consider this problem what type of bonds are contained in the following substances is it ionic or covalent and if it's covalent would you describe it as being polar covalent or nonpolar covalent now before we tackle this problem we need to be able to determine the difference between an ionic bond and a covalent bond so how can we quickly distinguish the two let's say if we're given a test problem the first thing i recommend knowing is that an ionic bond is usually between a metal and a non-metal covalent bonds exist usually between two nonmetals and within an ionic bond an ionic bond occurs between ions and ions are particles that contain positive and negative charges covalent bonds basically they have partial charges if it's polar covalent if it's non-polar covalent then those charges are minimal now the second thing that you want to keep in mind is that covalent bonds involve a sharing of electrons whereas ionic bonds they are created by a transfer of electrons and later in this video i'm going to explain these concepts but let's see if we have enough information to answer this particular question so let's understand part a or let's uh answer it br2 what type of bonds are contained in that substance so br2 is bromine and it looks like this so you have a molecule which is composed of multiple atoms in this case this molecule has two atoms and within this molecule you have a single bond and each atom has three lone pairs so that's how the bromine molecule looks like but now let's describe the bond that holds these two atoms together is it ionic or covalent so do we have two nonmetals or is this a metal mixed with a nonmetal well you need to know where the metals and the nonmetals are located in the periodic table to answer that question in the first place and so let's take a minute and talk about that so if you go and get your periodic table or if you don't have one go to google images and look for the following elements they should be in the upper right side of the periodic table and you're going to see this line that divides some of these elements now most of the elements located near that line are known as metalloids or semiconductors a metalloid has properties that are in between a metal and a nonmetal but what you want to take from this is that the nonmetals are located to the right of that line and to the left of that line you have the metals so by using the periodic table you can quickly determine if an element is considered a metal a non-metal or if it's on a line a metalloid so bromine is on the right side of the periodic table therefore bromine is considered a non-metal so here we have two nonmetals mixed together and because those elements are the same the two electrons that are in this bond will be shared equally between uh those two atoms and so we're going to have a covalent bond so anytime there's some sort of sharing of electrons you have a covalent bond now that we have a covalent bond we need to discuss is it a polar covalent bond or is it a non-polar covalent bond in a non-polar covalent bond the electrons are shared equally if it's polar covalent that means that the electrons are being shared between the two atoms but relatively unequally so in this case this is going to be a nonpolar covalent bond because the elements are the same in order for it to be a polar covalent bond the elements have to be different so let me just give you some notes on this so if it's going to be polar covalent the electronegativity difference has to be 0.5 or more a nonpolar covalent bond has an electronegativity difference value of 0.4 or less so just keep that in mind now let's consider methane ch4 here's the lewis structure of methane and we're going to focus on the carbon hydrogen bond so this particular bond is it ionic or is it covalent what would you say and let's compare that bond with the bond between two hydrogen atoms now automatically if the elements are the same in a chemical bond then you know it's going to be a nonpolar covalent bond but if the elements are different it could be ionic or it could be polar covalent or it could be even non-polar covalent but first let's see if it's ionic or covalent so carbon is it a metal or is it a non-metal what would you say carbon is considered to be a non-metal it's on the right side of that line hydrogen even though it's on the left side it's not really considered to be a metal it's considered to be a non-metal so be careful with that one so here we have two nonmetals combined so therefore we know that this is a covalent bond now is it polar covalent or is it nonpolar covalent answer that because the atoms in that bond are different we need to look at the electronegativity values here are some common values that you want to be familiar with the electronegativity value for hydrogen is 2.1 for boron it's 2.0 for carbon 2.5 nitrogen is 3.0 and then oxygen is 3.5 fluorine is 4.0 it's the highest and then we have chlorine which is 3.0 bromine 2.8 iodine 2.5 and you can look up these values if you go to google images and type in electronegativity values it should come up so in the ch bond the electronegativity difference between the two elements is 2.5 minus 2.1 which is 0.4 so therefore the bond is considered to be nonpolar if the elements are the same then the en difference will be zero which means it's definitely nonpolar so both of these bonds are nonpolar covalent bonds now let's move on to part c so what type of bond do we have between the elements carbon and oxygen what would you say is it ionic or is it covalent well carbon is a nonmetal and oxygen is a nonmetal so we have two nonmetals which means that the bond in between them is covalent rather than ionic now to determine if it's polar or nonpolar we need to look at the electronegativity values carbon has an en value of 2.5 and oxygen is 3.5 so the electronegativity difference between the two elements is 1.0 which is greater than 25 so therefore this particular bond is a polar covalent bond and that's basically it that's how you can quickly tell if it's polar covalent or non-polar covalent and it's by looking at the en difference values now let's move on to lithium fluoride is it ionic or is it covalent well lithium is on the left side of the periodic table so it's a metal in fact it's an alkali metal fluorine is on the right side of the table it's a halogen which is a type of nonmetal and so here we have a metal and a nonmetal when you see that that tells you that you're dealing with an ionic bond now let's go deeper into ionic and covalent bonds let's understand how they're made now let's start with ionic bonds before we go back into covalent bonds lithium as an atom has one valence electron fluorine as an atom has seven valence electrons fluorine as a nonmetal has a very high electronegativity value it's 4.0 and lithium as a metal has a very low electronegativity value which i don't remember what the number is but it might be like 1.0 or less but it's pretty low and because fluorine is more electronegative it has a strong affinity for electrons it really wants it and the halogens they like to have eight electrons to satisfy the octet requirement they want eight electrons in their outer energy level to be stable to be satisfied and so what you need to understand is that metals they like to give up electrons and non-metals like to take them so what's going to happen here is we're going to have a transfer of electrons so lithium is going to give up it's one electron to fluorine and so when lithium loses that one electron it's going to acquire a positive charge when fluorine gains that electron it acquires a negative charge now what do you know about opposite charges if you have a positive charge next to let's say a negative charge what will the two do well opposite charges attract and so you're going to have a force of attraction and this force keeps them together so this is the chemical bond between these two ions it's called an ionic bond so that electrostatic force of attraction is what holds the ionic bonds together now let's consider the situation in a covalent bond and let's use bromine as an example so bromine as an atom has seven valence electrons like fluorine and because they're in the same column group seven a of the periodic table they're both halogens and as a result they both want eight electrons when a bromine atom meets up with let's say another bromine atom both of them they want to have eight electrons but none of them want to give up their electrons and so they're like how are we going to figure out the situation i need an extra electron and you need an extra electron what sort of deal can we make so that we both get what we want in this case what they do is they share electrons and so bromine it gives up one electron to form a bond and the other bromine atom gives up one electron as well and keep in mind it takes two electrons to make a bond and so we get the bromine molecule which looks like this and there's a single bond between them so each bromine atom now has eight electrons around it so if we look at the bromine atom on the left two four six and this is considered two so that's eight electrons the same is true for the one on the right it has two four six and the two shared electrons so it has eight and in this arrangement they satisfy the octet requirement that they have that is to have eight electrons in their outermost energy level now because the electronegativity of the two atoms in this molecule is the same the electrons are shared equally and so this is going to be a nonpolar covalent bond now let's talk about the other situation a polar covalent bond and in this video we use the example of carbon and oxygen so carbon as an atom has four valence electrons oxygen as an atom has six valence electrons now both of these are nonmetals and as a result they want to acquire electrons so like in the previous example they need to make a deal they need to share electrons so that both of them can have eight the question is how are they going to do it in this case they're going to share electrons unequally for this to work carbon is going to give two electrons to make a bond between carbon and oxygen but oxygen is going to give four electrons and so we have a total of six shared electrons and if you recall it takes two shared electrons to make one bond so six electrons will make a triple bond the lewis structure between carbon and oxygen it looks like this so those are the six electrons that were used to make that bond so carbon gave up two which means that it has two electrons left oxygen it gave up four which means it also has two left and so this is the lewis structure for carbon monoxide carbon has an electronegativity value of 2.5 and for oxygen is 3.5 and because oxygen is more electronegative than carbon it's going to pull the electrons in that bond closer to itself so oxygen will acquire a partial negative charge and so you have this delta looking symbol for partial charges and uh carbon because it has a lower electronegativity value relative to oxygen it's going to be losing some electrons to oxygen oxygen is going to pull those electrons more close to itself there's both of them are still sharing electrons but what we have is an unequal sharing of electrons and due to this unequal sharing one element pulls on the electrons more than the other one does and because oxygen has a greater pull it's going to have a partial negative charge whereas carbon is going to have a partial positive charge and when you have these partial charges in a covalent bond it makes it a polar covalent bond when something is polar it means that it's still neutral overall but it's polarized one side has a partial positive charge and the other side has a partial negative charge and that's what it means for something to be polarized you have a separation of charges in something that is intrinsically neutral because overall this is a neutral molecule if you add plus one and negative one you get 0. but you have a spread of partial charges within this individual molecule and so this is a polar covalent bond so what i'm going to do now is make a summary of what we've just considered so we talked about ionic bonds and we talked about covalent bonds now within a covalent bond you can have two types it can be a polar covalent bond or you can have a nonpolar covalent bond so for the ionic bond we have the example of lithium fluoride now in an ionic bond you have ions lithium has a positive charge fluorine has a negative charge in a polar covalent bond we had molecules like carbon monoxide however we didn't have a full charge but we had a partial charge carbon was partially positive and oxygen was partially negative so make sure you see the difference in ionic bonds you have full charges like a plus one or minus one whereas in a polar covalent bond you may have partial charges they could be 0.1.2 but it's not a full charge in a nonpolar covalent bond as in the case of the bromine molecule the electrons in this molecule were shared equally and so there are no partial charges and if you recall ionic bonds are typically made up of metals and nonmetals whereas covalent bonds they typically consist of two nonmetals be it polar covalent or nonpolar covalent and remember the en difference for a polar covalent bond has to be 0.5 or more for a non-polar covalent bond it's usually 0.4 or less so that's basically it for this video that's a summary sheet of what i have and there's one more thing i do want to mention ammonium nitrate this is one of those exceptions you need to watch out for would you consider it to be ionic or covalent now looking at the elements nitrogen hydrogen and oxygen you'll probably notice that there are no metals in this example so you might be thinking this is a situation between two nonmetals which it is however it's not you can't rule out ionic bonds in this case because it turns out that this compound has a mixture of ionic and covalent bonds ammonium is a polyatomic ion with a positive charge and nitrate is a polyatomic ion with negative charges so between the ammonium ion and the nitrate ion you do have an ionic bond even though there's no metals so this is one of those exceptions where you have an ionic bond between two nonmetals so when you see a metal and a nonmetal that's typically an ionic bond if you see two nonmetals usually it's a covalent bond but it could be an exception as you see in this case now for this particular substance ammonium nitrate we do have covalent bonds within the polyatomic ion so within the ammonium ion which looks like this the bond between hydrogen and nitrogen is a covalent bond it's a polar covalent bond the ian difference is more than 0.5 the electronegativity value for nitrogen is 3.0 for hydrogen's 2.1 and for the nitrate ion which looks like this we do have another polar covalent bond between a nitrogen and oxygen the en difference is 0.5 so within this one molecule you have both ionic bonds and covalent bonds so there are exceptions you need to watch out for them but the things that were mentioned in this video are general rules to keep in mind