Relative Formula Mass

• Relative formula mass is the Mr
• The relative atomic mass of an element is the average mass of the isotopes of that element weighted to take into account the abundance of each isotope.
• The relative formula mass of a compound is the sum of the relative atomic masses of the atoms shown in the formula.
• Relative formula mass has no units
• Relative formula mass never involves big numbers
• Methane - CH4

  • Carbon Ar = 12
  • Hydrogen Ar = 1
  • 12 x 1
  • 4 x 1
  • Mr of methane is 16
• We do not use big numbers to calculate relative formula mass, so CH4 is the same as $2CH_4$