Relative Atomic Mass Flashcards

All 4 cards in this deck

What is the relative atomic mass of an element?

An average value that takes account of the abundance of the isotopes of the element.

What are the steps to calculate relative atomic mass from percentage abundances?
e.g. chlorine: 75% of mass number 35, 25% of mass number 37

1. Multiply each mass number by its percentage abundance: $35 \times 75 = 2625$ and $37 \times 25 = 925$.
2. Add the results: $2625 + 925 = 3550$.
3. Divide by 100: $A_r = 35.5$.

True or false? Relative atomic masses are always whole numbers.

False. They are averages over the isotopes, so they are often not whole numbers.

Which number of each isotope is used in a relative atomic mass calculation — the mass number or the atomic number?

The mass number, multiplied by that isotope's percentage abundance.