Chemistry Unit 3 - GCSE (entire syllabus)

Another one of my "home-made" revision packs! Just some notes of the entire syllabus! These are great to skim read before the exam as it has everything in quick easy bites (well as quick as can get) Good luck in your exams guys!!

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Chemistry
AQA ­ Unit 3
Brief History of the periodic table
Until recently there were two ways of categorising elements:
1) their physical and chemical properties
2) their relative atomic mass
In 1864, Newlands tried to arrange the elements in his law of octaves, but it was inconsistent and dismissed. Next,
Mendeleev placed them in order of atomic mass. Cleverly, he left gaps for unfound elements. Now-a-days Elements
in the same group have the same number of electrons in their outer shell. They also have similar properties
Group 1 ­ Alkali Metals
The alkali metals have 1 electron in their outer shell, and so need to lose one to have an outer shell of 8 electrons.
Boiling and melting points DECREASE going down the group. Reactivity increases going down the group. Their
hydroxides dissolve in water to give an alkaline solution. They all form IONIC compounds (do not share). Lastly, they
are all silvery solids
Group 7 ­ Halogens
All have 7 electrons in their outer-shell and only need one extra electron to get to their most stable place (a noble
gas), as every group wishes to do. Reactivity DECREASES going down the group, whilst the boiling and melting points
INCREASE going down the group. They all form molecules which are paired atoms. E.g. F2, Cl2. They are all non-metals
with coloured vapours, and react with metals to form salts. Lastly, they do both Ionic and Covalent bonding.
The Transition Elements
They are less reactive than group 1, as they have more electrons to lose, varying amount of electrons in their outer
shell, and they are very dense, strong and shiny. The compounds of a transition element are usually very colourful,
and they are good conductors of heat and electricity. They are used in many experiments as a catalyst. This means
that they speed up a reaction by making the reactants collide more often.
Acids and Alkalis
Acids all have a H+ ion in them, whereas alkalis all have an OH- ion. This makes them acids and alkalis. Firstly, in 1880,
Arrhenius first said that molecules ionised water, however, due to his inexperience many scientists ignored him. However,
Lowry and Bronsted made things a bit more general. The said that:
Acids release H+ ions ­ they are proton donors
Bases accept H+ ions ­ they are proton acceptors
A strong acid fully ionises in water, whereas a weak acid partially ionises in water
Titrations
These are used to find concentrations.
The point where the acid and base have completely reacted is known as the end point.

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Indicator used:
STRONG acid + weak alkali Methyl orange (think of oranges being acidic)
Weak acid + STRONG alkali Phenolphthalein
STRONG acid + STRONG alkali Universal indicator
A pipette is used to measure accurately a volume of this solution
A second chemical is placed in a burette. This other solution is of a chemical that will react with the synthesised chemical
sample in the conical flask.…read more

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Water
You must know the water cycle off by heart.
Here are the different processes you must know:
Precipitation ­ basically rain
Canopy interception - The precipitation that is intercepted by plant foliage Snowmelt
Runoff - The variety of ways by which water moves across the land.
Infiltration - The flow of water from the ground surface into the ground.
Subsurface Flow - The flow of water underground.
Evaporation - The transformation of water from liquid to gas.…read more

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Helps grow healthy bones and teeth
Disadvantages
Causes scum
Doesn't lather properly
Causes lime scale when boiled
Causes
Calcium sulphate/ chloride
Magnesium sulphate/chloride
From millions of years of running through rocks
Removal
Ion-exchange column (exchanges sodium and hydrogen for calcium and magnesium)
Washing soda
Energy
Exothermic reactions give OUT heat
Endothermic reactions take IN heat
Exothermic:
Burning
Neutralising acids and alkalis
Endothermic:
Electrolysis
Thermal decomposition of limestone in a blast furnace
Breaking bonds ABSORBS energy with a POSITIVE sign
FORMING bonds RELEASES energy with a…read more

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By adding Sodium hydroxide to some metals, we can attain what they are by recording the colour of the precipitate the form,
due to displacement. Here are the six you must know:
Calcium: white
Copper: blue
Iron (ll): sludgy green
Iron (lll): Reddish brown
Aluminium: white
Magnesium: white
However, if we add excess sodium hydroxide to aluminium, it dissolves
Testing for Anions
Heating strongly
To distinguish copper and zinc carbonate we can heat them up.…read more

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Organic ­ Yellow or blue flame
Testing for saturated bonds
Add bromine water
Unsaturated ­ water decolourises
Saturated: Colour will stay brown
Test for water
Anhydrous cobalt chloride paper
Turns blue to pink if water is present
Empirical Formula
These are used to find the equation of a compound. E.g. Find the empirical formula of methane if combustion produces 4.4g
of CO2 and 3.6g of H20.…read more

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