all right this is mr. Lee Han teaches you stuff grade 9 chemistry lesson 9 isotopes and ions all right so why don't we start off with isotopes now an isotope is an atom with the wrong number of neutrons I put wrong in quotation marks because there isn't really a right or a wrong here it's just a helpful way to remember this and here's what I mean the atomic mass of an element is not always a whole number so if you look on the periodic table you'll notice that the atomic mass is often a decimal and this is because it's an average of many isotopes of the element so if we take a look over here at the box with chlorine in it the atomic mass says 35 decimal 4 5 and the reason why is because chlorine can potentially have either 18 19 or 20 neutrons and this would mean it would have an atomic weight of either 35 36 or 37 but you don't usually get a pure sample of just one isotope of chlorine so when you take a sample of chlorine and it's all pure chlorine atoms you're going to have a mixture of all those isotopes so if you actually weigh that sample you figure out the mass of that sample and then you divide it by the number of atoms that would be in that sample you end up figuring out that there are that each one weighs on average 35 decimal 4 or 5 atomic units or atomic mass units so that's why there are decimal places in the atomic masses on the periodic table it's because of isotopes alright next we'll move on to ions and ions are atoms with the wrong number of electrons once again there's no right or wrong here but they are atoms with an unusual number of electrons right not not the normal amount that you would expect so because they have either fewer or too many electrons they will have a charge of some sort because remember electrons are negatively charged so if you take away a negative charge they'll be positive or if you add a negative charge they'll be negative so for example oxygen atom I on of 2 - well lithium ions have a charge of 1 plus noble gases noble gases do not form ions and the reason why is because noble gases have a full valence shell so their outer shell their outer orbit there has as many electrons as it can fit so they don't form ions this is the reason why almonds form ions to have a full valence shell that's the whole reason they do it so noble gases are already done they don't need to do anything so elements will either gain or lose electrons to have a full valence shell just like the noble gases so if an element gains an electron it becomes negatively charged like chlorine so here we have chlorine to have a full valence shell it needs to gain one electron and now because it has more electrons than protons its negatively charged if an element loses an electron it becomes positively charged like potassium so here's potassium and it has that one extra electron there and its valence shell if it gets rid of that it'll be just like argon the noble gas so it gets rid of that and now it has more protons than electrons so it is positively charged so can an element lose or gain a proton instead of an electron to become an ion the answer to that is no most certainly not if the number of protons changes which it doesn't the at out the atom would be a new element so for example we have fluorine here fluorine has an atomic number top-left corner of 9 if we added a proton to that it becomes neon it's a totally different element remember that elements are defined by the number of protons in their nucleus so you can't really change that it doesn't make them anion if you change the number of protons and really you don't change the number of protons in an atom now how do you know what charge and ion would be let's figure this out so what charge does lithium form so lithium here has three electrons and it's got one in its valence shell the closest noble gas to lithium is helium so what do we need to do to make lithium look like helium well we need to get rid of this one valence electron in its valence shell if we do that then it's just like the noble gas helium it has a full valence shell because it's lost an electron it becomes positively charged so lithium forms an ion with a charge of 1 plus now what charge does a fluorine ion 1/2 so fluorine has 1 2 3 4 5 6 7 electrons in its valence shell so is it going to lose all 7 of those to be like helium or is it going to gain one to be like neon well it's going to be a heck of a lot easier to gain one then it is going to be to lose 7 so fluorine gains one electron and because it's got more electrons than protons now it has a negative charge so fluorine forms an ion of 1 - now what charged is a nitrogen ion half well nitrogen is got one two three four five and its valence shell so the closest noble gas to nitrogen is neon so it's going to be easier to gain three electrons that will be to lose five so nitrogen gains three electrons and then gets a charge of three - so nitrogen forms an ion of three - now you may remember from the last video that all the elements in a group will have the same number of valence electrons and because of this they're all going to form ions with the same charge so here's the ion charges in the periodic table the first column first group gets charges of one plus second column two plus and we get three plus and then right here it's we don't really give them charges in this column we've got carbon it has four electrons in its valence shell so if it needs eight to be stable it's either going to have to lose four or gain four so it's kind of in the middle so it doesn't really form an ion easily so we just don't give those charges now we're into the nonmetals and these form negative charges so now we have three minus two minus and one minus and then last but not least we have our noble gases which do not form ions so here we have the periodic table and this one has all the ion charges on it so in the top left sorry top right corner we have the eye on charges for all these elements and if you look closely you'll see that some elements show multiple charges so all these highlighted yellow ones they have more than one ion charge now these are called multivalent elements and some metals can form more than one stable ion so if we look at the box for copper for example you'll see in the top right you have the ion charges that it can form it can form either 2 + or 1 + so copper can have a charge of 1 + or 2 + which means it can either lose one electron or two electrons and become stable if we look at iron iron can form an ion of 3 + or 2 + which means iron can become stable by either losing 3 electrons or losing two electrons so those are multivalent elements now it's important to notice that the first 20 elements all have only one stable ion so chances are if on a test you get an element that isn't one of the first 20 your teachers put it there because it is a multivalent element so that's that's a good thing to watch out for on tests polyatomic ions another type of ion now sometimes a group of atoms can act like a single ion so for example carbonate carbonate is Co 3 2 - now what that means is that the whole Co 3 that carbon and those 3 oxygen all mixed together they all have a charge of 2 - so that whole thing has 1 charge of 2 - the whole group so that means that carbonate acts similar to an oxygen ion or a sulfur ion which are also 2 - and because this polyatomic ion is negatively charged it will react with positively charged metal ions and we'll get into that in the next video but the important part to remember here is that the whole group of atoms behaves similar to just one single ion so another group is a hydroxide group which has a charge of negative 1 or 1 1 - I guess a sulfate group and a phosphate group and if you look at the names here except for the hydroxide you'll notice that everything ends with 8 that's a good thing to note if you're ever looking at something and it says carbonate or sulfate or phosphate instead of phosphide then you'll know that you're probably dealing with a polyatomic ion alright so that's it for this video tune in to the next video ionic compounds part 1