AQA Chemistry Unit 3 Key Points Summary

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History Periodic Table
In early 1800s didn't know of protons or electron ­ no atomic numbers
Newlands ­ every 8th element had similar properties
Newlands Octaves
Organised by increasing atomic mass
Work was criticised as:
Groups had elements without similar properties (carbon and titanium)
Mixed up metals and non metals (iron and oxygen)
Didn't leave gaps for undiscovered elements
Mendeleev put element in increasing atomic mass
Left gaps in groups for elements with similar properties but not discovered yet
The gaps predicted the properties of undiscovered elements
Periodic Table
In late 19th century we discovered protons, neutrons and electrons
Periodic table matched up to what we had discovered about the structure of the atom
Elements in the same group have the same number of electrons in their highest energy
Positive charge of nucleus attracts electrons and holds them in place
The further the electron is from the nucleus the less the attraction
Attraction is less when lots of inner electrons get in the way of the nucleus charge,
reducing the attraction ­ SHIELDING
Combination of increased distance and shielding means an electron in a higher energy
level is more easily lost as weaker attraction.
That's why group 1 metals get more reactive
BUT shielding and distance means it is harder to gain an electron, less attraction from
the nucleus pulling electrons in
Why group 7 elements get less reactive
Group 1 Alkali Metals
Must be stored in oil and handled with forceps
~More reactive
~Lower melt and boil point
~Low density
Lithium, Sodium and potassium
Form ionic compounds with non metals as keen to lose their one outer electron to form
a 1+ ion
They produce white compounds that dissolve in water to form a colourless solution
They react vigorously with water
Float and move on the surface fizzing
Produce hydrogen
Potassium gets hot enough to ignite it
Lighted splint will indicate hydrogen as there will be a squeaky pop
Form hydroxides that dissolve in water to give alkaline solutions
Group 7 Halogens
~Less reactive
~Higher melt and boil point
All halogens are non metals with coloured vapours
Fluorine is very reactive ­ poisonous yellow gas

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Chlorine is fairly reactive ­ poisonous dense green gas
Bromine ­ dense poisonous red/brown volatile liquid
Iodine ­ dark grey crystalline solid or purple vapour
All molecules are pairs of atoms
Form 1 ions called halides
More reactive halogens can displace a less reactive halogen from an aqueous solution
of its salt
Cl2 + 2KBr > Br2 + 2KCl
Transition Elements
Good conductors of heat and electricity
Dense, strong and shiny
Less reactive than group 1 metals
Often have more than one ion
Fe2+& Fe3+,…read more

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Imported water contains more hardness than local water
Local water is only temp hardness as all hardness is removed by boiling
Imported contains both temp and perm hardness as still some hardness after boiling
Local and imported water contained the same amount of temp harness.…read more

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Ammonia breaks down into nitrogen and hydrogen until reaches equilibrium
TEMP: 450oC
Pressure is set as high as possible to give best % yield
Forward reaction is exothermic, so the yield of ammonia would be greater at a lower
BUT lower temp = lower rate of reaction
So they increase the temp anyway to get a faster rate.…read more

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Don't ionise completely so just a weak acidic solution
(Concentration is how watered down your acid is
Strength is how well it has ionised)
Ethanoic acid can be made by oxidising ethanol
Ethanol + oxygen Ethanoic acid + water
Ethanoic acid can be dissolved in water to make vinegar ­ flavourings and preserve
Citric acid used to make fizzy drinks and to get rid of scale
Carboxylic acids with longer chains of carbon atoms ­ soaps and detergents
Carboxylic acids used in the preparation…read more

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Mol/dm3 = mol / dm3)
~~Number of moles = mass (g) / RFM
~EXAMPLE 1 ­ if they ask fOR concentration in MOLES per dm3
25cm3 of sodium hydroxide in a flask and the concentration is 0.1mol/dm3
Find from titration that it takes 30cm3 of sulfuric acid to neutralise
1000cm3 = 1dm3
STEP 1 work out how many moles of the "known" substance you have
Number of moles = concentration x volume
= 0.1mol/dm3 x (25/1000) dm3 = 0.…read more

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In an exothermic reaction, the energy released in bond formation is greater than
energy used in breaking old bonds
Energy and Fuels
Measure amount of energy released when fuel is burnt by burning the fuel to heat up
Uses a glass or metal container ­ good conductors of heat
1. Mass of spirit burner + lid before heating = 68.75g
2. Mass of spirit burner + lid after heating = 67.…read more

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Bond energies you need are
HH: +436kJ/mol ClCl: +242kJ/mol HCl: +431kJ/mol
1. Breaking 1 mole of HH and 1 mole of ClCl bonds requires 436+242=678kJ
2. Forming 2 moles of HCl bonds releases 2x431=862kJ
3. Overall more energy is released than is used to form the products: 862678=
184kJ/mol released
4.…read more

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Key for Ionic Reaction column
Red means solid. Black means aqueous
Metal Colour of precipitate Ionic reaction
Calcium, Ca2+ White Ca2+ + 2OH Ca(OH)2
Copper(II), Cu2+ Blue Cu2+ + 2OH Cu(OH)2
Iron(II), Fe2+ Green Fe2+ + 2OH Fe(OH)2
Iron(III), Fe3+ Brown Ca3+ + 3OH Ca(OH)3
Aluminium, Al White at first.…read more


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