Lesson 5: Isotopes

isotope

is an atom that has the same number of protons and a different number of neutrons. The atom is still considered the same element (still contains the same number of protons) as before but will have a different mass. The change in mass may change the atom’s properties.

1 st Isotope Notation:

One way is to write the element name followed by the number of neutrons and protons added together. The number of protons plus neutrons also equals the mass number.

2nd:

A second notation for isotopes is to write it as the element symbol with the mass number on the upper left side and the number of protons on the bottom left side. For carbon, the notation would be for carbon-12 and for carbon-13.

Hydrogen

has three main isotopes. These are protium, deuterium and tritium. Protium is 'H or hydrogen-1. Protium accounts for 99.98% of all hydrogen atoms. Deuterium (?H) and tritium (*H) comprise the last 0.02%. There are other isotopes, but these are all manmade.

One primary use of deuterium (hydrogen-2) is nuclear magnetic resonance spectroscopy (NMR spectroscopy) for solvents. The NMR measures hydrogen-1, so solvents that dissolve the sample of interest only have hydrogen-2. By using hydrogen-2 in the solvent, the spectrum generated does not measure the spectrum of the solvent.

Carbon

has 15 known isotopes with various half-lives. The longest half-life is carbon-14. Carbon-14 is

commonly used for radiometric dating. This technique allows for the approximation of the age of a sample

based on the amount of carbon-14 present.

The other natural isotopes of carbon are carbon-12 and carbon-13. The other known isotopes are all human-

made.