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EL Revision Notes
(a) atomic number, mass number, isotope, Avogadro constant (N​A​), relative isotopic mass, 
relative atomic mass (A​r​ ), relative formula mass and relative molecular mass (M​r​) 
●
●
●

●

Atomic number - the number of​ protons in the nucleus​ of an atom
...
 
Mass number - the ​combined relative masses​ of p
​ rotons​ and ​neutrons​ (​nucleons​) in 
the nucleus of an atom
...
Isotopes have the​ same chemical properties​, 
but will have​ slightly different physical properties​ (such as d
​ ensity ​and r​ ate of 
diffusion​)
...
022x10​23​ mol​-1​
...
 

 
●
●
●
●

Relative isotopic mass - The mass of an atom of an isotope compared to 1/12 of the 
mass of a carbon-12 atom
...
 
Relative formula mass - The sum of relative atomic masses of all atoms in a compound
...
 
Relative molecular mass - The average mass of one molecule of an element compared to 
1/12 of an atom of carbon-12
...
 

●

Mass spectrometry​ can be used to determine r​ elative atomic mass​, r​ elative molecular 
mass​,​ relative isotopic abundance​ and m
​ olecular structure (PL topic)​
...
 
The gaseous particles are i​ onised​ by​ bombardment of high energy electrons​
...
 
The ions are ​accelerated​ to the s​ ame kinetic energy​ by an​ electric field​
...
This is 
dependent on the ion’s​ mass​ and c​ harge​
...
 

●
 
 
 
 
 
 
 
 
 
 
(b) (i) the concept of amount of substance (moles) and its use to perform calculations 
involving: masses of substances, empirical and molecular formulae, percentage composition, 
percentage yields, water of crystallisation
...
 
Balanced equations tell you​ reaction stoichiometry​ - x moles of one reactant react with 
y moles of another
...
 
Molecular formula - the a
​ ctual number of atoms​ in the compound
...
g
...
 
Actual yield is​ never 100% ​of the theoretical yield: 
○ Not all reactants fully react​
...
 
○ Two or more​ reactions may occur ​simultaneously​, producing unwanted 
by-products​
...
 

●

% yield ​= (​ actual yield/theoretical yield) x 100% 

●
●

Some molecules contain incorporated water molecules - water of crystallisation
...
 

●

Hydrated compounds lose their water when heated, so if the mass of hydrated and 
anhydrous salt is known, the formula of hydrated salt can be determined
...
 

 

1
...

3
...

5
...
 
Place a weighing bottle or boat onto the balance and add the required amount of solid
...
 
Empty the solid into glassware where it will be needed
...
 
 
N
...
​ Some solids (such as NaOH, CaCl​2​) readily absorb water from the atmosphere, so accurate 
weighing is not possible
...
 

 

●
●

n ​=​ cv 
To convert between ​moldm​-3​ and g
​ dm​-3​: 
 
 
 
 

●

The concentration of a solution depends on: 
○ The mass of solute  
○ The final volume of solution 

●

A s​ tandard solution​ is a solution of a​ known concentration​
...
 
 

 
 
 
 
 
 
 

 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

(ii) the techniques and procedures used in experiments to measure volumes of solutions; the 
techniques and procedures used in experiments to prepare a standard solution from a solid 
or more concentrated solution and in acid–base titrations  

 

Measuring volumes of solutions: 
● Measuring cylinders and beakers may be used to measure out a r​ ough​ volume of liquid
...
 
● Pipettes: 
○ Ensure pipette is clean by​ rinsing with distilled water followed by ​some of the 
solution t​ o be pipetted
...
 
○ Allow the liquid to run off into glassware​ until it stops​
...
  
○ Do not force the last few drops from the pipette​ as the apparatus is c​ alibrated 
to deliver t​ he required volume without adding the last drops
...
 
○ Ensuring the tap is closed, pour in the solution to be measured using a​ funnel​ so 
that the m
​ eniscus is above the 0 line​
...
 
Ensure the​ jet is full ​of the solution and there are ​no air bubbles ​present
...
Record the​ initial burette reading to the nearest 0
...
 
○ Run the required volume of solution from the burette into a suitable transfer 
vessel
...
Accurately weigh the solid using a weighing 
bottle and balance to 2d
...
 
● Pour 100cm​3​ of deionised water into a 250cm​3 ​beaker, transferring all of the measured 
solute into it
...
 
● Stir the mixture to completely dissolve the solute
...
Wash the beaker and stirring rod 
with deionised water, transferring the washings to the volumetric flask
...
Swirl at fixed intervals to ensure the solution is thoroughly mixed
...
 

●

Insert a stopper and invert the flask a few times to ensure thorough mixing
...
 
● Use a pipette filler to rinse a clean 25cm​3​ pipette with the stock solution
...
 
● Add deionised water to make up the rest of the volume (same procedure as making a 
standard solution from a solid)
...
Run off a 
little acid into a waste beaker to fill the jet and set the meniscus on a graduation line
...
05cm​3​
...
  
● Add two or three drops of suitable indicator (phenolphthalein or methyl orange) to the 
conical flask and swirl to mix
...
 
● Run the acid into the conical flask until the first signs of a permanent colour change 
appear (when the end point is reached)
...
Record the final burette reading and subtract 
from the initial to give the titre
...
 
● Repeat step 3 and 4
...
 
● Repeat the accurate titrations until you have 3 concordant titres (within 0
...
 

 
 
 

 
Common indicators used for acid-base titrations: 
● Indicators that change colour abruptly over a small pH range are needed to find the 
exact moment that the end point has been reached: 
○ Phenolphthalein - changes from colourless to pink when adding alkali to acid 
○ Methyl orange - changes from red to yellow when adding alkali to acid  
● Indicators such as universal indicator are too gradual to accurately determine end point
...
 
 
(d) balanced full and ionic chemical equations, including state symbols 
 
 
 
 
 
 
 
 
 

 

 
(e) conventions for representing the distribution of electrons in atomic orbitals; the shapes 
of s- and p-orbitals
...
Each shell is given a 
principal quantum number​
...
 
Shells contain different types of s​ ub-shell​
...
 

 
Subshell 

Number of orbitals 

Maximum electrons 

s 

1 

2 

p 

3 

6 

d 

5 

10 

f 

7 

14 

Shell 

Sub-shell 

Total number of electrons 

1 

1s 

2 

2 

2s 2p 

8 

3 

3s 3p 3d 

18 

4 

4s 4p 4d 4f 

32 

 
 

 
●
●
●

Orbitals are a bit of space that an electron moves in
...
 
Electrons pair up in orbitals and must spin in opposite directions - called ​spin-pairing​
...
 

 
 
 
 
 
●
●
 
 

P orbitals are d
​ umbbell shaped​
...
 
Electrons can be represented by arrows in boxes
...
 

 
 
(f) the electronic configuration, using sub-shells and atomic orbitals, of:  
 
(i) atoms from hydrogen to krypton  
Mg: 1s​2​2s​2​2p​6​3s​2​ or [Ne]3s​2 
Kr: 1s​2​2s​2​2p​6​3s​2​3p​6​3d​10​4s​2​4p​6​ or [Ar]3d​10​4s​2​4p​6 
 

Cr: ​[Ar]3d​5​4s​1 
Cu: [Ar]3d​10​4s​1 
 

Chromium and copper are exceptions
...
This is thought to be because this configuration is more 
electrically stable​
...
 

 
 
(g) how knowledge of the structure of the atom developed in terms of a succession of 
gradually more sophisticated models; interpretation of these and other examples of such 
developing models  
Dalton’s atom 
● Ancient greeks believed matter consisted of​ indivisible particles​
...
 
● John​ Dalton ​described atoms as​ solid spheres​ where d
​ ifferent spheres make up 
different elements 
 
Plum pudding model 
● JJ Thomson did a series of experiments to conclude atoms​ were not solid and 
indivisible​
...
 
● The ‘​plum pudding​’ model was created - a​ positively charged sphere ​with n
​ egatively 
charged electrons​ embedded within it
...
   
● Alpha particles​ were fired at a t​ hin sheet of gold​
...
 
● This suggests a t​ iny positive​ (due to ​deflection​)​ nucleus​ at the centre where most of 
the​ mass is concentrated​
...
 
 
● Henry​ Moseley d
​ iscovered that the​ positive charge of the nucleus increased in units of 
one​ from ​one element to the next​
...
 
 
● James ​Chadwick​ discovered the existence of the ​neutron​, a nucleon with​ mass but no 
charge​
...
 
 
Bohr model 
● A c​ loud of electrons is not possible​, as it would ​spiral down​ into the nucleus and 
collapse
...
 
● Each shell has a ​fixed energy level​
...
 
● Because the energy levels are fixed in position and have the same energy, the 
frequency of radiation emitted/absorbed will be constant​
...
 
 
Quantum model 
● The Bohr model is not perfect, but it is still in use due to its​ simplicity and ability to 
explain experimental observations​
...
You can never know where an 
electron is or the direction it is travelling in at any moment, but you can say how likely it 
will be that an electron is in a particular place at any point in time
...
 
 

 
 
 

(h) fusion reactions: lighter nuclei join to give heavier nuclei (under conditions of high 
temperature and pressure); this is how certain elements are formed 
 
● Nuclear fusion - When​ two small nuclei combine​ under ​high temperature​ and​ pressure 
to make ​one larger nucleus​
...
 
● Heavy elements (​ greater than Iron) can only be formed inside stars under huge 
temperatures and pressure
...
  
 
 
 
(i) chemical bonding in terms of electrostatic forces; simple electron ‘dot-and-cross’ 
diagrams to describe the electron arrangements in ions and covalent and dative covalent 
bonds 
● Ions form when electrons are​ transferred​ from one atom to another
...
  

 
 
 
 
 
 
 
 

●

 
 
 
 

 
 
 
 
 
 

In covalent bonding, two atoms share electrons so they both receive full outer shells
...
There is also a repulsion between the two nuclei, so a balance between the 
forces is necessary to hold the bond together
...
  

Exceptions 
● Sometimes, compounds may form without a full number of electrons in their outer shell: 
○ Boron trifluoride (BF​3​) only has​ 6 e
​ lectrons in its outer shell
...
 
 
 
 
 
 
(j) the bonding in giant lattice (metallic, ionic, covalent network) and simple molecular 
structure types; the typical physical properties (melting point, solubility in water, electrical 
conductivity) characteristic of these structure types 

 

 
Ionic lattice 
● Regular structure of ions form a crystalline structure
...
 
● Structure determines physical properties: 
○ Conduct electricity when molten or aqueous, 
not when solid
...
 
○ High melting point
...
Lots of energy is required to 
overcome these forces
...
 
Simple molecular 
● Simple molecules (such as O​2​, N​2​, CH​4​) consist of at least two atoms bonded together 
by covalent bonds
...
 
■ No giant structure needs to be broken down
...
 
○ Do not conduct electricity
...
 
○ Are insoluble or partially soluble in water
...
 
 
 
Giant covalent network 
● Some compounds form giant covalent lattices such as SiO​2​ and diamond (an allotrope of 
carbon)
...
  
● Physical properties: 
○ Very high melting point
...
 
○ Extremely hard
...
 
○ Good thermal conductors
...
 
○ Insoluble in polar solvents
...
 
○ Do not conduct electricity
...
  
■ Graphite is an exception
...
These act as charge carriers
...
 
● The positive ions are closely attracted to the ‘sea’ of delocalised electrons, forming a 
metallic lattice
...
 
■ Strong metallic bonding
...
Na​+​ only gives one 
delocalised electron while Mg​2+ 
gives two, so metallic bonding in 
Mg metal is stronger
...
 
■ No bonds holding the ions together, so they can slide over each other 
when pulled, so can be bent and stretched into a wire
...
 
■ Delocalised electrons can transfer kinetic energy
...
 
■ Delocalised electrons act as charge carriers
...
 
■ Metallic bonds are too strong for solvents to overcome
...
 
● Lone pairs of electrons repel more than bonding pairs, reducing the bond angle by 
lone-pair repulsion
...
 
● Lone pairs roughly reduce bond angles by 2
...
 
 
 
 
 
 
 
 
 

Molecule/Ion 

Bonding pairs 

Lone pairs 

Bond angle (​o​) 

Shape 

BeCl​2 

2 

0 

180 

Linear 

BF​3 

3 

0 

120 

Trigonal planar 

CH​4 

4 

0 

109
...
5 

Bent  

SF​6 

6 

0 

90 

Octahedral 

NH​4​+ 

4 

0 

109
...
 

 

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Arranged into periods (rows) and groups (columns) with elements ordered by atomic 
number (number of protons)
...
 
All elements within one group have the same number of outer shell electrons
...
 
s-block, p-block and d-blocks give information about the electron configuration of an 
atom of an element
...
The ionic radius is smaller in period 2 and the ions gain more delocalised 
electrons (as number of outer shell electrons increase) further along the period, 
increasing charge density
...
 

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●

●

Elements with giant covalent lattices (C and Si) have the largest melting points in their 
periods
...
 
Simple molecular molecules’ melting points depend on the strength of intermolecular 
forces (id-id forces) which are generally weak, hence the low melting points
...
 
The noble gases are monatomic, so have the weakest id-id forces of attraction, hence 
the lowest melting point in the periods
...
 
Reactivity increases down the group as the ionic radius increases
...
 

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●

Group 2 metals burn in oxygen to produce white metal oxides
...
 
Metal oxides and hydroxides also neutralise dilute acids to form salt and water
...
 
Compounds such as Mg(OH)​2​ are sparingly soluble
...
  

●

Thermal stability increases down group 2
...
 
The cation polarises the carbonate ion by attracting electrons towards itself
...
 
Large cations cause less distortion than small cations as they have a smaller charge 
density
...
  
This means Mg​2+​ ions will distort the carbonate ion the most, hence why MgCO​3​ has the 
lowest thermal stability of the group 2 carbonates
...
 
 
 
 
 

●
●

You can continue to ionise an element until no outer electrons remain
...
ionisation enthalpy
...
 

 
●

Factors affecting ionisation enthalpy: 
○ Atomic radius​ - The further the outer electrons are from the positively charged 
nucleus, the w
​ eaker the electrostatic attraction​ towards the nucleus,​ lowering 
ionisation enthalpy
...
The more 
protons in the nucleus, the ​greater the positive charge​
...
 
○ Electron shielding​ - The ​inner electron shells shield​ the outer electrons from the 
electrostatic forces from the nucleus
...
 

●

First ionisation enthalpies decrease down a group: 
○ Outer electrons are​ further from the nucleus​ as atomic radius increases, so 
electrostatic forces are weaker
...
 
○ Although nuclear charge increases due to a​ larger number of protons​, this 
factor is l​ ess important​, hence why the ionisation enthalpy ​does not increase 
down a 
group
...
 
○ All outer electrons in the same period are roughly on the same energy level, so 
atomic radius and electron shielding is virtually the same across an entire period
...
 
○ There are some small drops between the trends in the groups
...
This is because of the relatively low nuclear charge, so the electrostatic forces of 
attraction are weaker
...
 
P-block metals have a higher ionisation enthalpy compared to elements in the same 
period
...
  

 
 
 
 
 
 

 
 
 
 
 
 
 
 

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●

 
(s) the solubility of compounds formed between the following cations and anions: Li​+​, Na​+​, 
K​+​, Ca​2+​, Ba​2+​, Cu​2+​, Fe​2+​, Fe​3+​, Ag​+​, Pb​2+​, Zn​2+​, Al​3+​, NH​4​+​, CO​3​2–​, SO​4​2–​, Cl​–​, Br​–​, I​–​, OH​–​ , NO​3​–​; 
colours of any precipitates formed; use of these ions as tests e
...
Ba​2+​ as a test for SO​4​2–​; a 
sequence of tests leading to the identification of a salt containing the ions above 

 

●
●
●

Group 1​ and a
​ mmonium​ salts are ​soluble​
...
 
Halides​ are s​ oluble ​except: 
○ Silver halides (Cl is white ppt, Br is cream ppt, I is yellow ppt
...
I is yellow ppt
...
) 
 

●

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●
●
●
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Sulfates ​are s​ oluble ​except: 
○ Barium sulfate (white ppt
...
) 
○ Lead sulfate (white ppt
...
 
Silver carbonate is yellow ppt
...
 

 
Tests for ions 

 

Flame tests 
● Some metal cations give off a characteristic colour when heated
...
 
(This converts the sample to the metal chloride which is far more volatile and will 
combust readily)
...
 
 
Metal cation 

Flame colour 

Li​+ 

Bright red 

Na​+ 

Yellow 

K​+ 

Lilac 

Ca​2+ 

Brick red 

Ba​2+ 

Apple green 

Cu​2+ 

Blue-green 

  
 
Test for cations 
● Adding NaOH to the sample may produce an insoluble hydroxide with a characteristic 
colour
...
 

 
Test for anions 
● Add dilute HCl to the sample
...
 
 
 
 
● To identify sulfates, add dilute HCl (to get rid of traces of carbonate ions) followed by 
barium chloride solution
...
 
 
 
 
● Ammonia gas is alkaline, so you can test for its presence using damp red litmus paper
...
  
● To test for ammonium ions, add some sodium hydroxide in a test tube and gently heat
...
 
 
 
 
 
● To test for hydroxide ions, put a piece of red litmus paper into solution
...
Hydroxides are not the only alkaline substance, so it is 
best to eliminate all other possibilities
...
 

●

If a coloured silver halide ppt forms, a halide is present (Cl - white, Br - cream and I - 
yellow)
...
  
Aluminium reduces nitrate ions to ammonium ions
...
 
Damp red litmus paper will identify if ammonia gas has been produced, so the original 
sample must have contained nitrate ions
...
The acid should not contain ions you are testing for (e
...
do not use HCl when 
testing for chloride ions)
...
 
● Bases are insoluble substances with a pH greater than 7 and react by accepting protons 
(H​+​ ions) from other substances
...
 
● Acids and bases react together to form a salt and water in a neutralisation reaction
...
 
● Once the insoluble salt has precipitated out of solution, filter it from the solution and 
then wash with deionised water
...
  
● Place in a desiccator to cool
...
 
● Add the solid metal, metal oxide or metal hydroxide to the acid
...
The solution in neutralised after the solid stops reacting
...
 
● Filter off the excess solid to obtain the salt solution
...
This is crystallisation
...
 

●
 
Making soluble salts with an alkali 
● If you are using an alkali, you cannot use the above method as you do not know when 
the acid has been neutralised
...
Once known, repeat the titration, but do not add indicator as 
this will contaminate the salt
...
 
● Filter the mixture and wash solid residue with deionised water
...
 
● Remove solid at regular intervals and cool in desiccator before weighing
...
 
 
 
(v) the electromagnetic spectrum in order of increasing frequency and energy and 
decreasing wavelength: infrared, visible, ultraviolet  
● EM radiation is energy transferred as waves with a spectrum of different frequencies
...
 
 
Absorption spectra 
● When EM radiation is passed through a gaseous element, electrons only absorb specific 
frequencies corresponding to the difference in energy levels
...
 
 
 
 

Emission spectra 
● When an excited electron falls back to its ground state in an atom, energy in the form of 
EM radiation is released
...
 
 
● As the electronic configuration is unique for each element, each will have a characteristic 
absorption and emission spectrum
...
 
● For any particular element, the frequencies in an emission spectrum are the same as 
those missing in an absorption spectrum
...
 
 
 
 
 

 

(iii) the relationship between the energy emitted or absorbed and the frequency of the line 
produced in the spectra, ΔE =
​ ​ hν  
● When electrons move to a higher or lower energy level, it absorbs or emits EM radiation 
of a specific frequency

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