Specification Point 1.17:
Be able to calculate the relative atomic mass of an element (Ar) from isotopic abundances
Calculating Relative Atomic Mass
Isotopes:
Atoms of the same element that contains the same number of protons and electrons but different number of neutrons.
Equation:
(% of isotope 1 x mass of isotope 1) + (% of isotope 2 x mass of isotope 2)
Ar = _______________________________________________________________
100
Example:
The table shows information about the isotopes in a sample of Rubidium
| Isotope | Number of protons | Number of neutrons | Percentage of isotope in sample |
|---|---|---|---|
| 1 | 37 | 48 | 72% |
| 2 | 37 | 50 | 28% |
Use information from the table to calculate the relative atomic mass of this sample of Rubidium. Give your answer to one decimal place.
( 72 x 85 ) + ( 28 x 87 )
____________________________ = 85.6
100
Relative atomic mass = 85.6
Author: Jamie
Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.