AQA GCSE CHEMISTRY UNIT 2 FOUNDATION

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Atomic Structure and Bonding (F)
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 be the same (e.g. O2) or different (e.g. H2O). The chemical formula shows the
number and type of atoms present. Nonmetal compounds are made of molecules:
Carbon dioxide contains CO2 molecules
Methane (natural gas) contains CH4 molecules
AN ION is an atom or group of atoms with an electrical charge (+ or ). Metal compounds such as
sodium chloride or copper sulphate contain ions.
Sodium chloride is made of Na+ and Cl ions
Magnesium Oxide is made of Mg2+ and O2 ions
Note that metals form positive ions while nonmetals form negative ions.
A solid is represented by (s). e.g. H2O(s) is ice.
A liquid is represented by (l) e.g. Fe(l) is molten iron.
A gas is represented by (g) e.g. H2O(g) is steam.
A solution in water is represented by (aq). Salt dissolved in water is NaCl(aq).
You should remember that the common gases are diatomic (have 2 atoms in each molecule). These
are Oxygen O2 Hydrogen H2 Nitrogen N2 and Chlorine Cl2.
Elementary Particles
Atoms are made up of smaller particles called protons, neutrons and electrons.
The protons and neutrons cluster together in a small nucleus at the centre of the atom while the
electrons orbit the nucleus.
The main properties of the particles are:
Particle Mass Charge
PROTON 1 +1
NEUTRON 1 0
ELECTRON Very Small 1
Every element has an atomic number, which is the number of protons in the nucleus.
Atoms are neutral, so that the number of electrons is the same as the number of protons.
The mass of an atom is almost entirely made up of protons and neutrons, which have the same mass
as each other (the mass of electrons can be ignored).
These relations can be summarised as:
ATOMIC NUMBER = NUMBER OF PROTONS
NUMBER OF PROTONS = NUMBER OF ELECTRONS
MASS OF ATOM = PROTONS + NEUTRONS
Examples:
Atomic Number Protons Electrons Neutrons Mass Number
Element
Na 11 11 11 12 23
C 6 6 6 6 12

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U 92 92 92 146 238
Electron Structure
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)
Fluorine has atomic number 9. Its electronic structure is 2.7
Sodium has atomic number 11. Its electronic structure is 2.8.1
Calcium has atomic number 20.…read more

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Giant Ionic Structures
Compounds of metals, such as sodium chloride (NaCl) or copper sulphate (CuSO4) are made
up of positive metal ions (e.g. Na+ ) and negative nonmetal ions (e.g. Cl).
The ions are arranged in a regular lattice so positive and negative ions are arranged
alternately in 3 dimensions.
1) They have high melting and boiling points.
2) They are hard but brittle (shatter easily)
3) They conduct electricity only when melted or dissolved in water.
4) Many ionic substances are soluble in water.…read more

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Enzymes are biological catalysts.
Other examples of catalysts are:
NAME PURPOSE
Aluminium Oxide Cracking of Oil
Iron Manufacture
of ammonia
Catalysts are very valuable in chemical industry, since they can be reused and they provide a much
cheaper way of speeding up a reaction than heating, so providing cheaper goods.
Temperature
Another way of controlling the rate of a reaction is by temperature. A rise of 10oC will roughly double
the rate of a reaction.…read more

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The rate of a reaction can be measured and followed on a graph, e.g.
Curve A represents a reaction between powdered zinc and sulphuric acid, while curve B represents a
reaction between lumps of zinc and the same amount of sulphuric acid. You should note:
a) That a steeper curve (A) represents a faster reaction.
b) That the curves start steeply, but then level off.…read more

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HYDRATED COPPER SULPHATE = ANHYDROUS COPPER SULPHATE + WATER
(Blue) (White)
If the hydrated copper sulphate is heated, it turns white as the water is given off. This requires energy
so the forward reaction is endothermic
When water is added to anhydrous copper sulphate, it turns blue and heat is given out so the reverse
reaction is exothermic. This reaction is sometimes used as a test for water.
In any industrial process it is necessary to minimise the amount of energy used.…read more

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Sodium Hydroxide: Making soap.
Electrolysis of Copper Sulphate Solution using Copper Electrodes
If copper sulphate (CuSO4) solution is electrolysed using copper electrodes instead of carbon
electrodes.
1. Copper dissolves away from the positive anode and
2. Copper is deposited at the negative cathode
3. The solution remains the same as it is losing copper ions at the cathode but gaining them at
the anode.
This is used industrially to purify copper.…read more

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Sulphuric acid H2SO4
Hydrochloric acid HCl
Nitric acid HNO3
Bases
1) Bases react with and neutralise acids.
2) Metal oxides and metal hydroxides are bases
3) ALKALIS are soluble bases
4) Alkalis produce OH ions in water.
Examples
1) These are soluble and are therefore alkalis as well as bases
Sodium hydroxide NaOH
Calcium hydroxide Ca(OH)2
Potassium hydroxide KOH
Ammonia NH3
2) These bases are insoluble
Magnesium oxide MgO
Copper oxide CuO
Salts
These are crystalline substances, generally compounds of metals.…read more

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H+ + OH = H2O
Making salts
Method 1. Used to make sodium, potassium & ammonium salts. An acid is to react with an alkali.
1) The alkali is measured out using a pipette, indicator is added, and enough acid is
added from a burette to just change the colour of the indicator.
2) The volumes of acid and alkali used are noted, and the experiment is repeated using
the same volumes, but no indicator.
3) The solution is evaporated to leave the salt.…read more

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