AQA Chemistry, Unit 1, Atomic Structure

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Unit 1 ­ Atomic Structure
Fundamental Particles ­ Protons, Electrons and Neutrons
Isotopes- atoms of the same element that contain a different number of neutrons.
Different isotopes of the same element react identically, as they have the same number of protons
and neutrons, but different mass numbers due to different amount of neutrons in the nucleus.
Nucleons are responsible for almost all of the mass of an atom, because electrons weigh 1/1840
(virtually nothing).
Particle Position Relative Charge Relative Mass
Proton nucleus 1+ 1
Neutron nucleus 0 1
Electron electron shells 1- 1/1840
We use the relative mass because the real masses are incredibly small, so it's easier to work out
using relative charge.
Mass Number ­ Number of protons and neutrons in the atom
Atomic Mass ­ Number of protons in the nucleus.
One mole of any gas at room temperature and pressure (rtp) occupies a volume of 24dm3. This
is called the molar volume
Mass Spectrometry
Step One: Vaporisation - The sample must be in the vapour state to travel through the machine
Step Two: Ionisation - Via and electron gun, 1+ and occasionally 2+ ions are formed, because the
electrons are fired at the atoms at a high speed and so they knock the electrons off the atoms to
form the ions.
Step Three: Acceleration - Via an electric field
Step Four: Deflection - Via a magnetic field ­ the amount by which they are deflected depends on
the mass-to-charge ration; m/z.
Step Five: Detection - The strength of the magnetic field is increased slowly to detect ions of
increasing mass. When ions strike the collector they induce a current, which is amplified and
converted into a mass spectrum. The more ions of a particular m/z the greater the current and the
larger the peak.
Ionisation Energy
First ionisation energy is the energy required to remove one electron from each atom in one
more of gaseous atoms.

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Unit 1 ­ Atomic Structure
Na(g) e- + Na+(g)
The second ionisation energy is the energy required to remove the second electron (not both
electrons):
First: Na(g) e- +Na+(g)
Second Na+(g) e- +Na2+(g)
Factors affecting ionisation energy
Atomic radius
The further the outer electron from the nucleus, the less energy required to remove it
Nuclear charge
The more protons, the more energy it takes to remove the outer electron
Shielding
More inner shells, more shielding, easier to remove outer electron
Evidence for electron arrangement (from…read more

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Unit 1 ­ Atomic Structure
1 1s 2
2 2s2p 8
3 3s3p3d 18
4 4s4p4d4f 32
Electrons fill orbitals from the lowest energy upwards.…read more

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