Writing Chemical Formulae

[00:00:00]so in the second of our introduction to chemistry videos we're going to look at writing different types of chemical formula so we will start with molecular substances so they're covalently bonded substances now we're going to move on to eye on eclis bonded substances and we're going to look at the different types of formulas that we've got to be able to write so for molecular substances there's a bit more memory work because not as much working out it's more to do with remembering the formula so one of the things I want you to try to remember is the formulas of all the diatomic elements to know whether they're going to exist as an diatomic or monatomic going around on their own so if you go back to the video on the periodic table you should be able to remind yourself about the formulas of the elements so on the left hand side here we've got elements and on the right hand side we've got some compounds but these are all molecules so on bonded in some way so oxygen is one of our diatomic I have no fear of ice phobia this is the off and the diatomic elements right hydrogen h2 fluorine CL 2 nitrogen n2 whose only two other diatomic elements that there are one of them a theobromine and the last one would be fluorine and then just if you remember we recalled when we were looking at our parent table that phosphorus is another element that goes around but this time in force p4 and the worst one boy if you want to stick that on the bottom you could add sulfur onto the bottom here as well we had that one remaining diatomic element fluorine there are elements though in molecular our compounds so we've got water hopefully everybody knows the formula of water is h2o what's the formula sio2 follow we should all know that and x3 is ammonia my end of that word is quite important because something called ammonium later with a different formula ammonia nh3 ch4 you all have used at school that's me thing if carbon dioxide is co2 carbon monoxide mono meaning one CO and sulfur trioxide tri meaning three is that's a three sulphur dioxide with the so2 you need to learn these formulas what about the acids that you might come across so pause the video now and see how many of these I said you actually know from the top of your head there you go so we would hope that you know the Farmers of hydrochloric and sulfuric acid but perhaps you are not as familiar with nitric nitric here two or three phosphoric acid again not as commonly used at GCSE so you might not be familiar with that but that's a ch3 po4 so make a priority to learn the formulas of these acids you might want to move on now and write those formulas on to your dr2 sheet that you carry around with you at all times so that you've got them they're handy if you were to forget them right down on your data sheet the formula if some is now when we were looking at our periodic table in an earlier section we didn't mark on the charges of these ions on a periodic table but group on metals lose one electron to become one plus iron so some examples of that would be sodium becomes a sodium plus iron lithium becomes Olivier Messiaen potassium becomes a potassium one force I in group 2 metals lose two electrons there to our shell electrons become two plus ions like magnesium calcium barium those things in group seven their nonmetals they gain want to like trying to get a full shell of electrons so we're talking things like chlorine becoming the chloride iron bromine becoming the bromine iodine becoming the iodide iron notice that for positive ions we don't change the name so sodium becomes a sodium iron we just say sodium iron magnesium becomes a magnesium iron but for the nonmetals chlorine becomes chloride and when it ends IDE it means it's a negative ion of the element chloride bromide iodide group six oxygen becomes oxide and they become 2 minus because they're going to electrons sulfur becomes sulfide so sulfide x2 minus man you might have heard of sulfate at school you might use copper sulfate when it says a te it's not just one element it's made of soft for an oxygen sulfate so sulfide is just sulfur and sulfate is sort of a-- and oxygen and then there's the little section in the middle of the parent table that's a little bit confusing because it's not in a group so you think how many electrons does it lose and I'm not the reason those metals in the middle are their areas because they can form more than one stable iron it can lose different numbers of electrons and forms their volumes and so we're going to use Roman numerals if you aren't familiar with the Roman numerals up to 7 you need to practice the Roman numeral III IV V VI and VII you just need to be able to go to seven in a level chemistry copper 2 is telling us the two in Roman numerals is telling us that the charge on complex is a 2 plus I in 3 he is telling us that the charge on iron is Fe 3 plus when we see them ni 2 plus we would write the Roman numerals are always positively charged and numbers because their transition metals only form positive ions metals always lose electrons to form positive ions then we're going to need to learn the formula of some compound I remember that their definition of a compound is two or more after different atoms chemically joined these ions are made of two or more different atoms chemically joined all of these compound ions you need to know the formulas off so again if it's gonna help you you could write them onto the front of you dare shoot there's a big empty space on the front of the dirty sheet you could write these on so that you never forget them we've got the positively positive one you need to know it's called the ammonium remember the previous section I highlighted ammonia and made a point of saying ammonia now we've got ammonium and that's NH 4 plus ammonia is nh3 ammonium nh4 plus got hydroxide nitrate and hydrogen carbonate there are 1 minus and carbonate which is 2 minus and sulfate and phosphate which is three minus you've got to learn these so how would you put all that information together to work out the formula for an ionic compound remember we've learned the formula for our covalent compounds we can work out the formula for our ionic compounds so you read the name magnesium chloride and you write down the formula the two items of magnesium you set yourself on my Museum it's in group 2 of the periodic table and therefore I know it's going to follow me to the bus iron and then chloride comes from chlorine chlorine is in group seven of the periodic table and things in group seven form a1 minus iron now you balance the charges that needs to be the same amount of positives as there are negative so to do that we've got two pluses we're going to need two minuses so we'll need two chloride ions to balance and magnesium I'm gonna have mg co2 and that too comes down there as a subscript to chloride ions so pause the video and see if you can work out the formulas of each of these three ionic compounds you go sodium is in Group one so sodium 1 plus iodide is one minus one plus and one minus balanced so the formula is just nai calcium is in group 2 so it's 2 plus and fluoride is what - so I end up with CAF two aluminum's in group 3 an oxide is in group 6 so I've got 3 + 4 2 - now to make those balanced I'm finding a common multiple and the common multiple is 6 so 2 threes milk 6 I'm 3 2 X 6 and we're balancing out the charge al2o3 aluminium oxide now what we need to do is watch out for those compound ions those ones that we've had to learn tightens the periodic table to find so if we're doing this we've got copper 2 so the Rose tells about the copper and sulfate we have to memorize is a sulfate is so4 2 - item and then we check if the balanced charge is balanced they do so we write CU x to the 4 so again pause the video have a go at these for here see if you can work out their formulas okay so have a look at those sodium carbonate na2co3 now not somebody some Ernie and one we've got an ammonium ion which is one plus and the sulfates - - so we need to ammonium ions to balance the sulfate but we can't write n h42 have to have two of the ends and to lots of the hitch for as well as we have to put in brackets when we've got a compound I am with more than one actor no we want to double it then we need to put that in brackets similar thing happening here with the magnesium hydroxide - hydroxide ions and again with the hydrogen carbonate I need two hydrogen carbonate often students make a mistake here and they think they have to put calcium and their net to try and work out hydrogen and then they have to try and work out carbonate ionic compounds are made of two ions a positive ion and a negative ion - just need to find the positive iron calcium and everything else is the negative ion hydrogen carbonate magnesium is the positive ion hydroxide is the negative ammonium is the positive sulfate is the negative losing you just need to be able to figure out the positive and the negative and put them together balancing the charges