all right so I want to talk about one of my favorite topics which is isotopes Isotopes aside from being the name of a baseball team is a term for when you're talking about a collection of atoms all of the same element but with a specific number of neutrons this will make more sense as you see the math of what's going on all right so just a review when we're looking at an element tile on the periodic table we have these pieces of information you have the atomic number at the top which tells you the number of protons you have for that element we're going to be working mostly with the example of carbon today carbon by definition is an atom with six protons in it here at the bottom we have the atomic mass I like to think of it as a weighted average of atomic masses for the different isotopes carbon has mostly carbon 12 okay as I write here carbon 12 is 99% of the carbon on Earth and that 12 comes from having six protons and six neutrons in its nucleus 6+ 6 you get that number 12 all right 1% of the carbon on Earth approximately is carbon 13 that comes from having six protons and seven neutrons 6 + 7 you get 13 now that word weighted and weighted average can confuse people waiting in a mathematical sense just means that since the 99% of the carbon 12 is the dominant form of carbon the average is going to skew closer to the 12 we see that here 12.0 011 that's the weighted average that's the um atomic mass of carbon we can see that on average it's going to be closer to 12 because we have more of the carbon 12 you can't simply just add 12 and 13 get 25 divide by two and get 12 and a half because that wouldn't accurately reflect that most of the carbon is carbon 12 hopefully that makes sense okay so yeah those are the two main isotopes of carbon on Earth there's also a little bit of carbon 14 coming from cosmic radiation um that's the radioactive form of carbon we have on Earth uh thankfully that's only about like one in a million carbon atoms or so and that's useful for when people are doing radiometric dating such as carbon dating to figure out the um time since uh an organic organism a carbon containing a thing uh passed away all right so there there's applications for all this all right anywh who so let's get on with it uh this is going to be our isotope symbol template X just meaning whatever your element symbol is I got some examples here if you want to look at those um so for carbon we would just put a c here and then some new terminology so Z is the number of protons also known as the atomic number we may have uh heard of that one before but a is often a new one for many that's called the mass number mass number is not the actual mass you're not like weighing it or anything like that I mean it'll be close to that weight or mass but it's actually just a pure counting number It's actually an exact number uh just like Z is an exact number to get the Atomic or excuse me the mass number you're going to add the number of protons the atomic number and you're going to add n which is the number of neutrons there okay so you add up your number of protons your number of neutrons and you get this thing called the mass number now n the number of neutrons usually is not put on the isotope symbol and that's because people who work in the nuclear Fields uh radiochemist nuclear chemist nuclear physicists physicists chemists we often actually don't really need that number neutrons we're often more interested in just the overall contribution to mass the mass number than the specific number of neutrons that being said sometimes we do need that number so it's important that you know how to calculate it so let me slide this over so we got some examples with carbon I'll just shrink this hopefully the lip reading is still okay there there we go so we talked about those three different isotopes of carbon earlier carbon 12 carbon 13 carbon 14 using this template here's how we would write out those symbols at the bottom left we write the number of protons the atomic number Z and at the top left we write the mass number you can see that when we're talking about a specific isotope we say the name and then we say the mass number we don't mention in the name of the isotope we don't mention the Z the number of protons and that because that's because you can already tell what that is just from the name alone so for carbon 12 put a six there you put a 12 there if you're interested in calculating the number of neutrons you would use this formula here you would rearrange it so that's N = A minus Z 12 - 6 and we get that six all right so for carbon 12 the dominant form of carbon on Earth it has the same same number of protons as neutrons all right so for the remainder of this video let's do some examples together first we're going to create some isotope symbols together and then we're going to look at some symbols and give the a z and N values uh for those all right so we have first uranium 235 this will require us to have a periodic table handy ptable.com is a I like to go to this place easy to read so let's look for uh uranium uranium is element number 92 there is that weighted average at the bottom 23803 but that's taking all uranium Isotopes into consideration so we don't have to actually worry about that number too much when we're working with Isotopes specific Isotopes all right so I'm going to write let's take a different color pen so you can see my answers of course pause this video um to work on these on your own first and then we'll compare all right we got um a z of 92 same for the next problem so we'd go 235 92 and then we'll put a u for uranium 238 similar answer how about cesium 137 let's look up cesium CS and I guess cesium can also be spelled like that all right so cesium was element 55 we have 137 CS all right stonum 90 there's strum number 38 all right and you may have seen earlier like here I showed the isotope symbols without the atomic number Z that is an option for writing out an atomic uh an isotope symbol because just from the symbol you'll already know what the element is and therefore you know how many protons it has for starting out I recommend you do it this way and then um with some practice that should be something you should be able to do as well all right let's keep going so we got Florine 18 all right Florine is element number nine and then we have technum 99 technum is the first artificial element appearing on a periodic table 43 is the earliest instance you have that and there is technum 99 all right let's move to these examples all right in the previous examples we weren't concerned with the neutron number but we'll work that into our analysis this time so to change it up I gave isotope symbols so we those are already made for us we're just going to now extract the information from those isotope symbols all right and we can color code and shape code this I'll like that red boxes for those just to remind ourselves that we don't have to calculate that it's already provided I'll do the same thing with the Z's I'll use a green circle and then for the NS well uh that doesn't go into isotope symbol so we will have to calculate that okay so spend a minute or two working on these and then you can compare with my answers all right here are my answers all right so here here we have prodium this is the most dominant form of hydrogen uh not just on Earth but in the universe all right prodium uh just having a mass number of one okay so this is hydrogen one that's most hydrogen here we have hydrogen 2 also known as dyum and here we have hydrogen 3 also known as tridium right but again most hydrogen this form these two if you're curious about it are stable whereas this tridium is radioactive all right let's calculate a z and when I have multiple on the same page I just like to set all this up all right so hydrogen one has a mass number of one it has one proton 1 - 1 = 0 and maybe I should have uh whoops Rewritten the formula somewhere just to remind you we get it from a minus Z so this is interesting hydrogen 1 has no neutrons no neutrons all right this is rare uh this is the only instance of a stable element a stable isotope having no neutrons whatsoever okay so in fact if I had a neutral atom of hydrogen one but then I knocked off one of its electrons it would only have a proton left so the nickname for a hydrogen ion is a proton all right let's keep this going hydrogen 2 mass number of two still just one proton because it's hydrogen so we're going to do 2 -1 one Neutron right so dyum has a mass number of two as a result of having one proton and one Neutron all right we got hydrogen 3 with two neutrons now let's do some oxygen stuff so that's Oxygen 16 here we have oxygen 17 all right and then lastly oxygen 18 all right there we go all right got one last final thought in case the definition of isotope wasn't fully clear okay so once again if I'm referring to a specific isotope I'm referring to just something with some set number of protons and some set number of neutrons that's if we're saying isotope singular if we're saying Isotopes plural you may be referring to a set of atoms of the same element but with different numbers of neutrons in other words right here we have a set of Isotopes these are two different Boron Isotopes in order to be called Isotopes you have to be the same element uh but they have different number of neutrons so they're they're Isotopes because um you can have the same you have to have the same Z but you can be different in your number of neutrons and therefore your uh mass number all right to be an isobar this is not a term we use too much in chem 101 so I wouldn't worry a ton about it I'm just putting it out there so you can help form a better definition of isotope but if you're interested an isobar is when you have two things with the same mass number but you have a different Elemental identity in other words you have a different Z so right here we have potassium 40 and calcium 40 they have the same mass number but they're not the same element so those would be isobars but again at the chem1 one level we're usually talking about Isotopes more than isobars all right hope this helps have a great day and any questions uh leave them in the comments or comments leave comments in the comments uh whatever all right thanks bye