atomic structure

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what is the relative mass of a proton, neutron and electron
proton=1 neurton=1 electron=1/1840
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what is the definition of an isotope?
isotopes are atoms with the same number of protons but different number of electrons
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name the 4 stages of TOF mass spectrometer
1. ionisation (electron impact or electro spray ionisation) 2. acceleration 3. flight tube 4. detection
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what is the mass spectrometer used for?
is it used to determined all the isotopes present in a smaple of an element and to identify an element
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describe electron impact ionisation
-vaporised sample is injected at low pressure-an electron gun fires high energy eletrons at sample-this knocks out an outer electron-forming positive ions with different charge
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when is electon impact ionisation used and what can it cause?
it is used for elements and substances with a low formular mass but it can cause fragmentation
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describe electro spray ionisation
sample is dissolved in a volatile polar solvent-injected through a hypodermic needle with a high voltage tip giving a aerosole and gaining a proton from the solvent-solevent evaporates and ions move to negative plate
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when is elctrospray ionisation used
for larger organic molecule, the softer conditions of this technique mean fragmentation does not occur
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describe acceleration in TOF
positive ions accelerated by an electric field- KE=0.5xMxV^2-KE=kinetic energy (j) M= mass of particle (kg) V= velocity of particle (ms^-1)
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describe Flight tube stage of TOF
the positive ions with the different m/z values all hvae the same KE heavier particles take longer to move through the drift area, the ions are distinguisged by different flght times- T=d/V-T=time of flight d=length of flight tube v=velocity
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describe detection of TOF
the ions reached the detector and generate a small current, fed to a computer for analysis, current produced by electrons transferring from detector to positive ions size of the current is proportional to the abundance of the species.
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equation for relative taomic mass using %abundance
sum of (isotopic mass x %abundance)/100
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calculate relative atomic mass using relative abundance
sum of(isotopic mass x relativ abundance)/total relative abundance
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how do you measure the Mr of a molecule using TOF which has used electron impact ionisation
fragmentation will occur, gives a series of peaks, the peak with the largest m/z value will be due to the complete molecule and will be equal to its Mr (as long as its charge is +1) this peak is called the molecular ion
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how do you measure the Mr of a molecule using TOF which has used Electro spray ionisation?
fragmentation wont occur, on peak equal to the mass of the MH+ ion. so subtract 1 to get the Mr of the molecule (H+ hass a mass of 1)
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define the first ionisation energy
the first ionisation energy is the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
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define the second ionisation energy
the second ionisation energy is the enthalpy chnage when
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Other cards in this set

Card 2

Front

what is the definition of an isotope?

Back

isotopes are atoms with the same number of protons but different number of electrons

Card 3

Front

name the 4 stages of TOF mass spectrometer

Back

Preview of the front of card 3

Card 4

Front

what is the mass spectrometer used for?

Back

Preview of the front of card 4

Card 5

Front

describe electron impact ionisation

Back

Preview of the front of card 5
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