Relative atomic mass

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

  Relative atomic mass
• What are isotopes?

  Atoms of the same element with different numbers of neutrons
• What is the atomic number of chlorine isotopes?

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

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

  20 neutrons
• What is the mass number for chlorine as shown on the periodic table?

  35.5
• How is the relative atomic mass calculated for an element with isotopes?

  It is a weighted average of the mass numbers based on the abundance of each isotope
• What does the term "abundance" refer to in the context of isotopes?

  How common each isotope is
• Why is the relative atomic mass of chlorine closer to 35 than to 37?

  Because the isotope with mass number 35 is three times more abundant than the one with mass number 37
• What is the formula to calculate relative atomic mass?

  The formula is \frac{(mass\ number\ of\ isotope\ 1 \times percent\ abundance\ of\ isotope\ 1) + (mass\ number\ of\ isotope\ 2 \times percent\ abundance\ of\ isotope\ 2)}{100}
• What is the relative atomic mass of boron if its isotopes have mass numbers of 10 and 11 with abundances of 20% and 80% respectively?

  10.8
• How is the relative atomic mass of boron rounded in the periodic table?

  It is rounded up to 11
• What are the mass numbers and abundances of the isotopes of magnesium?

  Isotope 1: mass number 24, 79%; Isotope 2: mass number 25, 10%; Isotope 3: mass number 26, 11%
• How is the relative atomic mass of magnesium rounded in the periodic table?

  It is rounded down to 24
• What is the relative atomic mass of magnesium based on its isotopes?

  24.3
• What is the process for calculating relative atomic mass using isotopes?

  1. Identify the mass numbers and abundances of the isotopes.
  2. Use the formula:

  \frac{(mass\ number\ of\ isotope\ 1 \times percent\ abundance\ of\ isotope\ 1) + (mass\ number\ of\ isotope\ 2 \times percent\ abundance\ of\ isotope\ 2)}{100}

  1. Calculate the weighted average.
• What are the steps to calculate the relative atomic mass of an element with multiple isotopes?

  • Gather mass numbers and percent abundances of each isotope.
  • Apply the formula for relative atomic mass.
  • Round the final result as per periodic table conventions.