Revision notes for AQA AS Chemistry Unit 1- Atomic Structure

These are my revision notes for the first topic in AS CHEM. It summarises nicely everything you need to know and it these that I'll be using to revise for the exam in January.

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ATOMIC STRUCTURE
KEY DEFINITIONS
RELATIVE ATOMIC MASS-is the average mass of an atom taking in to account its isotopes
and their abundances compared to 1/12 of Carbon-12
RELATIVE ISOTOPIC MASS-is the mass of an isotope of an element compared to 1/12 of
Carbon-12
RELATIVE MOLECULAR MASS-is the average mass of a molecule compared to 1/12 of
Carbon-12
ISOTOPE-An isotope is an element with the same number of protons and electrons but a
different number of neutrons in the nucleus.
FIRST IONISATION ENERGY-is the energy required to remove 1 electron from each atom in
1 mole of gaseous atoms to form 1 mole of gaseous
NUCLEAR CHARGE-The more protons in the nucleus the more positively charged it will be
and the stronger attraction for the electrons
ELECTRON SHIELDING-as the number of electrons between the nucleus and the outer
electrons increases the attraction of outer electrons to nuclear charge decreases.
A HIGH IONISATION ENERGY MEANS A HIGH ATTRACTION BETWEEN ELECTRONS AND
NUCLEUS
Subatomic Particle Relative Mass Relative Charge
Proton 1 +1
Neutron 1 0
Electron 1/1850 -1

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IONISATION ENERGIES
{FIRST IONISATION ENERGY EQUATION}
[X(g) X+(g) + e-]
GOING DOWN A GROUP IN THE PERIODIC TABLE
There are more filled energy levels between the nucleus and the outermost electrons.
These filled energy levels shield the outer electrons from the attractive force of the
positive nucleus. As the radius of the atom increases, the distance between the nucleus
and the outer electron increases and therefore the force of attraction between the
nucleus and outer most electrons is reduced.…read more

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MASS SPECTROMETRY
This is the process of Vaporisation, Ionisation, Acceleration, Deflection and Detection.
It is important to note that this only works for gaseous samples so that is why it is vaporised
first. Only the process has to happen in a vacuum so that the ions don't react with particles in
the air. In ionisation all samples are made positive even the ones that don't really ionise like
Argon.…read more

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Molecular Mass with.
Working out Relative Atomic Mass and Relative Molecular Mass from a mass spectrum
Ar--STEP ONE
For each peak read the % relative isotopic abundance from the y-axis and the relative
isotopic mass from x-axis. Multiply them together to get the mass for each isotope.
STEP TWO
Add up these totals
STEP THREE
Divide by 100
Mr
With Relative Molecular Mass, it gives a peak in the spectrum with the highest mass
(furthest to the right) and this is labeled M.…read more

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Al 2 2, 2,1
6
14 Si 2 2, 2,2
6
15 P 2 2, 2,3
6
16 S 2 2, 2,4
6
17 Cl 2 2, 2,5
6
18 Ar 2 2, 2,6
6
19 K 2 2, 2,6,- 1
6
20 Ca 2 2, 2,6,- 2
6
21 Sc 2 2, 2,6,1 2
6
22 Ti 2 2, 2,6,2 2
6
23 V 2 2, 2,6,3 2
6
24 Cr 2 2, 2,6,5 1
6
25 Mn 2 2, 2,6,5 2
6
26…read more

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With regards to ions:
If it is a two plus ion it means that it has lost two electrons and electron configurations should show
this.
EG O2+
1S2 2S2 2P2
If it is a two negative ion it means that it has gained two electrons and electron configurations should
show this.
EG O2-
1S2 2S2 2P6
HOWEVER
You have to be weary because electrons are taken from the lowest energy levels which means...…read more

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ATOMIC MODELS
The first model was done by john Dalton who described atoms as solid spheres and said that the
different spheres were the different elements. This was called the solid indivisible sphere model.
The next model was made by JJ Thompson in 1897 who concluded that atoms weren't solid and
indivisible. His measurements of charge and mass showed that an atom must contain even smaller,
negatively charged particles-electrons. The solid sphere idea of the structure had to change.…read more

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