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Atoms, Molecules and Ions.
AN ATOM is the smallest particle of an element. They cannot be split into smaller particles in
chemical reactions. Iron is made of iron atoms (Fe). Sulphur is made of sulphur atoms (S)
A MOLECULE is a small group of atoms joined together.
The atoms may…

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The electrons orbit the nucleus in 'shells'. These can hold the following numbers of
electrons:

the innermost shell can contain up to 2 electrons
the next shell can contain up to 8 electrons
the next shell can contain up to 8 electrons (although this can be expanded up to 18)…

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carbon) are others are others. Because the bonds between all the atoms are very
strong:
1) They have very high melting points.
2) They are very hard (graphite is an exception)
3) They do not conduct electricity (graphite is an exception)
4) They are insoluble in all solvents.
The important…

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c) Mr of ammonium nitrate = 14 + 4 x 1+ 14 + 3 x 16 = 80
Percentage of nitrogen = 2x14x 100 = 35%
80
Empirical Formulae
This is the formula which shows the lowest whole number ratio of the atoms
e.g. Molecular formula = C2H4, Empirical Formula…

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e.g. the calculated mass of alcohol which could be obtained by fermenting some sugar is
4.6g of alcohol. The actual mass obtained in an experiment was 3.5g. Find the % yield.
Answer = 3.5 x 100 = 76.1%
4.6

The Mole
The mole is an important quantity used in all…

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Similarly, at the start of the reaction, concentrations of C & D will be low, but as the
reaction proceeds their concentrations will increase and so the reverse reaction becomes
faster.

Eventually, as the forward reaction gets slower and the reverse reaction gets faster, the
rates will eventually become equal.…

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4) Under these conditions, about 28% of the gases are converted to ammonia. This can be
separated from the unreacted nitrogen and hydrogen by cooling. Ammonia turns to a liquid
at -33C, while the other gases do not turn to liquids until much lower temperatures. The
unreacted gases can then…

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CONCENTRATION
The concentration of a solution is the amount of solute present in a solution. The
concentration is usually measured in moles per dm3 (1dm3 = 1 litre)
This means that equal volumes of solution of the same concentration contain equal number
of particles.
e.g. 25cm3 of a solution of…

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b) That the curves start steeply, but then level off. This is because the concentration of the
acid is high at the start of the reaction, but gets less as the acid is used up and eventually
stops.
c) That the amount of gas made by the end of the…

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Conductors
Metals and graphite are the only solids which conduct electricity, but no chemical change is
involved. Liquid (melted) metals also conduct, but again there is no chemical change.

Electrolytes
These are liquids which conduct electricity, and are decomposed by it. They are ionic
substances which are dissolved in water…

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