atomic theory and atomic structure that is going to be the topic of interest here in this lesson uh this is the third chapter in my high school chemistry playlist uh on atoms molecules and ions we'll follow up this lesson with an introduction to the periodic table and then finish this chapter off with nomenclature which is just a fancy way of saying naming compounds now this is my brand new high school chemistry playlist i'll be releasing these lessons weekly throughout the 2020-21 school year so if you don't want to miss one subscribe to the channel click the bell notifications you'll be notified every time i put one of these up so atomic theory is the first thing i'm going to tackle here and atomic theory uh went through several iterations to kind of get where it was so sometimes you'll hear people talk about modern atomic theory uh because some of the earlier things had slightly different uh views and stuff like that it kind of went through a process to get where it is and john dalton's responsible for pioneering this he's one of the the big people in history you're going to want to know for this chapter so but they're really four tenets to modern atomic theory and you kind of got to know them all and the first part is just that all of matter is composed of these little atoms that's the first part so cool second part deals with elements on the periodic table and then all of the atoms of an element are the same and then all of the atoms of all the other elements then are different than the one you're looking at so so if you look at all the different elements on the periodic table that's the number of different types of atoms that exist so carbon atoms are the same as other carbon atoms but carbon atoms are different than oxygen atoms essentially now third tenet of atomic theory says that you can't convert the atoms of one element into atoms of a different type of element at least not my normal chemical reactions so it turns out there are nuclear decay processes like nuclear radiation so where some of this actually does actually happen but my normal chemical means it's not possible there used to be alchemists back uh several hundred years who used to try and convert lead into gold and things of his sort uh and by normal chemical means it was never going to happen all right finally the fourth tenet of atomic theory is that the the atoms of the different elements are going to combine in different whole number ratios to form compounds that's where compounds come from so if we look at like the formula for water water is h2o so and what this means is that so to form water you're going to take two hydrogen atoms for every one oxygen atom so whether you have a small sample of water or a big sample of water if you actually split apart all the atoms and counted them up you would have twice as many hydrogen atoms as oxygen atoms they mix in a two to one ratio cool so that's atomic theory and as i said before this again was pioneered by john dalton and i don't care if you really know their first names but probably they're four guys really and possibly a fifth but we'll go with four uh names you should probably know for the history kind of pioneering atomic structure here so when john dalton's the first and you should just know that yep he's kind of like the father of modern atomic theory he pioneered atomic theory came up with his version of atomic theory good to know for him so next guy on the list is thompson that's j.j thompson and jj thompson discovered the electron and uh it turns out he discovered what's called a cathode tube which is just a beam of electrons and they made these cathode rays but long before they ever knew they were actually a beam of electrons so but he found out they were a beam of charged particles so and things of this sort but he found out the the mass to charge ratio of electrons but he didn't know the mass or the charge individually just that ratio so but he's credited largely with discovering the electrons that's what you'd kind of take away with with jj thompson's name uh robert milliken is the next on the list and milliken took thompson's work a step further and he actually figured out the charge on an electron and he's got his famous we called it the oil drop experiment all he did was take some some small little micro droplets droplets of oil and he charged them with electrons and what he found is that every single one of these droplets had a multiple of a certain charge and he figured well that smallest charge these are all multiples of that that are on these little droplets that must be the fundamental charge and turns out that's the charge of an electron so it is the smallest you know unit of charge that's possible and when something's you know either positively or negatively charged it is always a multiple of the charge on an electron so and because thompson had already figured out the mass to charge ratio once he figured out the actual charge on electron he was then able to use thompson's ratio and figure out the mass of an electron as well so but take that with you that milliken figured out therefore both the charge and then by default or or indirectly the mass of an electron uh and then finally rutherford's the next guy and rutherford took a thin thin super thin piece of gold foil and he shined alpha particles which is a form of nuclear radiation at this gold foil so and when he shined the alpha particles at this gold foil interesting thing enough is most of them just passed right through so and this was you know kind of a unique discovery but every once in a while some of them would get scattered in different directions or even bounce back in some cases and so what he presumed then is that this gold foil was made up of mostly empty space so with then concentrated areas of both mass and charge and we now know that those concentrated areas of mass and charge are the nucleus of an atom and so but big thing you should know is that ernest rutherford discovered the nucleus with his shining alpha particles through thin gold foil so that's kind of the basis these four guys you should know their last name and associate them just a little bit with what they did so i kind of tried to give you the bare minimum on the study guide there cool now i gave you also a little model of the atom there so because we want to talk about the structure of an atom so now that we know that all of matter is made of atoms now we want to talk about what's the atom made of well there's really three what we call subatomic particles and subatomic meaning smaller than the atom so and that's the proton the neutron and the electron so let's take a look at these for a second so we've got the proton which we symbolize with the letter p the neutron with the letter n and then the electron with the letter e and oftentimes we'll put a little e negative on it so it turns out that two of these particles are charged so it turns out that protons are positively charged electrons are negatively charged and they're attracted to each other so and then neutrons are neutral they have no charge which is you know the source of all sorts of stupid jokes out there right you know neutron walks into the bar orders a drink says how much will it be and the bartender says for you no charge yeah it's terrible so i told you in the first lesson that this wouldn't be that it wouldn't be the last lame joke you heard and now i'm making good on that all right so if we take a look at the protons neutrons and electrons and what's really going on inside of an atom so at the center of an atom so this is where you get protons and neutrons this is your nucleus and then going around this nucleus are going to be some electrons so and we call it an electron cloud and they're just kind of moving around and stuff like this and so the protons are positive so and then therefore these electrons they stay associated with atoms just based on the attraction to the protons in the nucleus so they're attracted to the nucleus just that plus minus attraction cool now it turns out that protons and neutrons roughly weigh about the same amount and if we tried to weigh that in like grams or kilograms it would be a ridiculously tiny number because these are really really small so what they did is invented a whole new unit they called it the atomic mass unit or amu for an abbreviation uh just specifically for talking about this stuff it's kind of like saying hey chad how many miles tall are you well that's not really a convenient unit to get my height so but if you said hey chad how many inches tall are you we could go there we could go like 68. so things of his source so uh it's just picking a more convenient units talk about the mass of these guys because if we talked about the the mass and grams it'd be like you know 1.67 times 10 to the negative 24 grams or 10 to the negative 27 kilograms or it'd be stupid you know small numbers so what they said we'll just make this easy roughly one amu for the proton roughly one amu for the neutron so but it turns out if you're really one eighteen hundred and twenty second of an amu for an electron so a super small fraction here so electrons are far tinier than the protons and neutrons and so as a result then almost all of the mass of an atom is concentrated in that nucleus right at the center with these little teeny tiny electrons floating around now to just kind of give you some scope here some scale here so think about this this is one eighteen hundred and twenty seconds wait for the electron of the proton or neutron this is kind of like comparing a small car to a baseball these electrons are way tinier than the protons and neutrons and here's where things are going to get a little crazy and mind-boggling if you kind of look at you know how big the nucleus is compared to how big the whole atom is that's where you're going to see that the scale drawing in your study guide there is way off so if you say let's say we had the nucleus here which again is super tiny but let's just say we had it and we built a scale model and we used a marble for the nucleus just a regular standard marble so what you'd find is that the electron cloud around that nucleus would probably be about half a mile in diameter so a little marble nucleus where almost all the mass is concentrated in the atom and then half a mile for the electron cloud with these super teeny tiny electrons going around so pretty crazy and so this kind of goes hand in hand with what rutherford discovered is that you know most of an atom is made of empty space and you know every once in a blue moon you get some concentrated mass and charge when you hit that nucleus but most of an atom is made of empty space now this is kind of mind-boggling because you know things feel solid you know but they're not they're made of mostly empty space so think about this for a second if you leave the earth's atmosphere and go out into space now they call it space because it's mostly empty space now the truth is even in empty space it's not completely empty every once in a blue moon you're going to like bump into a hydrogen atom but not very often so it's almost completely empty space but then even when you come you know the surface of the earth and you start touching matter and stuff like that even that matter is made of mostly empty space most of the universe whether you're out in space or on a planet is made of most mostly empty space it is mind-boggling so if i asked you what is most of this you know what is most of the stuff in between my ears made up of you should say empty space that's right cool so most of the universe made of empty space which you just learned all right so uh cool so now we know what a nucleus is made up of we want to move on to talking about isotope symbols and we're going to specifically look at oxygen here so in oxygen 16 8 we'll put a minus 2 up there we'll get rid of these guys all right so all those protons neutrons electrons we need to account for them and this is called an isotope symbol right here and specifically the o here stands for oxygen so we've got a whole bunch of symbols on the periodic table and we're going to do a little more formal introduction of the periodic table in a minute but o stands for oxygen so most of the time teachers are not going to make you memorize all of the elements of the periodic table but it does on occasion happen so however i will let you know in college it almost never happens so because we know that you're going to have the internet and you're going to have a periodic table on you at all times you know you'll have a periodic table on your sock in some cases i've seen skirts i've seen shoes i've seen ties i've seen tattoos it's crazy there's pair of tables everywhere it's on the front cover of your book you know so it's on the wall in every chemistry room at most universities so you're always going to have access to a periodic table and so memorizing you know the entire periodic table is pretty much a waste of time but it is a requirement on students every once in a while and if that's the case for you and your class i apologize so but what i do recommend is this probably just memorize the first 30. and when i say memorize the first 30 i don't even memorize like their atomic numbers or anything like that i just want you to know that zn stands for zinc know what the symbol what element it actually stands for so o is for auction f is for fluorine b is for boron that kind of thing up to the first 30. just you can work with them and most of the time it's not so bad right c is for carbon usually the letter corresponds to the element right so there's a couple exceptions right you know you go to fe right here and fe is iron so and it turns out they use the latin root fair so for that instead and for some of these they end up using a latin root i apologize so this would be a little more challenging but most of the time knowing that zn is inc not so bad knowing that ni is nickel again kind of makes sense but cool associate the names of the symbols for at least the first 30. any of the rest you need to know you'll kind of get familiarized as you go through the process so but highly recommend there all right so if we take a look at this isotope symbol so we call this bottom number here the atomic number and it always gives you the number of protons every single time so when i see this i know that we've got eight protons now the truth is this though they don't actually have to give you the atomic number they can erase it and there you go so the idea is that if you look the entire periodic table is organized by atomic number and oxygen by definition that's the number in blue here is atomic number eight so the number of protons determines what elements you have so however many new you know protons are in the nucleus that is going to identify the element for you so if it's eight protons the nucleus that's oxygen period done and so in this case because oxygen is atomic number eight is associated with having eight protons it doesn't actually have to be given here so but i put it on there just so we could actually talk about it so but that's the one number they can leave off of an isotope symbol now the top one here we call the mass number so and that mass number is kind of like a rounded whole number and if you recall i erased it protons weighed about 1 amu neutrons weighed about 1 amu and electrons weigh a super duper duper duper tiny tiny tiny fraction of an amu and so what you really get here with this mass number since uh protons and neutrons each weigh one amu this really and the electrons weigh almost zero not exactly zero but almost zero so this number really just gets you the total number of protons plus neutrons and so in this case oxygen 16 here so that mass number corresponds to having 16 total protons and neutrons combined well if the atomic number already gave us the fact that we have eight protons then the remainder must all be neutrons up to 16 total and so that's going to tell us that we must have eight neutrons as well cool so finally off on the other side here we've got the charge so and it turns out that atoms can often lose and or gain electrons from the electron cloud so they typically aren't going to lose or gain protons or neutrons from the nucleus at least not by normal chemical means but they can lose or gain electrons from the electron cloud and so when you see that you've got a negative charge here that means you've got two more negative charges than positive charges so in this case with oxygen having eight protons which are positively charged to have a negative two charge there must be two additional electrons associated with this atom and so in this case we can figure out that we've got 10 electrons with this oxygen ion now one thing to note when we have a an atom with no overall charge it must be because the protons and electrons are exactly the same number so if this didn't actually have a charge listed there if it just blank that would imply that for the eight protons in oxygen you also would have eight electrons not like the one we've got here and when you've got a neutral species that's when we call it a neutral atom but the moment you get a charge species rather than calling it a charged atom which is kind of technically true but not the not the the system of uh uh naming things we use not the definitions we use in this case we call this an ion so neutral atoms are neutral atoms or atoms but charge species we call ions so first little piece of vocabulary here cool uh a couple other things you should know so it turns out this is the most common version of oxygen but it's not the only one so there's another one out there that exists so called oxygen 18. in this case it's got a mass number of 18 and the reason it's got a mass number of 18 must be because let's work it out uh in this case because it's oxygen it still has an atomic number of eight even if it's not listed and must have eight protons but with a mass number of 18 now that means again this is protons and neutrons combined and there's eight protons so there must be ten neutrons cool so it turns out that different uh uh there are different versions of the same element some heavier some lighter so with a heavier mass number lighter mass number and we call these different thinking of the definition as i write this isotopes so iso means the same so but you've got different types of the same element so and it's just because there's a different number of neutrons leading to a different mass number that's what isotopes are they're different types of the same element different mass due to different number of neutrons in the nucleus okay last topic in this lesson we've got to talk about atomic weight also called atomic mass all right so if you look at a typical periodic table here so we've talked about having an atomic number above the same atomic number we saw in the isotope symbol i just erased but what you also have down below is an atomic mass or atomic weight so if like for oxygen here it's 15.9994 so you get a nice little decimal number and stuff like this and for carbon it's 12.011 things of this sort so what's weird is students don't often get this is that these numbers here these atomic masses or atomic weights are averages so we just saw that there are different isotopes of oxygen that actually exist so it turns out one of the common ones was oxygen 16 and then probably the next most common the oxygen 18 so but it turns out there's not a whole lot of oxygen 18 out there in natural abundance and that's why when you take the average it comes out almost exactly to 16 because pretty close to 100 of the naturally occurring oxygen atoms weigh 16 and so when you take the average it comes out really close to 16. same thing with carbon so 98.9 of naturally occurring carbon atoms weigh 12 and so when you take the average of all of them it comes out really close to 12. and for most elements this is how it works most of them have one major isotope and when you take an average of all the weights of all the naturally occurring isotopes it comes really close to one whole number because that's most of it but there's a couple elements where that's totally not the case and one of them here is chlorine so if you look on your hand out there i gave you a table there are two major isotopes for chlorine not just one and there's chlorine 35 and chlorine 37. so and i put their exact masses to two decimal places anyways so 34.97 amu's versus 36 0.97 amuse and then i also gave their natural abundances so here it's it's roughly a three to one ratio so roughly 75 to 25 percent but if we give it exactly let's go 75.8 percent versus 24 point two percent now it turns out there's trace amounts of chlorine 36 that exist but when i say trace amounts i mean like point zero zero zero zero zero zero zero zero zero zero something percent it's super tiny that we can pretty much for all practical purposes ignore it but for chlorine 35 and 37 we've got a fair amount of both now i can see that we have significantly more chlorine 35 though and so with 75 and close to 76 percent and when we take the average here then the average should have come out closer to 35 than it should to 37. and that's what we see on the predict table it's 35.4527 so a lot of periodic tables you'll see round to the two decimal places and just say 35.45 cool our students look at something like that they're like so i know it's got 17 protons because atomic number 17. so does it have like 18 and a half neutrons or something well you can't have half a neutron it doesn't work that way and the key is that this number isn't the same thing as a mass number that we saw on the isotope symbols that isotope symbol that mass number was a specific mass for a specific isotope whereas this number right here is the average mass for all the naturally occurring isotopes cool and you've got another process for how we calculate these based on giving just this kind of information so and we're going to do what's called a weighted average and you're going to take the percentage here and turn that into its decimal form and notice 75.8 percent means 75.8 over 100 which means move the decimal black back two places here so we'll have 0.758 and you'll multiply that by the corresponding mass of that isotope so multiply that by 34.9 so cool we'll do the same thing with the other isotope so we've got 24.2 percent means per 100 so 24.2 over 100 which again just means move the decimal back two places so that's 0.242 times its corresponding mass 36.97 cool and then you'll just add them together and that will get you this weighted average and let me pull out my trusty calculator here all right so .758 times 34.97 plus point two four two times thirty six point nine seven and we get thirty five point four five four and if we look 35.454 is pretty close so now i rounded these to two decimal places and i rounded these to one decimal place on the percents and had i not rounded them we would have got even closer to this number you see published on the periodic table cool but big takeaway here again so one the process for just calculating these atomic masses and again when we say atomic weight or atomic mass that already implies an average of the naturally occurring isotopes cool and that's what's published on the periodic table here cool that sums up this lesson on atomic theory and atomic structure in a chapter on atoms molecules and ions so if you feel like you got something out of this lesson please consider giving me a like and a share one of the best things you can do to support this channel and if you're looking for practice materials or the study guides that go with these check out my premium course on chatsprep.com