S1, Ep 11: How (nuclear) isotopes are used

Caroline Christian, Ph.D.

What is an isotope? Isotopes are atoms that have the same number of protons (hence they are the same type of atom) but different numbers of neutrons. Wait what are protons and neutrons again? Protons, which are positively charged, and neutrons, which are neutral, are both contained in an atom's nucleus - or the center of the atom. Number of protons determines what kind of atom it is, for example all hydrogen atoms have one proton and it has a 1 above its symbol denoting this.

Number of neutrons is what determines which isotope you are looking at, for example, there are three isotopes of hydrogen: hydrogen-1, hydrogen-2, and hydrogen-3. The 1, 2, and 3 after the word hydrogen represents the mass number of the atom or the sum of an atom's protons and neutrons. So therefore, hydrogen-1 has 1 proton and 0 neutrons, hydrogen-2 has 1 proton and 1 neutron, and hydrogen-3 has 1 proton and 2 neutrons.

Why are isotopes important? They are important because they determine the atomic mass of an element. Atomic mass is the number that is below the symbol in the periodic table up above, for hydrogen it is 1.008. This is an average of the atomic masses of the different hydrogen isotopes with their abundance on the earth taken into account. So here is a question for you - if hydrogen's atomic mass is 1.008, which isotope of hydrogen is the most abundant on earth? Hydrogen-1, you guessed it!

Another purpose to mention isotopes is because lots of them are radioactive. For example, there are three isotopes of carbon: carbon-12, carbon-13, and carbon-14. Carbon-12 and carbon-13 are stable isotopes of carbon, whereas carbon-14 is unstable. It is radioactive and will decay (emit beta particles) to be transformed into a nitrogen atom. 14C --> 14N + beta-. Carbon-14 is also used for radiometric dating. Here is a good video that describes radioactive dating with Carbon-14. Next time we will consider how to use these radioactive isotopes and introduce a new term, half-life.

03/23/2018