GCSE AQA Chemistry Unit 3

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ELEMENTS, ACIDS AND WATER
The Periodic Table:
Early 1800's: only went on atomic mass.
Newlands Law of Octaves (1864) ­ every 8th element with similar properties. Pattern failed in 3rd row
due to transition metals. Criticised as - He left no gaps. ­groups contained some not similar ­ Mixed
metals and non metals
Mendeleev (1869)- left gaps to keep similar properties in same vertical groups. and put elements in
order of atomic mass.
Late 19th century, protons, neutrons and electrons discovered, summary of atomic structure.
Modern table: electrons are set out in shells which correspond to n energy level, the maximum
electrons that can occupy each level has the formula 2x n^2, e.g energy level 1 has 2 electrons.
Other than transition, all elements in same group have same number of electrons in outer, whereas
what period it is in is determined by the number of shells.
Further from nucleus, less attraction. SHEILDING! Group one metals are more reactive as you go
down the group for this reason. Group 7 less reactive as you go down as it means it is less likely to
gain electron.
Group 2 = alkaline earth metals, Middle = transition metals, 0=noble gases
Transition metals are less reactive as you go to the right, they are catalysts.
The Alkali Metals (group 1):
AS YOU GO DOWN : Larger atoms ­ extra full shell, more reactive ­ less attraction to nucleus, higher
density ­ more mass, lower melting and boiling points.
They form +1 ions as when they react, they lose an electron.
They never bond covalently, only forming ionic compounds
When they react with water, they form a hydrogen gas. They fizz vigorously and produce hydrogen
(squeaky pop). Hydroxide solution.
The Halogens (group 7):
AS YOU GO DOWN: less reactive ­harder to attract an electron, higher melting and boiling points.
Vapour colours- Fluorine makes a yellow gas that's poisonous, chlorine makes a green gas that's
poisonous, bromine makes a poisonous red-brown liquid and iodine is a dark grey solid or purple
vapour.
They form molecules (pairs) and bond both ionically (-1 atoms) and covalently.
React with metals to form salts, and more reactive ones will displace less reactive ones.
Transition Elements:
Good conductors, dense, strong, less reactive than group 1, higher melting point.
They will have more than one ion, and the different ions form different colour compounds.
Good catalysts! Such as iron used in Haber process and nickel for turning oil into fats.
Overlapping 3rd and 4th shells cause there to be different properties.
Acids and Alkalis:
Arrhenius said acids release hydrogen ions in water and that alkalis form hydroxide ions.
People disagreed due to ammonia gas reacting as a base not in water and many didn't agree that
these formations were possible as subatomic particles has no yet been discovered.
Lawry said, with both soluble and insoluble bases, acids are proton donors and bases are proton
acceptors.

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These were accepted as it explained acid behaviour. Also it was adaption of already working idea.
IN ACIDIC SOLUTIONS: acid molecules dissociate to release H+ ions, which then become hydrated.
IN BASIC SOLUTIONS: water molecules dissociate into H+ and OH-, but some take hydrogen ions,
leaving excess OH-. Other beses release OH- into solution.
Titration:
Strong acids (pH 1 or 2) ionise completely in water (every hydrogen atom released and becomes a
hydrated proton) but weak acids ionise slightly.…read more

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ENERGY AND CHEMICAL TESTS
Energy:
Exothermic ­ gives out energy to surroundings, normally in heat form and rise in temp.
Endothermic ­ the opposite!
Measure energy produced by temp before and after. Large amount of energy lost to surround :/
reduce by putting cup in cotton wool as insulation.
Energy must be supplied to break bonds (endothermic) ­ the energy required to break old bonds is
greater than energy released. and energy is released when bonds form (exothermic.…read more

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Experimental mass
Divide that mass by the relative atomic mass.
Ratio.
Instrumental methods:
faster, accurate, technicians, not chemists. expensive.
Atomic Absorption Spectroscopy ­ metals. Recognises pattern.
IR Spectrometry ­ pattern of absorbance is unique.
UV spectrometry.
NMR spectroscopy ­ ORGANIC COMPOUNDS, what atoms hydrogen connects to.
Gas-liquid chromatography.
Mass Spectrometry.…read more

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