atomic structure past paper questions Flashcards
write the equation for the first ionisation energy for Rb
Rb(g) - Rb(g)+ + e-
always remember the gas state symbol as ionisation occurs when atoms are in a gaseous state
Kr has an isotope with the relative atomic mass of 42 explain why
the 84 isotope has 2 electrons knocked off
sometimes two electrons may be removed from a particle forming a 2+ ion
e.g. 24 Mg2+ with a 2+ charge would have a m/z of 121
state one change in the operation of the mass spectrometer that will change the path of the ion
changing the electromagnet/ electric field
explain how the detector in a mass spectrometer enables the abundance to be measured
ions hit the detector and cause a current
the current is proportional to the abundance (of the isotope_
compound Q is analysed in time of slight mass spectrometer. A sample compound Q in solution is injected into the mass spectrometer at high pressure
A high voltage is the applied to remove electrons from atoms of the sample
Give the name of this process
electrospray IONISATION
explain how a time of flight mass spectrometer separates charged particles with different mass/charge ratios
the ions are accelerated to CONSTANT kinetic energy (1 mark) by an ELECTRIC FIELD (1 mark)
lighter ions are accelerated more than heavier ones ( 1 mark)
so ions with different masses take different amounts of time to travel through the mass spectrometer and reach the detector
use your understanding of the electronic structure of aluminium, silicon and phosphorus to explain your answer to question 3.4
aluminum, silicon, and phosphorus all have their outer electron in the same 3p subshell (1 mark)
so the shielding effect and the distance between the nucleus and the outer electron is the same/ very similar for all three elements
but the nuclear charge of silicon is higher than aluminum but lower than phosphors.
so the energy needed to remove the outer electron/ first ionisation energy of silicon should be greater than aluminium but lower than phossporus
give the full eloectron configuration of copper and explain why it deviates from the normal rules of electron configuration
1s2 2s2 2p6 3s2 3p6 3d10 4s1
copper donates one of its 4s electrons to the 3d sub shell to make a more stable 3d sub shell
remember for transition metals, the 3d sub shell fills up first then the 4s orbital fills up
( look at the textbook for reference)
there is a large jump in the trend of the successive ionisation energies of element X between the removal of the eighth and ninth electrons
Use your understanding of the factors that affect ionisation energy to explain why this is the case
(element X being neon)
the eighth electron is being removed from the second electron shell but the ninth electron is being removed from the first electron shell
The ninth electron is much closer to the nucleus than the eighth and experiences less shielding so it takes more energy to remove it
explain electronspray
sample is dissolved
injected through a needle at high voltage which is positively charged
each particle gains a proton
explain how first and successive ionisation energies in Period 3 (Na–Ar) and in Group 2 (Be–Ba) give evidence for electron configuration in sub-shells and in shells
this is giving reference on how some sub- shells have paired electrons and some do not
what is the relative atomic mass
average mass of 1 atom/ 1/2 of the MASS of C-12 ATOM
In addition to the major peaks at m/z = 63 and 65, much smaller peaks at m/z = 31.5
and 32.5 are also present in the mass spectrum. Identify the ion responsible for the
peak at m/z = 31.5 in the mass spectrum. Explain why your chosen ion has this m/z
value and suggest one reason why this peak is very small
Identity of the ION: 63Cu 2+
Explanation for m/z value:
63/2 = 31.5
the reason why this peak is very small:
more energy is needed to remove the 2nd electrons
how are the ions detected
POSITIVE ions collide with detector
causing the current to flow
why must the atoms be ionised
ONLY IONS can be accelerated by in electric field
what are some top tips for relative atomic mass
make sure you add up the bottom number when working out the relative atomic mass
always to 1.d.p
One of the isotopes of Ge, given in the table in part (c), has an ion that forms a small
peak in the mass spectrum which is indistinguishable from a peak produced by 36S+
ions.
Identify the ion and explain why
- identity of the ion: 72 Ge 2+
Same m/z as 36S+
what is the definition of isotope
atoms with the same number of protons but different number of neutrons
what is the definition of relative isotopic abundance
the percentage of different types of atom
present in the natural isotopic mixture
how are the ions distinguished by
the different flight times
describe acceleration
Positive ions are accelerated by an electric field
to a constant kinetic energy
why do we use electrospray for larger molecules
electrospray ionisation is used for larger organic molecules
This is because the “softer” conditions of this technique mean that FRAGMENTATION DOES NOT OCCUR
what happens when a molecule is put through with an electron impact ionisation instead of electrospray e.g. C4H10
it will often break up and give a series of peaks caused by the fragements
The peak with the larges m/z, however will be die to the complete molecule and will ve equal to the relative molecular mass,Mr, of the molecule
This peak is called the parent ion or molecular ion
what do we have to do if a molecule is put through a mass spectrometer with electrospray ionization
As fragmentation will not occur
There will be one peak that is equal to the mass of the MH+ ion
It will therefore be necessary to subtract 1 to get the Mr of the molecule. This is because with electrospray ionisation the molecular ion gains a proton
so if there was a peak that was 521.1 dor the MH+, the relative molecular mass of the molecule is 520.1
what is ionic drift
the stages of the mass spectrometer is
- vaporisation
the sample must be vaporised so that it can travel through the TOF - ionisation
- acceleration
4.ION DRIFT
particles travel through (the flight tube) with a constant speed and kinetic energy. They drift through and particles with a lower mass/charge ratio will travel faster
- ions are detected as electrical current and is made when particles hit the plate. Particles with lower m/z reach the detector first as they travel faster
stock definition for the relative atomic mass
the mass of an atom of an element measured on a scale which the mass of an atom of 12C is exactly 12
