Contains the full lesson along with a supporting toolkit, including teachers’ notes.
What is a mass spectrometer?
The mass spectrometer is an instrument widely used by chemists, geologists, biologists, physicists and forensic scientists to determine the relative molecular mass of atoms and molecules. The spectrometer was invented in 1919 by Francis W Aston while working in the world famous Cavendish Laboratories in Cambridge under JJ Thompson, the man who discovered the electron.
What is relative molecular mass?
The relative molecular mass of a substance is defined as the sum of the relative atomic masses of the atoms in a molecule. However, not all atoms of a particular element have the same mass. Such atoms are called isotopes.
Frederick Soddy coined the phrase isotope while working with lead 206, 207 and 208 which are formed when uranium decays radioactively. He found that atoms of the same element can have the same number of protons but different numbers of neutrons.
Isotopes have the same number of protons therefore the sameAtomic Number. However, they have different numbers ofneutrons and therefore have different Mass Numbers. He was awarded the Nobel Prize in 1921 for this work.
Aston initially worked with neon. Using his mass spectrometer, he was eventually able to show that almost all elements haveisotopes. In fact, he used the mass spectrometer to discover 212 of the 278 naturally occurring isotopes or nuclides. He was awarded the Nobel Prize for his work in 1922.