3.3.6.2 Mass spectrometry

• Define relative atomic mass

  The weighed mean mass of an atom of an element compared to 1/12th of an atoms of carbon-12
• Why does Cr have a greater boiling point than Br2 when it has more electrons?

  Cr is a giant metallics lattice, stronger electrostatic force of attraction between delocalised electrons and metal ions, Br is a simple molecular structure, weak IMF
• Why does Cr form compounds with a +6 oxidation state

  It has +6 left to fill a sub shell, energetically favourable
• Why is a K ion smaller than K atom

  Same nuclear charge, same number of protons, K ions has less electron repulsions between remaining electrons, lost the 4s sub shell
• What happens when a mass spectrum of a molecule is produced?

  The molecules in the sample are bombarded with electrons, which removes electrons from the sample, producing +ve ions which can be detected
• What happens when molecules in a sample is bombarded?

  Electrons are removed from the sample, producing +ve ions which can be detected
• What is a molecular ions?

  Organic molecule that is bombarded with electrons knocking an electron from the molecule producing a +ve ion
• Define fragmentation

  Molecular ions breaks apart into smaller fragments due to being unstable
• Why are small peaks sometimes seen above the molecular peak?

  Smaller peaks are caused by C-13 or CI-37 isotopes
• How to molecules break up more?

  At weak bonds, or bonds which rise to stable fragments
• What will have a higher commonality?

  Carbocations and alkyl groups containing C=O bonds
• Why is heating under reflux used in the synthesis of organic compounds?

  Heat may be applied to a reaction without the reactants or solvent escaping
• What can high resolution mass spectrometers do?

  Measure the precise m/z of any molecular ion
• Mass spectra revel the presence of

  Isotopes