, which is then cooled and condensed into water without the dissolved
salts. This requires a lot of energy, so is only used when energy is cheap/plentiful and sea water is abundant.
Chemical analysis involves chemical reactions or sensitive machines to identify and measure the substances in a
sample. The water used should not contain any dissolved salts, which may interfere, eg tap water could form
unexpected cloudy precipitates, leading to incorrect conclusions.
In the UK, raw material for producing drinking water comes from rivers,lakes or aquifers, which is usually stored in
reservoirs. These sources can contain objects like twigs and leaves, small insoluble particles such as grit and silt,
soluble substances like salts, pesticides and fertilisers, and bacteria/other potentially harmful microorganisms.
Different steps are needed: screening via a sieve, sedimentation where small particles are allowed to settle out,
filtration using beds of sand and gravel, then chlorination to kill microorganisms.
(SC3) SC3-Atomic Structure
(paper 1 and 2)
SC3
SC3a structure of an atom
In 1885 John Dalton published an atomic theory that said: all matter is made up of tiny particles called atoms, atoms
are tiny hard spheres that cannot be further broken down, atoms cannot be created nor destroyed, the atoms in an
element are all identical (but each has its own type of atom). Experiments towards the end of the nineteenth century
suggested they contained even smaller particles. JJ thomson found that cathode rays contained subatomic particles;
electrons. The atom contains a tiny but dense nucleus with protons and neutrons, surrounded by fast moving
electrons arranged in energy levels at differing distances from the nucleus. atoms have equivalent numbers of
protons and electrons; their charges cancel each other out leading to no charge. The diameter of an atom can be
100k times the diameter of its nucleus.
SC3b atomic number and mass number
In 1909 Ernest Rutherford and co were investigating the structure of an atom. Protons were fired at a one atom thick
layer of gold foil. Most particles passed through, a few being deflected and a very small number bounced back. With
this in mind, Rutherford suggested that atoms are mostly empty space, with a tiny and dense positive nucleus.
Elements in the periodic table were originally placed in order of mass, but due to very different properties, were
swapped around. Henry Moseley, in 1913, confirmed that this was correct, showing they were in order of the amount
of positive charge in the nucleus. in 1918 the proton was discovered.
The atomic number (Z) dictates how many protons are present in the element, all atoms of an element have the
same unique atomic number. The mass number(A) is the total amount of protons and neutrons, as the electron
number can be considered negligible.
, SC3c isotopes
In 1932 James Chadwick discovered the neutrons, which explained why atoms of the same element have different
masses (isotopes). The understanding of neutrons led to the discovery of nuclear energy. By firing neutrons at a
uranium isotope it was discovered that a nucleus can be split (nuclear fission), which produces new elements and
transfers large amounts of energy. Nuclear power stations use this energy to produce electricity.
The mass of an atom is incredibly small so we measure it relative to carbon-12. It is
used as a standard and is given a mass of exactly 12, of which all other atom masses
are compared to. All elements exist as a mixture of isotopes, the idea of which is used
to calculate the relative atomic mass of said element-Ar which is the mean mass of an
atom of an element compared with carbon-12. RAM is calculated using: total mass of
atoms/number of atoms.
(SC4) SC4-The Periodic Table
(paper 1 and 2)
SC4
SC4a elements and the periodic table
By 1869, 63 elements had been discovered. Mendeleev arranged them in order of ascending relative atomic masses,
though he did not always keep this order and left gaps. He often swapped positions if he thought that better suited
their chemical properties and those of their compounds. E.g. he swapped tellurium and iodine due to the physical
property even though their position was anomalous due to their relative atomic masses. He justified it by stating that
the relative atomic mass for tellurium was incorrect. Vertical columns contained elements with increasing relative
atomic masses, horizontal with similar chemical properties. by 1871 he had settled on a table in which elements with
similar properties were arranged into vertical columns. He used the gaps to make predictions about the properties of
undiscovered elements. One of which was eka-aluminium. Gallium, discovered shortly after in 1875, had properties
that closely fitted those predicted for eka-aluminium.
SC4b atomic number and the periodic table
At the end of the 19th century, a group of inert elements were discovered. These were easily fitted into group 0, but
did not explain iodine and tellurium. At first the atomic number simply dictated the atoms position in the table,
though Mosley showed instead it is a physical property. He fired high energy electrons at different elements, causing
them to give off X rays. For each step increase in atomic number, there was a step change in the energy of these rays.
He realised the atomic number was equal to the number of positive charges. The particle that carries it, the proton,
was discovered a few years later. Thus, the atomic number must be the number of protons in a nucleus.
Elements in the modern periodic table are arranged in ascending Z: elements in a row/period are in order of
increasing atomic number, elements with similar properties are in the same column, non-metals are on the right, the
iodine-tellurium pair reversal is explained. More X-ray analysis showed that only 7 elements between hydrogen and
uranium were left to be discovered, all between 1917-45. Neptunium the first element with an atomic number above
92 was discovered in 1940, these transuranium continue to be discovered and can all be placed in the periodic table.
SC4c electronic configurations and the periodic table
In atoms, electrons are found in shells around an atom. The way it is arranged is its electronic configuration. For the
first 20 elements, the shells can contain 2,8,8 electrons in each shell. These occupy the shells working from the
innermost outwards. The number of occupied shells is equal to the period number, the number of electrons in the
outer shell is equal to the group number except for group 0, which are full.
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