3.1.2.1 Relative atomic mass and relative molecular mass

• What does relative atomic mass mean?

  The relative atomic mass, Ar , is the average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12
• What does relative molecular mass mean?

  The relative molecular mass, Mr , is the average mass of a molecule on a scale where an atom of carbon-12 is exactly 12.

  To find the Mr , just add up the relative atomic mass values of all the atoms in the molecule.
• What does relative isotopic mass mean?

  Relative isotopic mass is the mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12.
• How to calculate relative atomic mass?


  Sum of (mass of each isotope x abundance) divided by 100.
• What is the relative formula mass?


  Relative formula mass is the average mass of a formula unit on a scale where an atom of carbon-12 is exactly 12. Used for compounds that are ionic/ giant covalent