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Video transcript

in other videos we have talked about the idea that even for a given element you might have different versions of that element and we call those different versions isotopes and each isotope of an element can have a different atomic mass and that stems from the idea that if it's a given element it's going to have the same number of protons but you could have a different number of neutrons now one question that you might have been asking yourself is how have chemists been able to figure out what the various isotopes of an element are and their relative abundance what percentage of an element that we find in the universe is of isotope a versus say isotope B and the answer to your question is they use a technique known as mass spectrometry I can never say it right mass spectrometry sometimes you'll hear the word mass spectroscopy and they're essentially referring to the same idea and what this technique is is that you put a little bit of a sample right over here let's say we're talking about zirconium in this example and you heat it up so you have it you have a bunch of the zirconium floating around and then you beam it you will bombard it with a bunch of electrons and what the electron bombardment does is it can knock off electrons from the atoms in your sample and it can I anice them and by ionizing some of your atoms they now have charge and because they have charge they can be accelerated through these electric plates so now you have these ions in this case of zirconium moving quite rapidly through this chamber and then they enter into a magnetic field and a magnetic field a strong magnetic field can bend the path can deflect ions with charge for a given charge the force of the deflection will be the same but if you have a larger mass you're going to be deflected less and if you have a lower mass we're going to be deflected more and so what you see here are the different isotopes being deflected different amounts as they go through the magnetic field and then you have the detector and at different points of the detector you will detect each of these isotopes and the more ions that hit a certain part of the detector that means that hey I have more of that type of isotope in nature and then from that you can generate a chart that looks like this where you see on the horizontal axis sometimes you will see it labeled atomic mass and here it's in unified atomic mass units and you can see when you put the zirconium through the mass spectrometer like this you get a little bit that has a mass number of 96 you have a little bit more that it's a mass number of 94 92 91 and most of the zirconium over 50 percent has a mass number of 90 now in other cases you won't see it just in terms of atomic mass given a unified atomic mass units sometimes in this horizontal axis they'll give it in terms of mass to charge ratio where mass is the mass but then charge is essentially the charge of the ions now in a case where your charge is 1 for example if you knock one electron off of the atoms and you have a plus 1 charge well then the mass to charge ratio would be the same thing as atomic mass measured in unified atomic mass units if your ions have a different charge well then you would have to make the appropriate adjustment but an introductory chemistry class most of the time you will get things in terms of just straight-up atomic mass if you happen to get something in terms of mass to charge just to make sure that if the charge is say plus 2 that you make the appropriate adjustment for the masses but this right over here will tell you the various isotopes and it will tell you its abundance and it all comes from this process of ionizing those atoms speeding them up deflecting them through a magnetic field and the ions that have a higher mass to charge ratio will be deflected less and the ions that have a lower mass to charge ratio will be deflected more and you can use that information to make a graph like this
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