AQA AS Chemistry - Unit 1

Foundation Chemistry

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                      Mass               Charge                                                                            Proton              1                      +1                                                               Electron      negligable               - 1                                                                    Neutron            1                       0                          

Mass Number = protons + neutrons                                                                           Atomic Number = number of protons

Protons and Neutrons are contained in the nucleus whilst Electrons are contained in shells around the nucleus

Isotopes are atoms with the same atomic number but a different mass number

Ar = average mass of 1 mole of an element                                                                           1/2th mass of an atom of carbon 12 

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Mass Spectrometry

Technique used to detect and measure relative abundances of isotopes

Ionisation - e- gun fires a beam of high energy e- at a vapourised sample knocking off an e- and making the particles +ive ions mostly with a +1 charge

Acceleration - plates produce an electric field attracting +ive ions accelerating them along tube. Holes in plates allow some ions through forming beam of +ive ions                                                                                                                      Deflection - a magnetic field at bend of tube deflects the ions of a specific m/z ratio so they hit the detector at end of tube producing an output to a recorder. Heavier ions need a stronger magnetic field to deflect them enough to hit detector                                                                                                                       Detection - field strength gradually increased so ions of a progressively greater mass hit detector. Intensity is proportional to number of ions present in sample of that mass. A vacuum pump is attatched to remove air from inside so ions dont collide with air molecules

Average atomic = sum of (mass x peak) values                                                                                          sum of peak heights

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Steph Underwood


it says 1/2th of carbon 12...think its meant to say 1/12 carbon 12 x

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