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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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Atomic Number Protons Electrons Neutrons Mass Number

Na 11 11 11 12 23

C 6 6 6 6 12

U 92 92 92 146 238
Electronic Structure
The electrons orbit the nucleus in 'shells'. These can hold the following numbers of

the innermost shell can contain up to…

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3) They do not conduct electricity
Simple molecular substances are nearly always non-metallic elements or their compounds.
e.g. Water (H2O), Iodine (I2), Carbon dioxide (CO2), Sugar (C12H22O11).

Giant Covalent Substances
In these substances, strong covalent bonds join atoms together in large numbers to make
giant structures. Sand (silicon dioxide) is…

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Mg(NO3)2 = 24 + (14 + 3x16)x2 = 148

Percentage Calculations
If you need to find the percentage of an element E in a compound, you use tormula

Percentage = Ar of E x No of atoms of A x 100
Mr of compound

e.g. Find the percentage of nitrogen…

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What mass of carbon dioxide is obtained by burning 3g of C2H6?
2C2H6 + 7O2 = 4CO2 + 6H2O
Mr: C2H6 = 30, CO2 = 44
Answer = 3 x (4x44) = 0.05 x 176 = 8.8g
Atom Economy
This is given as Formula Mass of all molecules of…

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If a reaction is exothermic in one direction, it will be endothermic in the other direction and
the amount of heat given out by the exothermic reaction will be equal to the amount of
heat taken in by the endothermic reaction.

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Manufacture of Ammonia
1) Ammonia is made from nitrogen and hydrogen. Nitrogen is separated from air, while
hydrogen is obtained by the cracking of oil.
2) The equation for the reaction is:
Nitrogen + Hydrogen Ammonia (exothermic)
N2 + 3H2 2NH3
3) The conditions needed for the reaction are…

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Aluminium Oxide Cracking of Oil

Iron Manufacture of

Vanadium Pentoxide Manufacture of sulphuric acid.

Most of these catalysts are solid substances, used to catalyse reactions between gases.
They do this by
allowing the gas molecules to collect on their surface where they are close enough to react


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The rate of this reaction can be measured by seeing how much hydrogen gas is given off in
one minute. This rate can be increased by:
1) Raising the temperature of the reaction.
2) Using more concentrated sulphuric acid.
3) Using powdered zinc rather than lumps.
4) Adding some copper,…

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Energy changes in reactions
Reactions which give out energy are called Exothermic. They cause the temperature to rise.
Many reactions are exothermic, including all burning (combustion) reactions
e.g. 2Mg + O2 = 2MgO
Reactions which take in energy are called Endothermic. They may cause the temperature to
fall. Thermal decompositions…


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