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Summary AS AQA Chemistry 3.3.1 Atomic Chemistry notes
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Atomic Structure● The universe is made up of atoms.
● Atomic number = number of protons
● Mass number = total number of protons and neutrons
● Isotopes are atoms with the same number of protons but different number of
neutrons
● Relative atomic mass - average mass of 1 atom / 1/12 mass of Carbon 12
● Relative isotope mass - mass of 1 atom / 1/12 mass of carbon 12
● Relative molecular mass - sum of RAMs of all atoms in molecule / 1/12 mass of
carbon 12
Mass Spectrometer
● A sample is dissolved in a volatile solvent and is forced through a fine hollow
needle that is connected to the positive terminal of a high voltage supply.
● Producing droplets of positively charged ions.
● The solvent evaporates into the vacuum until a single positive charge ion
remains.
● The +ion is then passed through a flight tube.
● The +ion then hits a detector which records the time taken to travel down
the flight tube, as lighter positively charged ions will travel faster than
heavier ions.
● Stage 1: electrospray Ionisation - the sample to be ionised is dissolved in a
volatile polar solvent and is then forced through a fine hollow needle that is
connected to the positive terminal of a high voltage supply. The solvent acts as a
source of H+ ions.
M + H+ → MH+
This produces droplets of positively charged ions. The droplets of the solvent
then evaporate into the vacuum if the mass spectrometer
Another way of ionising a sample is by electron bombardment from an electron
gun. The gun fires electrons at the sample which knock off electrons from the
sample to create positive ions.
X(g) + e- → X+(g) + 2e-
● Stage 2 : Acceleration - The positively charged ions are accelerated by an
electrical field (negatively charged plates). This produces ions that all have the
, same kinetic energy. Lighter ions/ more positively charged ions achieve a higher
velocity.
KE=½mv2
● Stage 3 : ion drift - The ions pass through a hole in a negatively charged plate
forming a beam. They drift down a tube called a flight tube where there is no
electrical field (so they travel at the velocity they reached in the electric
field) to the detector.
2𝐾𝐸
v= 𝑚
● Stage 4 : Detection - The beam of ions passing through the machine is detected
electronically. The ions hit the detector and generate an electric current, as
electrons transfer from the detector to the positively charged ions. The more
ions that hit the detector the bigger the current
● When analysing an element the mass spectrometer produces a printout showing
the relative/charge ratio of what ever entered the detector
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