this lecture is about ionic bonds ionic bonds are one of three categories of bonds we're going to discuss in this class we've already talked about calent bonds both non-polar and polar calent bonds now we're going to talk about ionic bonds and then after that we're going to talk about hydrogen bonds ionic bonds are an attraction between ions of opposite charge and I'll talk about how those ions form during this quick lecture and we will also talk about some other things related to electron negativity which is going to play a role not only in ionic bonding but we already talked about how electro negativity plays a role in calent bonding and it will also play a role in hydrogen bonding so ionic bonding occurs between ions of opposite charge remember that opposite charges attract so when we say opposite charge we mean positive and negative again I will talk about how those ions form what an ion is in a couple of minutes it's also important to note that ionic bonds occur between metals and non-metals if you look at the periodic table there's this sort of staircase shape that separates the metals from the non-metals and that's not hugely important to know in this class which elements are metals versus non-metals but it is important to note that ionic bonding involves this so everything in red are metals which really shows you that most elements on the periodic table are Metals everything in blue those are the non-metals we're going to use sodium and chlorine as our example today and you can see that sodium on this periodic table is a metal over there in column one and then chlorine over in column s is a non-metal this story as I already mentioned is also going to involve electr negativity so just a quick reminder about what electronegativity is it is the pole an atom has on electrons so if an atom has a high electr negativity that means it has a strong pole on electrons if it has a lower electro negativity it means it has a lower or less pole on those electrons a weaker pole this is going to to play an important role in a lot of things we talk about this semester cellular respiration hydrogen bonding we already talked about how it plays a role in Co valent bonding so electr negativity is a really important concept to understand and as you'll recall there's a trend on the periodic table in which the electro negativity increases as we move from left to right and from bottom to top on the periodic table so everything in that upper right corner has a high electr negativity now remember there are few elements in column 8 that don't really play a role in this story because they have a full outer electron shell they're not really trying to attract electrons because they don't need to to fill an outer electron shell but each element really has an electro negativity rating that I don't want you to concern yourselves with in this class but when two atoms have a big difference in electronegativity they're going to tend to form ionic bonds and we're going to see how today when we go through this story so electr negativity is going to play a role let's first talk about how ions occur and again I'm going to use sodium and chlorine as our examples today let's start with sodium looking at the periodic table sodium is atomic number 11 and as you'll recall that atomic number represents the number of protons that an atom has in the nucleus and the number of electrons that that atom has so sodium atom has 11 protons which are positively charged and it has 11 electrons which are negatively charged so remember in every atom on the periodic table the number of protons equals the number of electrons which means that those atoms have zero net charge and again this is a sodium atom that we're talking about now let's look at chlorine chlorine is atomic number 17 that means of course that chlorine has 17 protons which are positively charged and 17 electrons which are negatively charged so once again chlorine has zero net charge just as all atoms on the periodic table have no net charge let's look though at the electron configuration for each of these atoms now remember that the veence shell is the outermost elect shell of an atom and every atom needs a full outer electron shell to become stable so that's review every atom needs a full veent shell which is that outermost electron shell to become stable if it doesn't have a full outer electron shell it's going to do something to fill it we already talked in calent bonding about how two atoms can share electrons to become stable today we're going to look at a different option that atoms have in certain circumstances not all atoms have this this situation occurring they don't all have this option but sodium and Chlor sodium and chlorine do have this option so let's look at the electron configuration of sodium I'm going to just write the chemical symbol for sodium in the nucleus we're not concerned about the number of protons or neutrons in the story this story is really concerning the electrons remember that this first electron shell that's closest to the nucleus I'm just going to draw the nucleus really small here has two spots available for electrons then the second electron shell has eight spots available and then the next electron shell also has eight spots available sodium is atomic number 11 which means it has 11 electrons and let's draw those first two are going to be in the first electron shell 2 + 8 is 10 sodium is atomic number 11 so that means it has a one electron in this outer electron shell we also know that it has one electron in that veence shell because it's in column one so that would be the shortcut let's now look at at chlorine sorry let's look at chlorine okay nucleus now first electron shell two spots next electron shell sorry I should have drawn that a little smaller eight and then third also eight so chlorine is atomic number 17 that means 2 + 8 is 10 that means chlorine has seven electrons in that outer electron shell also chlorine is in column seven so that's the shortcut for knowing the number of veence electrons that chlorine has neither of these atoms have a full outer electron shell sodium has seven spots available that it needs to fill to become stable chlorine only has one open spot that it needs to fill to become stable for sodium to share seven pairs of electrons would require a tremendous amount of energy input it's not possible for that to happen there's not enough energy available for that to happen instead something else occurs when sodium and chlorine come in proximity to each other chlorine is very electronegative it's in the upper right corner of that periodic table it has a very high electro negativity meaning it has a strong pull on electrons sodium has that one electron in that outer shell all by itself so when chlorine comes in proximity to sodium it is going to steal that electron from sodium and that electron is going to fill the outer electron shell for chlorine so the chlorine now has a full outer electron shell sodium gave that electron away it doesn't have it anymore in fact once that electron's gone it doesn't have that third shell anymore either so now sodium has a full outer electron shell because that second shell becomes its veent shell and it's now full so both atoms now are stable but guess what they're not called atoms anymore and the reason for that is they no longer have an equal number of protons and electrons they are no longer electrically neutral let's look at what happened to sodium first so sodium did have 11 protons and 11 electrons the number of protons cannot change if that changed it would be a completely different at because that is what defines the atomic number of the atom and what type of element we're looking at so sodium still has 11 protons but it gave an electron away to chlorine so you can either say 11 minus 1 is 10 or you can just count that there are 10 electrons now shown on that electron configuration diagram of sodium so it now has 10 electrons now they're no longer equal so sodium now has a net electrical charge of + one because it has one more proton than it does electrons they're no longer equal this is now what we call a sodium ion and it's written with a superscript plus remember in chemistry we don't write a plus one or we don't write a one next to something in a chemical equation where there's just one if something's written alone it implies the number one if it had a plus two charge or a plus three charge we would write that number for one we just write the plus let's look at what happened to chlorine chlorine atomic number 17 17 proton 17 electrons it gained an electron so it's still going to have 17 protons but now it gained an electron you can either do the math or you can count that that's now 18 negatively charged particles so now there's one more electron than protons which is going to give this a minus one charge it's now what we call a chloride ion and we write that as a superscript minus again again we don't write the one if it was a minus two we would write the two but because it's a minus one we just write the minus sign now these are what are called ions and they are now weakly attracted to each other due to that opposite charge attracting so the way that looks is sodium ion and chlorine ion come in contact with each other and through ionic bonding attraction between ions of opposite charge they are now going to form the compound which is what we call when two ions come together through ionic bonding we call this a compound and this compound is called sodium chloride otherwise known as table salt this is the salt you get in a salt shaker so attraction between ions of opposite charge that plus one and minus one cancel each other out when they're connected together so it's almost like this they're not connected like this in calent bonding they're sharing electrons they're really tightly connected this is more an attraction between these two separate atoms sorry I kind of look like something weird happening right now on the video but you get what I'm saying so attraction between ions of opposite charge sodium and chlorine come together to form this compound also important to note that when this is mixed with water you're going to see when we talk about properties of water these two are going to separate back into ions again so this sodium chloride would not occur in a solid form in the body when it's mixed with water it dissolves and you know that because you know you can mix salt with water and these ions in the body are going to play a very important role in our physiology that we will talk about when we discuss properties of water we will talk about these ions when we talk about transport across cell membranes so ions are really important to understand in an ion the number of protons and the number of neutrons are not equal so ions number of protons does not equal the number of electrons and there is a net electrical charge positively charged ions are called cat ions I always think that's kind of funny because I think of cats as not being so positive all the time that's not what it means it's not talking about the animal a cat and negatively charged ions are anion so really an ionic bond occurs between a cion and an anion this doesn't just occur between sodium and chlorine if you take a higher level biology class or chemistry class you you can look at more details of what other elements come together but it's always a metal and a non-metal and so in other words it's always something really Electro negative coming together with something that's not as Electro negative so there's a really big difference in electro negativity between two atoms so something in column one something in colum seven they're going to tend to form an ionic bond so that is ionic bonds