Atomic masses

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  • Created by: sisi
  • Created on: 15-03-13 18:41
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  • Atomic Masses
    • Relative Isotopic mass
      • is the mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12
      • All the atoms in a single isotope are identical. They all have the  same mass measured against carbon 12
      • For an isotope, the relative isotopic mass is the same as the mass number
    • Relative atomic mass
      • Is the weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon -12
      • Most elements contain a mixture of isotopes each in different amount and with a different mass.
        • The contribution made by an isotope to the overall mass depends on
          • the percentage abundance of the isotope
          • the relative mass of the isotope
    • Relative molecular mass
      • is the weighted mean mass of a molecule with 1/12th of the mass of an atom of carbon-12
      • Many elements and compounds are made up of simple molecules such as O2 and CO2
    • Relative formula mass
      • is the weighted mean mass of a formula unit compared with 1/12th of the mass of an atom of carbon-12
      • Compounds with giant structure do not exists as simple molecules for example NaCl
    • Relative masses
      • Atomic masses are measured in U(unified atomic mass unit)
      • So the mass of 1/12th of an atom of carbon-12 is 1u

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