Atoms with the same number of PROTONS but different number of NEUTRONS
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What is the Mass Spectrometer used for?
To determine all isotopes present in a sample of an element, therefore identify elements
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Why does the Mass Spectrometer be under a vacuum?
to prevent air particles being ionised and registered by the detector
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What are the 4 steps in a mass spectrometer?
1. Ionisation - Electron impact OR Electrospray 2. Acceleration 3. Flight tube 4. Detection
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How is the sample ionised in Electron Impact?
Vaporised sample is injected at low pressure -> electron gun fires high energy electrons at the sample, knocking outer electron -> forms positive ions Ti -> Ti+ + e-
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How does Electrospray ionisation work?
1) sample is dissolved in volatile solvent 2) injected through needle giving fine mist 3) tip of the needle has high voltage 4) Sample molecule gains a proton (H+) 5) solvent evaporates away while the ions move towards the negative plate
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What happens at Acceleration?
Ions are accelerated by an electric field. Assume ions have the same kinetic energy, therefore velocity depends on the mass. heavier = slower
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What happens at the Flight Tube?
1) lighter ions are faster therefore move faster at the drift area. 2) ions are distinguished by flight times t=d/v
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What happens at the detector?
1) ions reach the detector and generate small current, which is fed to the computer for analysis 2) size of the current is proportional to the abundance of the species
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How do you calculate the R.A.M?
sum of (isotopic mass X % abundance) / 100
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What is the largest m/z peak equal to?
relative molecular mass
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What is the largest m/z peak called?
Parent ion / Molecular ion
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Which ionisation causes fragmentation?
Electron impact ionisation
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what are the sub energy levels and how many electrons can they hold?
s - 2, p - 6, d - 10, f - 14
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give the electronic configuration of Chromium
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
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give the electronic configuration of Copper
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
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when forming ions, which shell is lost first? 4s or 3d?
4s
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Define First IE
the energy required to remove one mole of gaseous electrons to form one mole of gaseous ions
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what are the factors that affect IE?
1) nuclear charge 2) distance between electron from the nucleus 3) Shielding
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why does He have the largest first IE?
its electron in the first shell closest to the nucleus has no shielding from inner shells. He has 1 more proton than H
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why does 1st IE decrease down the group?
outer electrons are further away from the nucleus, therefore more shielding, hence lower attraction to the nucleus
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why is there a general increase in 1st IE across a period?
more electrons in the same shell, same distance from nucleus and same shielding effect. number of protons increase, so nucleus attraction is greater
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Why has Na a much lower first ionisation energy than Neon?
Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. So Na’s outer electron is easier to remove and has a lower ionisation energy.
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Why is there a small drop from Mg to Al?
Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell. The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s elect
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Why is there a small drop from P to S?
With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital. When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes
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Other cards in this set
Card 2
Front
What is the Mass Spectrometer used for?
Back
To determine all isotopes present in a sample of an element, therefore identify elements
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