Summary Revision Notes: AQA GCSE Combined Science, Chemistry Paper One and Two
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Course
Science
Institution
GCSE
A detailed summary of all modules of the AQA course specification booklet for Chemistry (combined science, trilogy), with all the important information. These are the revision notes I used to achieve a 9-9 grade for my combined science GCSE.
Revision Notes
Atomic Structure and the Periodic Table
Atoms, Elements and Compounds
All substances are made up of atoms.
An atom is the smallest part of any element that can exist.
There are about 100 different elements.
Compounds are formed from the chemical reaction of elements, where the atoms of
each are in fixed proportions throughout the compound.
Chemical reactions always involve the formation of one or more new substance, and
often involve a detectable energy change.
Compounds can only be separated into elements by chemical reactions.
Mixtures
A mixture consists of two or more elements or compounds not chemical combined.
The chemical properties of each substance in the mixture have not been changed.
Mixtures can be easily separated by physical techniques such as filtration,
crystallisation, simple/fractional distillation, and chromatography.
Chromatography
This technique is used to separate compounds out of a mixture.
Draw a line in pencil near the bottom of a sheet of filter paper.
Add a spot of ink to the line and place the sheet in a beaker of solvent e.g., water.
The solvent used depends on what is being tested. Some compounds dissolve well in
water, but sometimes other solvents, like ethanol, are needed.
Make sure the ink is not touching the solvent.
The solvent seeps up the paper, carrying the ink with it.
Each different dye in the ink will move up the paper at a different rate so the dyes
will separate out.
If any of the dyes in the ink are insoluble with the dyes you have used, they will stay
on the base line.
Take the filter paper out and leave it to dry. The result is a pattern of spots, called a
chromatogram.
Simple Distillation
This is used to separate out a liquid from a solution.
The solution is heated, and the part of the solution
that has the lowest boiling point will evaporate
first.
The vapour is the cooled, condensed and is then
collected.
, The rest of the solution is left behind in the flask.
The problem with simple distillation is that you can only use it to separate things
with very different boiling points.
Filtration
This is used to separate an insoluble solid from a liquid.
Set up a beaker and put a funnel over it, with a piece of filter paper in it.
Pour the solution into the funnel and let it filter through, leaving behind the solid.
Crystallisation
This is used to separate a soluble salt from a solution.
Pour the solution into an evaporating dish and gently heat the solution. Some of the
solvent will evaporate and the solution will get more concentrated.
Once some of the solvent has evaporated, or when crystals start to form, remove the
dish from the heat and leave it to cool.
The salt should start to form crystals as it becomes insoluble in the cold, highly
concentrated solution.
Filter the crystals out of the solution and leave them in a warm place to dry.
The Development of the Model of the Atom
John Dalton believed that atoms are solid spheres, and that there are different types
of atoms. He tried to produce a list of the atoms in weight order.
J.J Thompson discovered electrons and came up with the plum pudding model of the
atom.
Rutherford, 1911, did the alpha particle scattering experiment that led him to the
conclusion that atoms are mostly empty space, and that they had a positively
charged nucleus. He came up with the nuclear model.
Niels Bohr suggested that electrons orbit the nucleus at specific distances.
James Chadwick provided evidence to show the existence of neutrons within the
nucleus, in 1932.
Relative Charges of Subatomic Particles
Protons have a charge of +1.
Electrons have a charge of -1.
Neutrons have a charge of 0.
Atoms have no overall electrical charge.
In an atom, the number of protons is equal to the number of electrons.
The number of protons is the atomic number.
The number of protons and neutrons is the mass number.
Size and Mass of Atoms
Atoms are very small and have a radius of about 0.1nm (1x10^-10m).
The radius of a nucleus is less than 1/10,000 of that of an atom (about 1x10^-14m).
, The relative mass of a proton/neutron is 1.
The relative mass of an electron is very small.
An atom of the same element, but has a different number of neutrons, is called an
isotope.
Relative Atomic Mass
The relative atomic mass of an element is a value that considers the abundance of
the isotopes of the element.
Electronic Structure
The electrons in an atom occupy the lowest available energy shells (the inner shells).
The Periodic Table
The elements in the periodic table are arranged in order of atomic number so that
elements with similar properties are in columns, known as groups.
Elements in the same group in the periodic table have the same number of outer
shell electrons, giving them similar chemical properties.
Developing the Periodic Table
Before the discovery of protons, neutrons and electrons, scientists attempted to
classify the elements in order of their atomic weight.
The early periodic tables were incomplete, and some elements were placed in
inappropriate groups if the strict order of the atomic weights was followed, as this
did not consider their properties.
Mendeleev overcame some of these problems by leaving gaps for undiscovered
elements. To order them, he mainly followed atomic weights, but changed them
around if the elements properties required him to.
Elements with properties predicted by Mendeleev were discovered and filled the
gaps.
Metals and Non-Metals
Metals react to form positive ions.
Non-metals do not form positive ions.
Group 0
These are called the noble gases.
They are unreactive and do not easily form molecules because their atoms have
stable arrangements of electrons.
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