here we're going to talk about something called percent abundance and when we're working with an isotope say a sample of an isotope so let's say um I have just a box um of some element here um and we'll just say that this is uh maybe we'll just say this is boron um so I have a sample of boron and in this sample of boron maybe we have a couple of different isotopes so I'll say that this would be um one of the Isotopes of boron and then I could use a different color so this would be the other isotope um of boron so percent abundance is just going to tell us that if I have a giant sample or small sample if I have just a sample of any particular element it's going to tell me what percent of all of those atoms are each of the Isotopes so for this picture I drew so maybe we'll say that like the blue ones I have here are 80% and then the red one on are uh are 20% so the percent abundance just says you have this big sample of all these different isotopes of a given element how much of each one do you have basically so and it's presented as a a percentage so the way that we can figure this out um is to use a tool called a mass spectrometer um and so this is a analytical technique so I'm going to write that out here Mass spectroscopy so this is an analytical tool that allows us to differentiate um particles based on their charge to mass ratio so the way it works we have something that has a a basic setup like this where we're going to send a sample of gas into a chamber and there are a couple of different uh sections of this chamber so we're going to send our sample gas in and then here in this first region we're going to hit that sample of gas with an electron beam and that's basically going to dislodge some electrons so in this first section we're going to form cat ions we're going to form positive ions in here so if we send our sample in electrons are going to get dislodged and if we lose electrons we're going to form a positively charged ion so we're going to have a positively charged particle then we're going to go through the to the second section and in the second section here I'll just label this one as two so this is just a section where we're going to accelerate so we've created these uh positively charged particles or ions and we're going to now speed them up so we want them to to go really fast and then we're going to send them through this magnetic field and when we send them through the magnetic field it's essentially going to create a force that's going to deflect those positively charged particles based on their charged Mass ratio so the the particles that are bigger um are going to get deflected less and the particles that are smaller are going to get deflected more and a way um I think could' be helpful to kind of think about how that works or why that works um is if we think about if you go bowling so if we go bowling here's like my little bowling alley right we have all our pins um if we take a big giant bowling ball and we send it straight down the bowling alley um it's going to go down in it would hit the pins right if we take the same setup so here's again my bowling alley here's all the pins at the end if I take a much smaller uh ball let's say like a pingpong ball or something something that's a lot less massive but I send it down with the same speed um it would also go down and it would hit the pins but probably not knock them over right but what we're interested in is this speed so if I start both of these things the the big bowling ball here here and then the small pingpong ball here and I send them straight down the bowling alley but now I'm going to apply a big blowing force or a wind so say I set up a big fan on the on the side and I'm blowing this nice big crosswind as the the balls are going down the bowling alley so hopefully you can kind of imagine the effect of that blowing wind on each of these scenarios is going to be a little bit different um so if we do the the ping pong ball first if I have a big blowing wind this way that pingpong ball is really light if I have a big blowing Force you can imagine it's going to deflect it might even blow the the pingpong ball off of the the alley that it's going down that same bluing Force though if I apply that to the scenario with the bowling ball might not affect it very much at all so we might get a slight deviation depending on how strong that wind is but the bowling ball is massive enough that it's it's going to basically keep moving uh along its its same path so this same sort of idea is what happens in a mass spectrometer instead of having a uh a blowing force of of wind we have uh a magnetic field which is going to set up um the the magnetic field and electric field that's going to deflect that charged particle so if I have this magnetic field um our particles are going to get deflected due to the positively charged nature of the particles going through and the amount of deflection um that they take relative to their initial path right I'm speeding them up speeding them up and if they go straight through they would land here but since I've applied that magnetic field particles that are smaller less massive are going to deflect more and they're going to hit our detector at the end at a different spot so we're able to keep track of say how many uh particles kind of go through and and deflect very little and then how many particles go through and deflect a lot and we can keep these counts and maybe we'll have some that are over here um based on the amount of particles that hit in a given sample we could say that the particles that that had this size are going to have a higher percent abundance so maybe these are like 60% of the particles hit at this spot and maybe 30% here and then maybe 10% here so based on where those particles hid that end detector at the end we're able to determine what that relative mass is and the frequency of those particles within a given sample so this is how a mass spectrometer works and how we get this percent uh abundance data once we have that data it's typically tabulated in uh a table form so here um I have three different elements that are provided so we've got our Hy nen we have carbon and we have oxygen so we have three different uh elements and we have their stable isotop so it is important that the the Isotopes that are listed here are stable isotopes there are more Isotopes for uh for these different elements um that are unstable meaning that they're radioactive so they Decay their nuclei Decay um releasing energy in particles um to different um different isotopes or different elements Al together so the the elements that are identified in the percent abundance tables are the uh stable isotopes if we look at Carbon so we have carbon 12 and carbon 13 and so what this table is telling us is that most atoms if we have a sample of carbon most of those carbon atoms in that sample are going to be carbon 12 1% 1.11% are going to be carbon 13 if we do the same with oxygen most atoms in a sample of oxygen are going to be Oxygen 16 99.7 76% of those atoms are are Oxygen 16 a trace amount so Trace is just a really really small amount Trace amount would be oxygen 17 and 2% would be oxygen 18