Relative Formula Mass"

• What should you be able to state by the end of the video?

  What's meant by relative formula mass
• What is the relative atomic mass of an element?

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

  How common an isotope is
• What is the atomic number of chlorine?

  17
• How many neutrons does the chlorine isotope with mass number 35 have?

  18 neutrons
• How many neutrons does the chlorine isotope with mass number 37 have?

  20 neutrons
• What is the average mass number of chlorine as seen on the periodic table?

  35.5
• Why is the mass number of chlorine 35.5?

  It is the weighted average of the isotopes based on their abundance
• What is the definition of relative formula mass?

  The sum of the relative atomic masses of the atoms in the numbers shown in the formula
• What symbol is used for relative formula mass?

  It has a specific symbol, often denoted as Mr
• What are the units for relative formula mass?

  Relative formula mass has no units
• Do calculations for relative formula mass involve large numbers?

  No, relative formula mass never involves big numbers
• How do you calculate the relative formula mass of methane?

  By adding the relative atomic masses of 1 carbon and 4 hydrogen atoms
• What is the relative atomic mass of carbon?

  12
• What is the relative atomic mass of hydrogen?

  1
• What is the relative formula mass of methane?

  16
• What happens when a large number is placed in front of a formula, like in 2CH₄?

  It indicates that there are two molecules of that compound
• What is the relative formula mass of calcium sulfate?

  136
• What is the relative atomic mass of calcium?

  40
• What is the relative atomic mass of oxygen?

  16
• What is the relative atomic mass of sulfur?

  32
• How do you calculate the relative formula mass of magnesium hydroxide?

  By adding the relative atomic masses of 1 magnesium, 2 oxygen, and 2 hydrogen atoms
• What is the relative formula mass of magnesium hydroxide?

  58
• What is a key point to remember about relative formula mass?

  It has no units
• What are the steps to calculate the relative formula mass of a compound?

  • Identify the number of each type of atom in the formula
  • Find the relative atomic mass of each atom
  • Multiply the atomic mass by the number of atoms
  • Sum all the values to get the relative formula mass
• What are some common compounds to calculate relative formula mass for?

  • Methane (CH₄)
  • Calcium sulfate (CaSO₄)
  • Magnesium hydroxide (Mg(OH)₂)