this is an example of lewis dot structures so the first one is the lewis dot structure for a neutral atom and this one on the right is the lewis dot structure for the three minus anion so this would be basically looking at anything in group 15 and turning it into a -3 anion which would get it to noble gas configuration where we have eight electrons so these dots each represent a valence electron and this is kind of what lewis came up with in the first place so this is named after a guy named lewis uh and he drew these little little dots uh basically around a cube that is centered around the the atom and he he drew these little dots and this is what they've become over the years is these dot symbols so this tells us how the elements and the ions form compounds because if we have this element and it forms this ion it is not really going to bond with anything but if we have the element by itself it's looking for three more electrons so it has five and it's looking to get those three from somewhere else so one way that it would get those electrons is by bonding with something that has three electrons so for example we could have um anything in group 15 bonding with things in group 13. those are called covalent compounds because they're made up of both non-metals and those we'll get to a little bit later in the chapter but the ones that we're talking about the ones that we're going to talk about in the beginning of chapter 5 are ionic compounds which are always a metal so group one or two and a non-metal all the stuff on the right so s block and p block and this is what that ionic bond looks like it's this plus one metal uh cation bonding with a minus one non-metal anion and the bond is formed based on coulomb's law so there's attraction between the different charges and basically ionic bonding is a transfer of electrons so we can write it out like this that sodium we ionize the sodium atom so that we get so this is where that ionization energy comes in and we end up with a sodium plus ion and an electron but that electron is going to be joining the chlorine uh atom to become the chlorine ion in which case we'll have a positive and a negative both so together they have eight electrons and they form a neutral compound so one positive one negative adds up to zero so we get a neutral compound and these are called binary compounds if they are composed of one metal cation and one non-metal anion so they're binary there's just two things involved and these ionic compounds are pretty much always found as solids with this lattice structure so it's a 3d structure of the compound where we've got alternating sodium and chlorine ions in our crystal and we can then talk about the lattice energy of these ionic solids where they are going to which is basically the amount of energy required to break this solid apart into its constituent ions so the formation of ionic bonds releases a lot of energy even though we don't really expect it to because ionization energy required to ionize sodium and the electron affinity released when we ionize chlorine when we turn it into an anion that combination of energy basically cancels out so the fact that we're releasing energy when we form these ionic bonds comes from the lattice energy comes from the energy required to break apart that solid into a mole of each type of ion so the higher the lattice energy is the more stable the structure is and the harder it is to break up into ions and we can compare lattice energies by looking at coulomb's law so coulomb's law it's this is the force version so we've got distance squared on the bottom the charges come from the charges on the ions the distance comes from the ionic radii of the ions so the distance that they're separated by is the sum of their radii so the nucleus uh is where the positive charge is held so the nucleus of lithium is an atomic radius or ionic radius away from where it meets iodine in this case and then the ionic radius of iodine is the distance is the additional distance away from the nucleus of iodine so we add those together for the distance between the two charges and you can compare the lattice energy based on the charges so in this case so in the bottom picture they're comparing increasing charge differences to compare the lattice energy in the top we're comparing increasing distances to compare the lattice energy so there's two places where we're going to see um a difference in the distance between the nuclei and in the charges themselves so the naming of ions and compounds is called nomenclature so this is something that chemists are very particular about is the nomenclature so especially if you go on to organic chemistry there's a whole naming system it's called the iupac naming system i don't remember what that stands for off the top of my head but it's a very particular way of naming molecules and compounds that uh is used throughout the world uh so just like our significant or sorry just like our scientific um units just like our si units uh that are used by everyone throughout the world the nomenclature for naming ions compounds organic compounds etc those are common throughout the world so that everybody knows what everybody else is talking about it's very important for sharing science which is one of the steps of the scientific method that we learned way back anywho main group cations when we're naming these the main group cations keep the name of their element and then we tag an ion on the end so potassium so k plus is the potassium ion calcium two plus is calcium ion aluminum three plus is the aluminum ion they um have the same charge all the time the group one group two and group three well group one group two and group thirteen ions always have well that's not true but group one group two and aluminum always have the same charge so we don't need to specify the charge anywhere in the name of the ion transition metal cations on the other hand which we talked about a little bit last time these transition metal cations they can come in different charges because of their unique electron configurations so we have to specify the charge of the ion using roman numerals and we keep the element name and add ion on the end so iron so fe2 plus is the iron ii ion fe3 plus is the iron iii ion they used to be called the ferrous ion and the ferric ion but we don't use that terminology anymore because it's definitely more well-known more commonplace everybody knows what you're talking about when you say iron two or iron three uh ferrous and ferric can get confusing because little known fact there's also an iron one plus uh ion that is possible and what do we call that don't know so that's why we use the roman numerals instead of the greek endings alright and then anions non-metal anions they change we change the element ending to iod and we add ion on the end again we always add ion on the end so the chlorine minus that's called the chloride ion o2 minus is the oxide ion so those are the endings we change chlorine to chloride we change oxygen to oxide we just change the ending and add ion on the end very simple and we have a nice list of all the different common cations and anions you don't need to memorize most of these um so aluminum is one that's always the same barium is based on its sorry barium is based on its group 2 placement so it's always 2 plus so you should be able to either memorize these or identify them based on the place on the periodic table but you don't need to memorize things like chromium three plus you just need to know that if you see chromium with the three in roman numerals that's the chromium three plus ion if you see copper with two um roman numerals in the parentheses that's copper 2 plus ion so you don't need to memorize these per se but you just need to know how to read the naming of these ions you don't need to memorize that silver is a one plus uh cation that one's a little unique not one that you need to memorize per se but it's always the case that it is silver plus and then all of our anions their charges come from where they are on the periodic table as well our halogens are all uh one minus anions um nitride is a three minus because it's in group 15 so 15 minus 18 gives you minus 3 for the charge oxide is 16 minus 18 gives you minus 2 for the charge same with sulfide 16 minus 18. so this is just some common cations and anions for you to recognize all right and then we talked a little bit about this in class on monday so i was saying that potassium bromide is how you would name the kbr so the formula is kbr there's one potassium ion one bromide ion and when we combine them we call them potassium bromide and that's based on the charges a plus one and a minus one gives us a neutral charge of zero on our compound zinc iodide we've got the zinc two plus ion and the iodide one minus ion they combined form zinc iodide zinc has a two plus charge and iodine has a one minus charge so we need two iodide ions to balance out the plus two on zinc so we multiply it by two and that's where we get our little subscript in the formula so the formula is zinc iodide with a little two subscript and that takes care of our charge so the charges add up to zero and then aluminum oxide is a little more uh complicated because we have a plus three charge and a minus two so now we have to find uh the common denominator or the common uh multiplier i would say but the easy way to do it is to just move the charge on the cation to the subscript of the anion so plus three of the charge on aluminum goes to a three in the subscript for oxygen o2 minus the two minus ends up as a2 in the subscript for aluminum so we have two plus three aluminum ions in our formula and that gives us plus six we have three minus two oxygen ions in our formula that gives us minus six so together we get a neutral uh charge of zero on our compound and our formula is al2o3 for aluminum oxide so we could write some formulas for these ionic compounds you can pause here and write these formulas so these are all going to be based on the ions so aluminum ion is our al3 plus fluoride ion is a halogen so it's an f minus so i'll write these out for you uh copper with the two in the roman numerals is copper two plus and the chloride ion chloride is again a halogen so it's a one minus uh iron is that v and it's got a three here so that makes it a three plus ion and oxygen is a two minus it's in group 16. uh okay sodium we've got sodium is a group one uh what's the word main group metal ion so it gets a plus one charge and phosphide is in group 15 so the uh common way of finding the charge is 15 minus 15 minus 18 so we got a minus three charge on phosphide and then calcium is group two so we get a two plus charge and sulf sulfur or sulfide ion is right below oxygen so we end up with a two minus so when we combine these we have plus three so we need three of these to balance it out so positive 3 plus 3 times minus 1 gives us a neutral compound so that's a l f 3. um copper has a 2 plus so we need two chlorides to balance it out so plus two plus one times mu or sorry two times minus one gives us a zero so we write that one as cu cl2 and all right so iron three plus and oxygen two minus this one's going to be like our aluminum oxide on the previous slide so this one's going to be fe 2 o 3 so that the 3 ends up as a subscript for oxygen the 2 ends up as a subscript for iron okay sodium so now we have the opposite problem we have a small positive charge and a big negative charge so we need to do the same thing now we need three positive sodium ions to balance out the negative three charge on phosphide so we'd write this one as na3p we have three sodium ions and one phosphide ion and then calcium and sulfide oh we got a plus two and a minus two so that one is actually going to be cas and we don't need any subscripts on that one because plus two minus plus two plus minus 2 equals 0. so we don't need to change anything there it's the one-to-one uh ratio our formula all right and then naming these compounds is pretty easy so sodium plus the bromide ion gives you sodium bromide calcium plus the fluoride ion gives you calcium fluoride lithium plus the nitride ion gives you lithium nitride and sodium plus the sulfide ion gives you sodium sulfide uh the compounds so when you have uh our transition metals we just keep that roman numeral again so now we've got iron ii the iron ii chloride or iron three chloride respectively and all of that is summed up in this flow chart over here okay awesome let's keep going oh so now we can name the ionic compounds that we just made before so we've got aluminum and fluoride so that's going to be called aluminum fluoride we've got copper ii and chloride that's going to be called copper ii chloride we've got iron three and oxide so that's gonna be iron iii oxide you see where i'm going with this naming ion sorry naming ionic compounds is super easy once you know the names of the ions themselves okay finding the formula is a little harder but you just have to remember what the charges are based on the group of the metal cation or the group of the uh non-metal anion to remember what the charges are then you just got to make them cancel out gotta make them add up to zero polyatomic ions are ions that are composed of covalent bonds so these are multi-atom or poly atomic atom or polyatomic ions so we have more than one type of atom making up these ions and i've circled slash put boxes around the ones that i think are particularly important for you to remember um these are the ones that will come up a lot not that you won't see the other ones but i won't make you memorize the other ones i will definitely make you memorize most of these so ammonium ion nh4 plus hydroxide ion oh minus cyanide ion is cn minus the acetate ion which i will almost always write as c h 3 c o o and that's one of those structural formulas that i mentioned briefly in my previous video that tells us about the connectivity of the atoms so the acetate ion actually looks like this it's got a carbon with three hydrogens on it just like it says here attached to another carbon which has two oxygens and then that oxygen has a minus charge minus one charge all right so there's also the sulfate ion like copper sulfate for example is something composed of sulfate there's phosphate so one of the chemicals that i worked with like extensively in my research was silver phosphate so i am a big fan of the phosphate ion there's also the nitrate ion i also worked a lot with sulfur nitrates so another big fan of the nitrate ion and then these uh these two you won't see as often but they might come up is chlorates or perchlorate ions and those we'll talk about in a few slides those are unique because they have just differing numbers of oxygen so those are called oxo anions and we'll talk about those in a little bit the carbonate ion that one is pretty good to remember because you'll see sodium carbonate or sodium bicarbonate which is this one down here which is baking soda sodium bicarbonate but carbonate you'll see a good number of times calcium carbonate is lime it is basically what makes up um limestone and then another fun one to remember this one's not as important to remember but it's a it's a fun one it's the permanganate ion that one makes a solution that is bright purple which is pretty fun alrighty so when we're making ionic compounds using these polyatomic ions we're going to use kind of the same system that we use to make the formulas for the other ionic compounds with monoatomic ions so ionic compounds have a formula containing a certain number of cations and anions we always write the cation first and that is just the name of the metal pretty much and our charges have to add up to zero so this is the formula for calcium phosphate calcium phosphate is in your bones um this is the formula for calcium phosphate so the subscript tells us that they're the number it tells us the number of calcium ions the subscript over here tells us the number of phosphate ions so remember this whole thing is one ion so that is the same way that we had like calcium chloride before if we had calcium chloride now we're putting a polyatomic ion in there so that polyatomic ion has to stay together and that's why we use these parentheses when we're writing uh polyatomic ions with subscripts so i'll erase that so you can see the parentheses better so that means there are two phosphate ions in this molecular formula so we need the parentheses around it because if you don't have the parentheses it's going to look more like calcium with a subscript of three and then po42 and that's not what we want we don't want 42 oxygen atoms we want two phosphate ions okay and that's what the parentheses are for they're very important so uh how do we know that this is the right formula for calcium phosphate calcium is in group 2a or 2 as we write it now so that means it has a plus 2 charge as we see down here uh phosphate is a polyatomic ion with a minus three charge so you're just going to have to memorize those unfortunately so we'll go back to that slide phosphate is right here has a minus three charge so you're just gonna have to memorize what the names of the ions are and what their charges are they're always the same uh they don't change these polyatomic ions always have the same charge um that is written here in this table anywho phosphate is a polyatomic ion with a minus three charge to make the neutral compound we need three calcium ions and two phosphate ions so this is kind of the same thing that we did with the aluminum uh low is it aluminum i don't remember what it was aluminum oxide i think uh in the ionic compounds slides so now we've got calcium two plus and phosphate which is po4 three minus so we do our little squiggly arrow thing and that's going to be the subscript for our phosphate so you've got to put it in parentheses so there's a 2 with the calcium so now there's a 2 of the phosphate then we take our three and we put it with our calcium so we just do the same thing with the charges and the subscripts that we did before if you need to check which you should always check you can do that so the subscript the three times the charge on calcium plus two so that gives us a plus six uh the subscript which is two on the phosphate ion times the charge on the phosphate ion which is minus three gives us a minus six and if we add them together we've got plus six minus six we get zero perfect that's how we check to make sure that we have the right formula for our ionic compound all right let's practice so you guys can pause it here and practice on your own if you'd like but i'm just going to go through the answers real quick hopefully you got them so barium is uh in group two so it's got a two plus charge sulfate one of our polyatomic ions has a minus two charge so we got barium and we got sulfate and they cancel each other out so we got plus two and minus two gives us zero so we only need one of each so we don't need any subscripts we don't need any parentheses because we only have one of each all right what about this one ammonium ion nh4 plus and chloride ion so uh we've got a plus one and a minus one so those are the same as our barium sulfate we just put them together so we've got a plus one and minus one oops minus one so we get another zero so that is our neutral compound ammonium chloride uh we don't need any parentheses or any subscripts on our ions uh the subscripts are going to stay there that are part of the polyatomic ion we're not going to take those away um because that is an entity on its own it keeps the subscript because that is the definition of the ion all right let's try a different one we got sodium and carbonate so carbonate has a minus two charge and sodium has a plus one charge so we're gonna need two of those so we'll have sodium with a two and carbonate so that means we have two times plus one and minus two so that's plus two minus two equals zero perfect so you can do that with the little arrows if you want so the charge on carbonate goes to the subscript and the charge on uh sodium goes to the subscript but we don't write once so we don't need a subscript for carbonate and because we don't need a subscript for carbonate we don't need parentheses cool and last one magnesium and the hydroxide ion so oh minus is hydroxide all right so magnesium has a two plus charge it's in group two and hydroxide has a one minus so it's a minus charge so we're going to do the opposite of what we did with the previous one we're going to do magnesium and we're going to have two hydroxides so we took r2 we put it in the subscript took our one we don't write the subscript but it's kind of there it's implied so we've got a plus two plus two times minus one gives us zero so note this time i needed parentheses because magnesium hydroxide oops is not the same as saying magnesium oh h2 they're very different uh one exists and one doesn't really um so this is how we have to write it not like this we need our parentheses