Atoms - key concepts

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Protons have a mass of 1 annd a charge of +1       

Electrons have a negligable mass and a charge of -1                                          

Neutrons have a mass of 1 and a charge of 0

Mass number = Protons + Neutrons                                                                  

Atomic number = Protons                                                                                

Number of electrons = Number of Protons

Protons and neutrons are contained in the nucleus                                            

Electrons are in shells around the nucleus

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

Average atomic mass = average mass of 1 mole of an element / 1/12 mass of an atom of Carbon 12

Mass Spectrometry - a technique used to analyse atoms and molecules according to their masses. It is used to detect and measure the relative abundances of isotopes

Ionisation - an e- gun fires a beam of high energy e- at a vapourised sample knocking off e- so the atoms or molecules become mostly positive ions with a +1 charge       

  X(g) + e- ---> X+(g) + 2e-

Acceleration - charged plates produce an electric field which attracts positive ions causing them to accelerate down a tube. Holes in the plates allow some ions to pass through forming a beam of positive ions

Deflection - a magnetic field at bend in the tube deflects the ions of a specific mass/charge ratio (m/z) will hit the detector at the end of the tube and produce an output to a recorder. Heavier ions need a strong…


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