University:
University of Arkansas
Course:
CHEM 1053 | Chemistry in the Modern World
Academic year:

2023
Views:

140

Pages:

1
Author:

madeleinejames20

If you have a sample of a naturally occurring element, let's say neon, you'll have multiple isotopes in the sample. An isotope's natural abundance is the percentage by mass of that isotope in a naturally occurring sample of the element. For neon with a naturally occurring sample, you'll have approximately 90.48% of the isotope neon-20, 0.27% of the isotope neon-21, and 9.25% of the isotope neon-22 in the sample. The atomic mass of an element is the weighted average of its naturally occurring isotopes. Most periodic tables list the atomic mass for each element. So if you have a naturally occurring sample of an element, the atomic mass is the average mass for each atom. This will allow us to convert between mass and the number of atoms later on. We can experimentally determine the natural abundance of each isotope for an element using mass spectrometry. In mass spec, the sample is heated until it's vaporized — that is, turned into a gas. Those gaseous atoms are then ionized using an electron beam so they have a net charge. These ions are then accelerated using an electric field. The electric field causes a particular force on the ions. The larger the ion, or the more neutrons the isotope has, the less it will be accelerated. At the same time, smaller isotopes with fewer neutrons will be accelerated more with the same force. These ions are then passed through a perpendicular magnetic field. A charge moving through a perpendicular magnetic field experiences a force called the Lorentz force, which is perpendicular to both the magnetic field and direction of movement of the charge. This causes the ion to be deflected. Once again, heavier isotopes will be deflected less and lighter isotopes will be deflected more by the same force. When the ions are detected at the end, the natural abundance of each isotope can be calculated.