Relative Mass

Relative Atomic Mass

  • average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12 
  • Ar of each element is shown in periodic table 
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Relative Isotopic Mass

  • mas of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12
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Calculating Relative Atomic Mass

  • relative isotopic mass - usually whole number 
  • relative atomic mass - average so not whole number 
  • given percentage 
  • multiply % by isotopic mass & divide by the total % 
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Relative Molecular Mass

  • average mass of a molecule on a scale where an atom of carbon-12 is exactly 12
  • to find Mr, just add up relative atomic mass values of all the atoms in the molecule 
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Relative Formula Mass

  • average mass of a formula unit on a scale where an atom of carbon-12 is exactly 12
  • used for compounds that are ionic or giant covalent 
  • to find relative formula mass, just add up relative atomic masses of all ions in formula unit 
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