Relative formula mass

• What is meant by relative formula mass?

  It is the sum of atomic masses in a formula
• How is the relative atomic mass of an element determined?

  It is the average mass of isotopes weighted by abundance
• What does the term abundance refer to in isotopes?


  How common an isotope is
• What are the two main isotopes of chlorine?

  Chlorine-35 and Chlorine-37
• Why does chlorine have a relative atomic mass of 35.5?

  It is the weighted average of its isotopes
• What is the symbol for relative formula mass?

  It is represented by the symbol 'Mr'
• What are the two key facts about relative formula mass?

  It has no units and never involves big numbers
• How do you calculate the relative formula mass of methane (CH₄)?

  1 x 12 + 4 x 1 = 16
• What is the relative formula mass of methane?

  16
• What happens when a large number is placed in front of a formula?

  It indicates multiple molecules of that compound
• What is the relative formula mass of calcium sulfate (CaSO₄)?

  1 x 40 + 1 x 32 + 4 x 16 = 136
• What is the relative formula mass of calcium sulfate?

  136
• How do you calculate the relative formula mass of magnesium hydroxide (Mg(OH)₂)?

  1 x 24 + 2 x 16 + 2 x 1 = 58
• What is the relative formula mass of magnesium hydroxide?

  58
• Why is it important to remember that relative formula mass has no units?

  It simplifies calculations and comparisons
• What is the process for calculating relative formula mass?

  • Identify the formula of the compound
  • Find the relative atomic masses of each element
  • Multiply by the number of atoms in the formula
  • Sum all the values to get relative formula mass
• What types of questions can you expect in the workbook related to relative formula mass?

  • Calculating relative formula mass for various compounds
  • Identifying components of a given formula
  • Understanding the significance of relative formula mass