AQA Chemistry Unit 3

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Chemistry 3 Revision
Periodic Table
John Dalton ­ 1808
o Arranged periodic elements in order of mass
o Measured in chemical reactions
o Published in his book ­ A New System of Chemical Philosophy
AlexandreEmile Beguyer de Chancourtois ­ 1862
o Noticed every 8th element was the same
o Showed similarities between each 8th element
o Produced clear diagram
o When published diagram was missed out
John Newlands ­ 1863
o Law of octaves
o Noticed that every 8th element was similar
o Didn't leave room for new elements ­ new elements were being found regularly
o Some elements that were grouped in the same octave weren't similar at all
o Different elements were put in the same place
o Work ridiculed
Dmitri Mendeleev ­ 1869
o Placed in order of atomic mass
o Arranged so that both physical and chemical properties could be seen
o Left gaps for undiscovered elements
o Predicted what the properties of the undiscovered elements would be ­ new elements almost
exactly matched Mendeleev's predictions
Elements arranged by proton number
Elements in the same group have similar properties ­ same number of electrons in the outer shell
Larger atoms lose electrons more easily
Smaller atoms gain electrons less easily
o Happens because the outer shells are further away from the nucleus and the inner shells `shield'
the outer shells from the positive charge.
o Group 1 loses electrons to form chemical bonds
o Group 7 gains electrons to form chemical bonds
o Group 1 ­ Alkali Metals
Reactivity increases going down the group
The outer electron is easier to lose ­ becomes more reactive lower down the group
o Group 2 ­ Halogens
Reactivity decreases going down the group
Less positive charge reaches the outer shells so it is harder to gain an electron
Reactive metals (Group 1 and 2)
o React viciously with other elements and water
o Easy to cut
Transition metals
o Contains unreactive metals
o Also known as `noble metals'
Nonmetals

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Low melting and boiling points
o Many are liquids or gases at room temperature
Noble Gases
o Very unreactive elements
o Very difficult to make them react with other elements
Group 1 ­ Alkali Metals
o Very reactive ­ stored in oil to stop them from reacting with oxygen in the air
o Low density ­ lithium, sodium and potassium float on water
o Oxidise quickly
o Soft ­ can cut with a knife
o Only need to lose 1 electron to become stable
o…read more

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Covalent bonds
Both have electrons to make stable
Hydrogen Chloride (HCl)
o More reactive halogen can displace less reactive halogen
Transition elements
o Giant structure held together by metallic bonds
o Outer electrons of each atom can move freely within the metal delocalised
o Good conductors ­ delocalised electrons can carry the current/heat through the metal
o Hard, tough, strong
o Have high melting/boiling points ­ except mercury
o Partly filled inner shells form brightly coloured compounds ­ can be used as catalysts
o Properties…read more

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Strong acid + strong alkali ­ only neutralise if there were the right quantities in the first place
o More acid than alkali ­ all the alkali will be neutralised but the solution will be acidic
o More alkali than acid ­ acid will be neutralised and solution will be alkaline
o End Point = when all the acid and the alkali have reacted completely
o When strong acid and weak alkali react together ­ end point solution is acidic
o Indicators
Strong acid +…read more

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Solubility
o Many gases are soluble in water
o Many ionic compounds are also soluble in water
o Impossible to dissolve covalent substances in water ­ little attraction between the molecules in the
substance and the molecules in the water
o Solute ­ Solvent ­ Solubility
o Solubility measured in grams of solute per 100g of solvent at a specific temperature
o Solubility increases as the temperature increases
o Saturated solution ­ as much solute as possible has been dissolved into the solvent
As a…read more

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Contains calcium and magnesium compounds ­ dissolve when streams and rivers run over rocks
containing these compounds
o Sodium stearate (soap) + Ca2+ and Mg2+ ions calcium/magnesium stearate (scum) + Na+ ions (soluble
in water)
o Hard water also leads to scale
Scale is a poor conductor of heat
Is created near or around hot water pipes
Ca2+ (aq)(hardness) + 2HCO3(aq) heat CaCo3 (s) (lime scale) + H2O (l) + CO2 (g)
o Some compounds in hard water are good for the health
Removing hardness…read more

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Energy Calculations
Not all fuels produce the same amount of energy when they burn
Some reactions are more exothermic than others
Bomb Calorimeter ­ instrument used to measure how much energy a fuel produces when it burns
o The fuel is burnt under a beaker of water
o Temperature change is then measured after the food is burnt
The amount of energy in food is measured in the same way
Energy has to be supplied to break bonds ­ endothermic reaction
Energy is released when…read more

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Flame
Tests
Element Flame colour
Lithium Bright red
Sodium Golden yellow
Potassium Lilac
Calcium Brick red
Barium Green
Analysis
Tests for positive ions
o Sodium hydroxide solution
White precipitates
Aluminium ­ dissolves when more solution is added
Calcium
Magnesium
Coloured precipitates
Copper (II) ­ Light blue
Iron (II) ­ Dirty green
Iron (III) ­ reddish brown
Ammonium ions
Reacts with solution to form ammonia and water
When the solution is warmed, ammonia gas is given off
Detected using red litmus paper ­ turns blue because…read more

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Produce white precipitate when hydrochloric acid is added followed by barium chloride
solution
White precipitate is barium chloride
Ba2+ (aq) + SO42 (aq) BaSO4 (s)
o Nitrates
Add sodium hydroxide and warm it
If no ammonia is detected ­ aluminium powder is added
Aluminium powder reduces the nitrate ions to ammonia ions
Red litmus paper test
Test for organic substances
o Inorganic substances ­ when substances return to their original state cooled
o Organic substances ­ substances which are based on carbon
o Unsaturated hydrocarbons…read more

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Used to measure the concentration of a metal in a liquid sample
o Mass Spectrometer
Used to compare the mass of the different atoms
Also identifies different elements
o Chromatography
Used to separate different compounds in a mixture
Technique is based on how well they dissolve in a solvent
Gasliquid chromatography
Used to separate compounds that vaporise easily
Gel Permeation chromatography
Separates compounds according to the size of their molecules
Ionexchange chromatography
Separates compounds with differently charged particles
Highperformance liquid chromatography
Separates compounds in solution…read more

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