hello welcome to the penguin Prof channel today I want to get started on a chemistry concept series by popular demand we're going to be talking about elements atoms really why it's all about the electrons and some Lewis dot structures which in my opinion may be the key to happiness when we get started here we're really talking about what stuff is made of and stuff is made of matter from here you can really kind of go off a cliff in terms of how far you want to go into this this is really the realm of physics so I just want to say from the outset that this is a highly abbreviated version of an understanding of what the stuff is in the universe the matter is made of elements elements are pure chemical substances that you can't break down into anything else now we organize elements in this amazing table called the periodic table of the elements it's really amazingly organized and I mean I'm just gonna say it it's beautiful ok how much of a geek am I to say that but it really is because if you understand how this table is organized this is tremendously powerful notice I didn't say if you memorize it I do not have my students memorize any part of this table that's what it's there for that's why you can look it up but you have to understand how to use it and what it means in terms of elements in the universe the vast majority of them are the two smallest elements hydrogen and helium on our planet in the Earth's crust by weight we've got oxygen silicon and aluminum if you take the earth as a whole not just the crust by weight the most abundant element is iron in terms of biology only 25 elements are essential for life and of those 25 only for makeup the vast majority of most living things including penguins so if you're wondering well what are we made of you'll be thrilled to know that you can actually buy a shirt with human ingredients on it oh my gosh I love these geeky gifts I don't know what that barcode is at the bottom but anyway so here's a nicer view table of the elements of the human body and again you can see that 9 over 96% of humans are made of oxygen carbon hydrogen and nitrogen so if you go back to the periodic table and it is kind of overwhelming I admit but you remove all of the elements that are not found in humans it's really not too bad at all this this looks somewhat manageable right understanding the periodic table also allows you to understand all these stupid geeky gifts like this bacon shirt which I just I don't know I was just in a weird mood okay so the smallest unit of an element which retains all of the properties of that element is called an atom that word comes from the Greek a term which means not to be divisible meaning you can't cut it up into smaller pieces and still retain the properties of the element we can actually see atoms today this is a really cool transmission electron micrograph done by the physicists at UC Berkeley the red arrows are hydrogen that black arrow is a carbon atom shown on the surface of graphene now in your textbook you will see atoms drawn like this electron clouds the shell or Bohr model and I gotta be honest with you this is just not true atoms do not look like this we use these drawings because they represent it sort of an easier way for us to talk about them but this is not what atoms really look like atoms are really hard for us to wrap our brains around because they are unbelievably small that black bar right here at the bottom represents one angstrom or 100,000 of femtometers so an angstrom is 10 to the minus 10 meter and the vast majority of the atom is actually empty space so over 99% of the mass of the atom is concentrated at the center in the nucleus and the rest of it where the electrons are the orbitals are just hugely spread out and it is really difficult for us to really draw and think about what atoms really look like so I have a couple of analogies for you of course one is an analogy of scale and this is a soccer field and if you take the nucleus to be the size of the soccer ball then an electron could be a fly buzzing around the spectators and most of the stadium represents the space between the atomic nucleus and the electron so most of the atom is empty space now this analogy is not really accurate either because it shows the electron as a particle as a fly and actually that's not true one of the best analogies that a chemist gave me for this is with cotton candy and he said okay where's the sugar well the sugar is kind of everywhere I mean the whole cotton candy is made of sugar that's kind of the same idea with these electrons so the orbital itself really is the electron but that's really hard to draw and describe so what I always say is you know strive for understanding strive for the real truth but we like all of your textbooks and basically everybody else we're going to use these models and drawings we're gonna draw the little electron as like a ball or a bead so that we can keep track of everything okay but realize that that's not really the truth so getting back to the atoms in the periodic table there's a couple of numbers that we need to concern ourselves with one is the atomic number and that's just the number of protons that an element has and I'm picking carbon here as an example the atomic number for carbon is 6 what that means is that carbon has 6 protons that number does not change it's kind of like your calling card so if you add a proton to carbon it's not carbon anymore so now your atomic number would be 7 and now your nitrogen so the atomic number does not change the mass number or what we call the atomic weight that's the number of protons plus the number of neutrons the first thing that you notice is that these numbers are decimals so maybe you're wondering well are there fractional protons and fractional neutrons and you know what's up with that well what we're really getting at here is the mass number is actually an average so the number of protons does not change but the number of neutrons can change so if we look at carbon carbon in the universe there are different numbers of neutrons in various carbon atoms that you could find we call these isotopes most carbons in the universe have six neutrons and of course the number of protons doesn't change so 6 plus 6 is 12 so the vast majority of carbons that you would find have the mass number of 12 you will also find those some carbon atoms with an extra Neutron and if you add 6 plus 7 that gives you the mass number of 13 some atoms have two extra neutrons 2 more than the normal number and the mass number here is 14 this is probably the one that you're most familiar with carbon-14 is what we use for dating not not dating will you go out with me but dating how old is that tree we use isotopes for all kinds of purposes actually in medicine as well as radioactive dating because they decay at a constant rate so if you look at the decay rate of carbon-14 this is what it means so we have x 0 some amount of carbon-14 that's present after one half-life which for carbon-14 is about five thousand years after one half-life you have half that amount still remaining after two half-lives you have half of that half and after three half-lives you got another half so it's not like after two half-lives it's all gone that's a big misconception so what you should notice is this exponential rate of decay and this rate is constant so that's why we can use isotopes to date living tissue to date rocks and things like that but enough about the nucleus chemistry is really all about electrons so we're going to spend the rest of this video talking about them now atoms like to be stable and in order to become stable sometimes they have to play with other atoms in this way they're kind of like people but you might ask the question does everybody need to play with others in order to be happy humans are social creatures so most of us do but there are actually individuals that don't and the same thing is true in the periodic table we have to the far right the noble gases noble gases so named because like nobility they do not mix with the commoners and in this video we're going to explore why why don't they form bonds with other atoms everybody else on the table they form bonds but not the noble gases you've got to understand the electrons in order to understand why so electrons fill around the nucleus from the inside out and what I mean by that is as you look at different atoms and different atoms have different numbers of electrons they will fill around those nuclei from the inside out just like water fills in a glass when you fill a glass with water it fills from the bottom up ok you can't do it any other way if you can I'd like to see that shell number one is gonna hold two electrons shells 2 & 3 are gonna hold 8 yes for you chemists I am oversimplifying this when you go on and take more general chemistry you will see that e electron configurations are a little more complicated than that but for the purposes of general biology what I'm giving you should get you through most of the problems that you're going to come in contact with I've just got to say don't don't get your heart rates up when you see stuff like this even at first glance you notice that there is a pattern so there really this is manageable but we're not going to go into that in this video we're gonna focus on happiness what you got to remember is that atoms are happy when their outer shell is full of electrons the outer shell turns out to be so important we actually give it a name we call it the valence shell so we're going to talk about how they get to be happy right now as we go through this we're going to see that carbon is not happy by itself whereas neon is we're gonna see why my analogy for this is a stadium in the round so a stadium with a stage inside and spectators all the way around and of course we're gonna have penguins in there too so we're gonna have a rule and a goal the rule is we're gonna sell tickets closest to the stage first the goal is we want to make each shell around the stage full of spectators now in our little theater it's to be a very little theater the first shell is only going to have two seats in it the second shell is going to have eight seats and the third shell is also going to have eight seats so just go with me on this okay it's a small intimate theater so here are our seats if we're gonna look at different scenarios and see what it looks like so here's the first scenario we sell one ticket so we're gonna satisfy the rule the the tickets that we sell are going to be closest to the stage the goal is not met though so that's not so happy we have one empty seat in the first ring and this is actually hydrogen another scenario we sell two tickets so the rule is they're going to be the ones closest to the stage so that's all good and we actually met the goal the shell is full so that's a really happy stable scenario and this is actually the element helium what if we sell seven tickets so notice the rule we're selling the tickets closest to the stage first but you notice now that we have three empty seats in that second shell so this is nitrogen this explains why nitrogen would want to form bonds to try and fill those empty seats what if we sell ten tickets though now you notice that the first two shells are full this is a very stable configuration and this is actually the noble gas neon what about 13 tickets so now we're moving into that third shell we're always filling from the inside out but now that third shell has only three occupied seats and five empty ones so that's not so happy and that is the element aluminum in our last example we have 18 seats and you notice we have all three shells full this is a very stable configuration this is the noble gas argon so maybe you've noticed that it seems to be about the valence shell if the valence shell is so important why don't we just focus on that I mean who cares what the core of the beast looks like let's just look at the outer shell since that's what's going to determine how happy an atom is if you're thinking that that's awesome you're not alone because some other really smart people have thought exactly the same thing like dr. Gilbert Lewis who is a physical chemist he spent most of his career at UC Berkeley and he did exactly that he said we should draw elemental symbol and then we're gonna draw the valence shell electrons around it and I always tell my students if you keep track of the valence electrons you're gonna be happy so let's see how this works we're gonna look at carbon the most important part in terms of carbons reactivity is the valence shell so let's just get rid of everything else and we're gonna draw only the electrons in the valence shell around carbon that's the most important part so carbon has the atomic number six and now you know that two of those electrons are in the first shell leaving four for the valence shell now I just want to remind you those penguins represented electrons but for heaven's sakes don't draw penguins and your Lewis and dot structures you're gonna get kicked out of class so what we do is we draw literally dots around the element to represent the valence electrons and that is the lewis dot structure for carbon how easy is that so let's look at nitrogen so to draw the Lewis dot structure for nitrogen all you do is you draw the symbol for nitrogen and then you go around it and draw the valence electrons starting at the top now this how you draw these varies this is the way that I was taught starting at the top and going around nitrogen looks like that so let's look at aluminum so here's the symbol for aluminum aluminum has three electrons in its valence shell so you draw them around going one two three that's aluminum so finally let's do argon argon has a full valence shell so we're gonna draw one two three four five six seven eight a full valence shell for argon and it's as simple as that so check this out if you look down the column of all the noble gases and you draw the Lewis dot structures for each one you will find that they all look the same because all of them have full valence shells and this explains why all the noble gases are happy as they are and they don't form bonds with other atoms because if the goal is to have a full valence shell and you already have one you don't need to play with others the only thing that might confuse you is helium and what you have to remember is that helium is very small atomic number two so it has only two electrons and so you have to remember that that first shell is in fact full with two where as everybody else going down this group they will all have an outer shell full with eight so let's practice when you practice drawing the Lewis structures all you need without the Penguins is a periodic table so lithium atomic number three it's gonna have two electrons in the first shell leaving you one in the second shell so when you draw the Lewis dot structure that's it one electron in the valence shell for oxygen you've got two electrons in the first shell six in the second for a total of eight so you draw your oxygen with one two three four five six electrons in the valence shell that's your Lewis dot structure for oxygen sodium has two in the first shell eight in the second one in the third for a total of eleven sodium is drawn just like that so it's really not too bad and even though most biology instructors don't really show you Lewis dot structures you're gonna have to do it in chemistry anyway and truthfully if you understand Lewis dot structures everything else is going to make a lot more sense so here are the first twenty elements and the Lewis dot structures for each and what you notice is that as you go down the vertical columns which we call groups they all have the same Lewis dot structures and that explains why they have the same chemical reactivity and why they'll form the same kind of bond isn't that cool how powerful is that so understanding Lewis dot structures is gonna make predicting atomic interactions so much easier and you're gonna be able to predict what's gonna happen when for example two hydrogen atoms get together because unless you're a noble gas you're gonna have to play with others in order to become happy and that's what atomic bonding is and that's why two hydrogen's get together to form h2 hydrogen gas so they're both going to share their lone electron so that each one can have a stable full shell as always I hope this was helpful thank you so much for visiting the penguin Prof Channel please support by clicking like comment share and subscribe and join us on Facebook follow on Twitter as always good luck