this is Leon so from science scribe and in this tutorial I'm going to show you how to write ionic formula but before we do that let's recap some of the skills you should be comfortable with the first is that you should be okay with drawing atoms so if I got you to draw the sodium and Florine atoms you should be comfortable with doing that the second skill you should be okay with doing is knowing how to convert atoms into ions so let's say if I had the sodium atom you can see that there's just one electron on the outermost energy level so you should be to predict that it's going to need to lose that electron in the case of the Florine atom you should be able to see straight away that it has 7 out of the eight maximum electrons in the outermost energy level so it just needs to gain one more to form an atom sodium's going to lose that one electron and here's the new bit if you've been wondering what happens to these electrons when they're lost or where these atoms gain their electrons from this is how it works sodium can lose that one electron and then give it to the Florine atom remember that once it loses that electron is called the sodium ion some of the onic symbols in their formula from the first 20 elements are as showing you'll notice that I've sorted them based on their charges and whether they're positive or negative positive ions are called catons while negative ions are called anons you'll also notice a few blank boxes that's because these are the other ions you need to be familiar with in ncea level one this layout here is called the table of ions this is given to you in the exam the bad news is that the names aren't so I'm going to go ahead and give those names to you now don't freak out because on the left you'll see that the cat ions have names that are just the same as their atoms it's only really the anons that have slightly different names for example instead of calling it The Florine ion it's called the fluide ion instead of calling it the chlorine ion it's called the chloride ion the other thing I want you to notice is that ion appears twice in the cations be careful here you want to make sure that fe2+ is called Ion 2 and fe3+ is called ion 3 I'm also going to go ahead and point one new thing out to you and that's the ammonium ion don't confuse this with ammonia ammonia is something else let's look at a first example of writing ionic formula for silver chloride to do this I need to find silver and chloride on my table of ions the next thing I'm going to do is that I'm going to compare their charges you can see that silver has A+ one charge while chloride has a minus one charge here's a little rule for you if you've got equal and opposite charges you can just write the symbols together this means I should have AG for silver and cl for my chloride therefore silver chloride can be represented as AG G before I go on I want you to notice something notice that my plus and my minus my charges are actually gone let's look at another example with rule number one let's say we had to write the formula for berium sulfate just like before we need to look for berium and sulfate in our table of ions just like before we're also going to compare their charges you can see that they have equal and opposite charges bariums got plus two and sulfate has a minus two when they have equal and opposite charges we're just going to write everything together so barium is going to be ba and sulfate is actually going to be just so4 notice that for my final formula I don't show the charges I don't show a plus two and I don't show the minus two either rule number two is that we're going to use multiples to make sure that opposite charges are completely balanced let me show you an example let's say I wanted to write the ionic formula for calcium chloride just like before I'm going to look in the table of ions for calcium and chloride again I'm going to compare their charges and you can see straight away that calcium's got A plus two charge which is not balanced with chloride which has a minus1 charge this means I'm going to need two sets of chloride so that my charges will be balanced when I go ahead and write the formula I'm still going to write C A for calcium I'm still going to write CL for chloride but because I need two lots of chloride I'm going to show a little two in the bottom right hand corner for my chloride in another example of using multiples let's say we had to write the formula for silver sufate we can see these on the table of ions and we're going to compare their charges again this time Silver's the one with the plus one charge and we need two sets of to balance out with the minus 2 charge from the sulfate when we write the formula I'm still going to stick down AG for silver I'm still going to stick down so4 for my sulfate but because I need two sets of silver I show that with a little two at the bottom right hand corner of AG in my final formula the final rule is that if I need multiple sets of a compound ion then I need to use brackets I've highlighted the compound ions for you but you can see that the compound ions are just ions which have more than one different type of element let's look at magnesium nitrate as an example we can compare their charges magnesium's got plus two when nitrate has minus1 straight away from rule two that tells you you need two sets of nitrate so that the charges will be balanced again when we write our formula I'm going to stick down mg for magnesium and NO3 for nitrate I needed two sets of nitrate so I show that with a little two but since nitrate is a compound ion I need to show that by using brackets around the entire nitrate