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Current time:0:00Total duration:17:03

Video transcript

everything we've been dealing with so far and our journey through chemistry has revolved around stability of electrons and where electrons would rather be in stable shells and like all things in life we if you explore the atom a little further you'll realize that electrons are not the only stuff that's going on in an atom that the nucleus itself has has some interactions or has some instability that needs to be relieved in some way and that's what we'll talk a little bit about in this video so and and and actually the mechanics of it or well out of the scope of a first-year chemistry course but it's good to at least know that it occurs and one day when we we study the strong nuclear force and quantum physics and all the like that we could start talking about exactly why why these protons and neutrons and the their constituent quarks are interacting the way they do but with that said let's at least think about the different types of ways that a nucleus can can essentially decay so let's say I have a bunch of protons I'll just draw a couple here some protons there and I'll draw some neutrons and I'll draw them in a in a neutral ish color maybe let me see like a grayish would be good so let me just draw some neutrons here how many pros I have 1 2 3 4 5 6 7 8 I'll do 1 2 3 4 5 6 7 8 9 neutrons and so let's say this is the nucleus of our atom and remember and this was you know in the very first video I made about the atom the nucleus if you actually were to draw the actual atom and it's actually very hard to draw an atom because it has no well-defined boundaries the electron really could be you know at any given moment it could be anywhere but if you were to just say okay where's ninety percent of the time the electron is going to be and you say that's the radius or that's the diameter of our atom we learned in that very first video that the nucleus is almost an infinitesimal portion of the volume of this of this sphere where the electron will be 90% of the time and the neat takeaway there was that well most of whatever we look at in life is just open free space all of this is just open space but I just want to repeat that because that little infinitesimal spot that we talked about before where even though it's a very small part of the fraction of the volume of an atom it's actually almost all of its mass that's what I'm zooming out to this point here these aren't atoms these aren't electrons this is as we're zoomed into the nucleus and so it turns out that sometimes the nucleus is a little bit unstable and it wants to get to a more stable configuration we're not going to go into the mechanics of exactly what defines an unstable nucleus and all that but in order to get into a more unstable nucleus sometimes it emits what's called an alpha particle or this is called alpha decay alpha alpha decay and it emits an alpha particle which sounds very fancy and it's what it's just a collection of neutrons and protons so an alpha particle is two neutrons and two protons so maybe maybe these guys they just didn't feel like they fit in just right so their collection right here and they get emitted they leave they leave the nucleus so let's just think what happens to an atom when it's when something like that happens so let's just say I have some random element I'll just call it element II let's say it has P protons actually let me do it in the color of my protons it has P protons and then it has its atomic mass number is the number of protons plus the number of neutrons and in the neutrons in gray right so when it says when it experiences alpha decay when it experiences alpha decay what happens to the element well it's protons are going to decrease by 2 so it's protons are going to be P minus 2 and then it's it's neutrons are also going to decrease by 2 so it's mass number is going to decrease by 4 so up here you'll have P minus 2 plus our neutrons minus 2 so we're going to have minus 4 so your mass is going to decrease by 4 and you're actually going to turn into a new element remember your elements were defined by the number of protons so in this alpha decay when you lose those as you're losing 2 neutrons and two protons but especially the protons are going to make you into a different element so if we call this element 1 I'm going to call we're going to be at a different element now element 2 and if you think about what's generated so we're emitting something that has two protons two protons and it has two neutrons so that's mass is going to be the mass of the two protons and two neutrons so what our readmitting we're meaning something that has a mass of four so if you look at what is two protons and two neutrons actually don't I don't have the periodic table on my I'd forgot to cut and paste it before this video but it doesn't take you long on the periodic table to find an element that has two protons and that's helium it actually has an atomic mass of four so this is actually a helium nucleus that gets emitted with alpha decay this is actually a helium nucleus a helium nucleus and because it's a helium nucleus and it has no no electrons to bounce off it's two protons you would call this this would be a helium ion so it essentially it has no it has no electrons it has two protons so it has a plus two charge plus two charge so an alpha particle is really just an a helium ion a plus two charge helium ion that is spontaneously emitted by a nucleus just to get to a more stable State now that's one type of decay let's explore the other one so let me let me draw another nucleus here I'll draw some neutrons I'll just draw some protons protons so it turns out sometimes that a a neutron doesn't feel comfortable with itself it wishes that it looks at what the protons do on a daily basis and says you know what for some reason when I look into my heart I feel like I really should be a proton if I were proton the entire nucleus would be a little bit more stable and so what it does is to become a proton remember a neutron has neutral charge so what it does is it emits an electron and I know you're saying Sal you know that's crazy I didn't even know neutrons had electrons in them and all of that and and I agree with you it is crazy and and one day we'll study all of all of what exists inside of the nucleus but let's just say that they it can emit an electron and when it emits an electron so this emits an electron so it emits an electron and we signify that with it's roughly its mass is zero we know an electron really doesn't have a zero mass but we're talking about atomic mass units if the proton is one an electron is one 1,836 of that so we just round and we say it has a mass of your mass really isn't zero its mass and its charge is minus one it's atomic you can kind of say it's atomic number is minus one so it emits an electron and by emitting an electron instead of being neutral now it turns into a proton it turns into a proton and so this is called beta decay beta decay beta decay and a beta particle is really just that emitted electron so let's go back to our little case of an element it has some number of protons and then it has some number of neutrons so you had the protons and the neutrons and you get your mass number when it experiences beta decay what happens well are the protons changed sure we have one more proton than we had before because a neutron changed into one so now our protons are plus one has our mass number changed well see this goes the neutrons goes down by one but your protons go up by one so your mass number will not change so it's still going to be P plus n so your mass stays the same unlike the situation with alpha decay but your element changes you're pro number of protons changes so now you're once again you're dealing with a new element in beta decay now let's say we had the other situation let's say we have a situation where one of these one of these protons looks at the neutrons and says you know what I I see how they live and it's very appealing to me I think I would I would fit in better and our community of particles of we could call them nuclear well we of particles within the nucleus would be happier if I two were a neutron we'd all be in a more stable condition so what they do is that little uncomfortable proton has some probability of emitting and now this is this is a new idea to you a positron not a proton it emits a positron and what's a positron it's something that has the exact same mass as an electron so it's one 1836 of the mass of a proton but we just write a zero there because in atomic mass units it's it's pretty close to zero but it has a positive charge it's a little confusing because they'll still write a there whenever I see any I see well I think an electron but no they say E because it's kind of like the same type of particle but instead of having a negative charge it has a positive charge this is a positron positron and now we're getting we're starting to get kind of exotic with our with the types of particles and stuff we're dealing with but this does happen and if you have a a proton that emits this particle that pretty much had all of its positive charge going with it this proton turns into a turns into a neutron and that is called positron emission positron emission is usually pretty easy to figure out what it is because they call it positron emission so if we start with the same E it has certain number of protons a certain number of neutrons what's the new element going to be what's going to lose a proton P minus 1 and that's going to be turned into a neutron so P is going to go down by 1 and it's going to go up by 1 so that the mass of the whole elect of the whole atom isn't going to change so it's going to be P plus n but we're still going to have a different element right when we had beta decay we increase the number of protons so we went kind of to the right in the periodic table or we increased our well you get the idea when we do positron emission we decreased our our number of protons and actually I should write that here in both of these reactions so and this is the positron emission and I'm left over with one positron and in our beta decay I'm left over with one electron they're written the exact same way you know this electron cuz it's a minus one charge you notice as a positron because it has a plus one charge now there's one last type of decayed that you should know about but it doesn't change the number of protons or neutrons and a nucleus but it just released is a ton of energy or sometimes you know a high-energy photon and that's called gamma decay and gamma decay means these guys just reconfigure themselves maybe they get a little bit closer and by doing that they release energy in the form of a very high wavelength a electromagnetic wave which is essentially a gamma you could either call it a gamma particle or a gamma gamma ray and there's very high-energy gamma rays or something you don't want to be around they're very likely to maybe kill you so let's everything we did I have set a little theoretical let's do some actual problems and figure out what type of decay we're dealing with so here I have seven beryllium where seven is its atomic mass and I haven't been converted to seven lithium so what's going on here my beryllium my my nuclear mass is staying the same but I'm going from four protons I'm going from four protons to three protons so I'm reducing my number of protons my overall mass hasn't changed so it's not it's definitely not alpha decay alpha decay was you know you're releasing a whole helium from the nucleus so what am i what am i releasing I'm kind of releasing one positive charge or I'm releasing a positron and I Drive it's here in this equation this is a positron positron so this type of decay of seven beryllium to seven lithium is positron emission fair enough now let's look at the next one we have uranium 238 decaying to thorium 234 we see that the atomic mass is decreasing by 4-4 and you see that your atomic number is decrease or your protons are decreasing by 2 so you must be releasing essentially something that has an atomic mass of 4 and an atomic number of 2 or or a helium so this is alpha decay so this right here is an alpha particle alpha particle and this this is an example of alpha decay now you're probably saying hey Sal wait something weird is happening here because if I just go from 92 protons to 90 protons I still have my 92 electrons out here so wouldn't I now have a minus 2 charge and even better I that's this helium I'm releasing this helium it doesn't have any electrons with it it's just a helium nucleus so doesn't that have a plus 2 charge and if you said that you would be absolutely correct but the reality is is that right when this decay happens this thorium it has no reason to hold on to those two electrons so those two electrons disappear and thorium becomes neutral again and this helium likewise it is very quick it really wants two electrons to get stable so it's very quick to grab two electrons out of the wherever it's bumping into and so that becomes stable so you could write it either way now let's do another one so here I have iodine release let's see what's happening my my mass is not changing so I must have just I must just have protons turning into neutrons or neutrons turning into protons and I see here that I have 53 protons and now I have 54 protons so I must have a neutron must have turned into a proton a neutron must have gone to a proton and the way that a neutron goes to a proton is by releasing an electron and we see that in this reaction right here an electron has been released and so this is beta decay this is a beta particle beta this is beta decay and that same logic holds like hey wait I just went from 53 to 54 protons don't I have you know what now that I have this extra proton won't I have a positive charge here well would but very quickly this might get maybe it'll get it's probably won't get this exact electrons there's so many electrons running around but it would grab some electrons some from someplace to get stable and then it'll be stable again but you're completely right and thinking hey wouldn't it be an ion for some small amount of time now let's do one more so we have two twenty-two radon it has an atomic number of eighty six going to two eighteen polonium with atomic number of eighty-four and this actually is an interesting aside polonium is named after Poland because Marie Curie she she at the time Poland this was at the the turn of the last century around of 1800s Poland didn't exist as a separate country it was split between Prussia Russia and Austria and they really wanted to let people know that hey you know this we think we're one people so they they discovered that when you know radon decayed it formed the settlement they named it after their motherland after Poland so just a well it's the privileges of discovering new elements but anyway back to the problem so what happened our atomic mass went down by four our atomic number went down by two once again we must have released a helium particle something a helium nucleus something that has an atomic mass of four and a and a atomic number of two and so that there we are so this is alpha decay alpha decay and this is we could write this as a helium nucleus so it has no electrons and we could even say immediately that this would have a negative charge but then it loses