Interpreting Mass Spectra
- Isotopes are different atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
- These are atoms of the same elements but with different mass numbers
- Therefore, the mass of an element is given as relative atomic mass (Ar) by using the average mass of the isotopes
- The relative atomic mass of an element can be calculated by using the relative abundance values
Ar =
-
- The relative abundance of an isotope is either given or can be read off the mass spectrum
Worked example
Calculating relative atomic mass of oxygen
A sample of oxygen contains the following isotopes:What is the relative atomic mass, Ar, of oxygen in this sample, to 2dp?
Answer
-
- Ar =
- Ar = 16.0044
- Ar = 16.00
Worked example
Calculating relative atomic mass of boron
Calculate the relative atomic mass of boron using its mass spectrum, to 1dp:
Answer
-
- Ar =
Examiner Tip
You can be expected to work with tables or graphs of data to calculate relative atomic mass
You can also be expected to do these calculations backwards to determine the abundance of one isotope given sufficient information