there we go okay so again a brief look at ionic bonding and then we're going to be looking at covalent bonding which you guys actually already did if you have done the lewis structure lab and the valence shell electron pair repulsion theory lab so um that's down here and then uh this lab that i would assign monday or tuesday i would say you guys should get started on monday or tuesday it's not quite as long but it is such a critical lab so intermolecular attractive forces or imfs are going to be governing the chemical and physical properties of everything okay so why is something a liquid at room temperature versus a gas or why does some liquid like water dissolve something like ethanol but not something like oil right what's going on there it's all governed by ms why am i standing here sitting here talking to you and you can hear me because we have imfs that are governing basically the shapes of everything in our body the dna the proteins whether the protein is hair or nails or some kind of an enzyme that is causing reactions to occur right it's all about imfs and i think if there was one thing i would really want you guys to be able to take home that you will be applying in other classes particularly biology microbiology materials it is imf's so imfs we can't get to until we've gone through a whole host of things so lewis structures you have to know how to make them and then you have to apply best for theory and get shapes um and that's basically um what you started covering and we're going to continue to do that so um lewis bonding theory so early 1900s lewis is around and he is pretty much the jack of all trades he knows a lot about um adams and he publishes a book about bonds called the nature of the chemical bond and so he has a theory okay so remember our theory says why something is happening and this is early 1900s i want to say why the reason i'm bringing up this date is because according to lewis um theory uh there's no there's no quantum theory quantum theory quantum mechanics has not been um discovered yet okay so quantum mechanics doesn't get discovered that um until like later like 1920s and so yeah the whole theory of relativity hasn't been introduced yet so lewis is thinking about electrons as particles he's not really thinking about them as clouds he's thinking about them as particles and they can push against each other they can negatively repel they can be exchanged like money okay or they can be shared um between atoms in a covalent bond so it's either transfer or sharing now this is pretty black and white and what we realize is there's actually a continuation a spectrum of perfect sharing to not so perfect sharing like one atom has more electron density than another or more electrons are likely to be on that atom to electrons are transferred so there's actually um a continuation okay of whether an electron is transferred or is shared now he is the one who brought up the octet rule and if you have done the lewis structure lab you know that the octet rule has more exceptions to it than it does atoms that obey the octet rule basically the atoms that obey the octet rule are carbon nitrogen oxygen and chlorine and that's it hydrogen's a duet so is helium um boron will have six beryllium will have four we learned that ten has six okay so but the octet rule is very important because if you look at the atoms that are involved in life carbon nitrogen and oxygen right and then we've got some sulfur in uh cysteine which is an amino acid we have phosphorus which is right underneath right so we have phosphorus and sulfur phosphorus we'll follow the octet rule so for sulfur we'll follow the octet rule however they can also have something called an expanded octet and so the sugar phosphate backbone in dna the phosphate has two four six nine bonds around it okay um it doesn't it doesn't necessarily let's see two four six bombs around it instead of just four so it has uh an expanded octet and sulfur can have an expanded octet they might follow the rule they might not depends on the formal charges around the atoms so um if you're not don't know what i'm talking about uh watch those videos again and get a hold of me and come to office hour so lewis spawning theory is a great picture of lewis um he uh this is literally from his lab notebook here and what he's trying to do is trying to understand how these elements lithium beryllium uh born so he's going across the periodic table here right so this is element uh three four five and then underneath it right um is aluminum and then he's got carbon and silicon this is element six so he's going down the periodic table and he's saying well how what kinds of compounds do these bonds form or do these uh what kinds of bonds do these compounds form and how is this related to where it is on the periodic table okay and this is what he's looking at these are his notes he's thinking about in him to himself and he comes up with some ideas he theorizes that valence electrons are going to be used to explain bonding now there are many many theories for bonding and we are going to cover three of them lewis theory and vesper theory are merged kind of into one okay because vesper is part of lewis is bonding theory and lewis structures and then we have valence bond theory which is quantum mechanics so you have to remember chapter three and we have molecular orbital theory which is quantum mechanics have to remember chapter three there are other bonding theories out there there's crystal field theory which you'll get to if you look at transition metals okay lots of theories i want to say that most of the theories that i have seen um say that valence electrons are indeed the electrons that you want to think about when you're thinking about if it's going to be shared or if it's going to be transferred calculations have been done to include core electrons in the bonding theories and what has been found is that core electrons are so close to the protons that it takes too much energy for them to actually be shared or transferred so emphasizing valence electrons that part of the theory that lewis brought up in the early 1900s is similar across all three theories okay he drew models called lewis structures also known as electron dot structures which you have drawn and this is gonna allow us to predict many properties so we're gonna be able to predict polarity and polarity is um basically the difference in electron density on between two atoms or between overall molecule uh sizes okay and then molecular stability so will a molecule be stable or not like for instance why do we have h2o but not h4o right and we know that water yay favorite molecule here um is uh naturally occurring right all over the place but i've never seen h4o and why is that okay so we'll use lewis theory to look at that um and then from polarity you can get i am apps so one of the interesting things is that this theory bonding lewis's bonding theory has a lot of limitations to it and that's why new theories of bonding were introduced however it's extremely powerful in predicting a lot of physical and chemical properties of molecules still which is why you have to learn it and you will use it extensively when you get to organic chemistry so all of those are who are pre-bio anyone who's pre-med you have to know lewis structures like be able to make them in your sleep and explain them to you somebody who's never heard of chemistry before what is going on here um the tough part is that you get this in chem 1a you'll see in the beginning of chem 1b you'll do a little organic chemistry and then you don't see it again for like another six months and then boom there it is in your face again like whoa lewis theory okay so um this is one of the ones what is one of the things that you're going to want to highlight and maybe save for uh your first like maybe couple of weeks of organic chemistry for those of you who are going to be taking this class okay um so we're going to start out with ionic compounds um and for the structure of ions and remember you have ions that are going to be positively charged and ions that are negatively charged so the cation is going to have a symbol without valence electrons so the cation for um for sodium is just na plus and then anions are gonna have a symbol with eight valence electrons so if we look at chloride cl that's a symbol for chloride um it has if you look on the periodic table it has seven valence electrons seven valence electrons one two three four five six seven okay but if you add another electron to there plus one electron where did that one electron come from they came from sodium so remember sodium is going to become n a plus plus one electron if you start out with n a okay and then if i want to complete this like reaction um and i'm looking at ionization energy okay where does that one electron go well that one electron goes to chlorine to make chloride and um chloride chlorine has a high electron affinity it wants that electron so we'll take it and that's a high z effective and it will have a symbol that looks like this and typically we have brackets around it okay so i have some images on it so this is lithium fluoride okay um so this is lithium as the atom and then if you take one electron away okay you can add that electron to fluorine so here's fluorine the atom so that's f the atom a little line here and here is fluoride all the way to the right is fluoride the ion so this is a foreshadowing of redox reactions the atom has a valence electron on it we talked about the fact that according to the octet rule um and the stability of noble gases that electron would want to be given up and the fact that there's a low ionization energy for this to happen so um yeah sure why not lithium is reactive it likes to give up an electron chlorine is highly reactive it would like to take that electron and then you end up with lithium and fluoride now now that you have the positive charge of lithium and the negative charge of this ion you're going to make a compound and that is going to be lithium fluoride they're going to be strongly attracted to each other it is the strongest bond type that we have is an ionic bond um so let's look at some of the models um that that come out of the theory versus some of the observations that we see so um in lewis's theory the position of the ions in a crystal lattice contribute to stability of the structure so remember a couple slides ago i showed you pictures from his lab notebook of these little like looks like just boxes right and really what that was saying okay i've got some positive charges and then drawn in the upper right hand corner okay now the positive charges are going to repel each other but they're both going to be attracted to negative charges okay and so you end up with this kind of crystal lattice here sorry it's not erasing oh that erases way too much okay okay so every positive charge is going to be surrounded by negatives and this is what is meant by a crystal lattice if you've ever seen um like a lattice in a garden that looks like basically wood that looks like this right that's a lattice and um it's long-range crystalline order and this position of these ions is important um you don't want the positives repelling each other and the negatives repelling each other right so that would mean that if you tried to move the position of these it would be difficult and the ionic solid should be hard okay it meaning hard like i can't like a piece of butter i could put my thumb into it and just right um but an ionic solid um think of ionic solids that you know and some of the ionic solids that you know would be uh sodium chloride this table salt okay it is hard right have you ever tried to um break a piece of sodium chloride with your hand right you can't do it so um that's because you're trying to move the position of the ions you can do it without like a hammer or a chisel or something okay so that brings me to another um part it means that if you do break it okay or you do move the position then there's going to just be the shattering of the ionic solid it's going to be brittle so if you strike an ionic solid it will shatter and it will go and makes a lot of smaller pieces which is how a salt grinder works so you take this ionic solid you put it under pressure and enough pressure goes and it breaks and then you get smaller pieces of salt so do you see when i um put this arrow here now i have negative charges and positive charges aligned with each other these are all going to be repelling each other okay so along this um position they're literally just go pop and they're not going to want to be next to each other if you strike an ionic solid it will shatter so they are hard and they are brittle so the model and observation aligns another thing if you're going to try to conduct electricity you have to have a material that allows electrons to flow okay so that's the way electricity works right electrons flowing um but in an ionic solid the ions are locked in position okay they can't move around if they move around then they break and they shatter and electrons are not going to be able to flow through them however okay ionic solids should not conduct electricity however the cool thing is if you put in water okay so if you have ions dissolved in water the ions you'll have the ability to move around okay so when we get to chapter six we're going to talk about electrolytes and you may have um had a water that's called electrolyte water right there's even um brands that sell it hold on a sec it's kind of loud in the house [Music] okay so um electrolyte water right let me write this up here elec lights some of you may have been familiar with electrolytes so electrolytes are aqueous solutions that have electrons ions dissolved in water okay you can have salt water and you can have like you might buy water that's alkaline water okay that's got some magnesium or potassium carbonate dissolved in it or bicarbonate and these ions can move around because now the water is surrounding the ions so we'll get into solution theory in chapter six which is all about the composition of substances and solutions and we'll talk more about it then so lewis theory is going to predict that a liquid ionic compound so if i could take my sodium chloride and melt it or i could take my sodium chloride and put it in water they should conduct electricity and has been shown that that is the case ionic compounds will conduct electricity in the liquid state or when dissolved in water um so here's an interesting thing i don't know if you guys have this slide um it's comes up twice in my lecture notes but i can't find it it's the weirdest thing that's happening within powerpoint i was looking for the slide i wanted to make sure i had it um because last semester it was buried in my notes and now it's not in my notes when i look at them it's only when i have it in presentation mode that it's coming up so i'm trying to find where it is buried behind things can't find it anyway i'm going to sit on this for a second you can take a screenshot of this if you want it's going to come up again so here's a summary ionic compounds are going to be hard and brittle crystalline solids crystalline long-range crystalline order all ionic solids are all ionic compounds are solids at room temperature and one of the things that you want to be able to do after you've had chemistry is to look at a compound look in some pure substance and say hmm is that ionic is that molecular because the physical and chemical properties are very different between them now melting points are generally going to be greater than 300 degrees celsius why is that in order to go from the solid to the liquid you have to break some of the attractive forces between the pluses and the minuses so you have to break some attractive forces you have to put a lot of heat in so heat is a type of energy that you can break attractive forces so if you think of a solid all these perfectly um ordered positives and minuses and then you think of a liquid well you think of there's some motion here these can all these flow around they're kind of touching each other there's more space in liquids than there is in solids okay and solids tend to melt and everything compresses down um and then the liquid state will conduct electricity because now the ions can flow because one of the properties of a liquid is flowing many of these are soluble in water now we're going to get to a very important part of chapter seven about solubility so this is chapter six and chapter seven and those of you who remember from your high school or chem three chem 38 whatever you just tried you know that there are there are compounds that aren't soluble let's talk about one of them just as an example this one right here calcium carbonate calcium carbonate what is calcium carbonate where do we find it give me the common name for calcium carbonate where would we find calcium carbonate where is it see chalk absolutely shells on the beach absolutely so if you think about this so chalk this is something that we use substance right we used to use teaching right um it comes from usually shells on the beach right so you break down these shells shells the crustaceans and the critters the half shells need their shells if calcium carbonate was soluble in water they would all be sea cucumbers they wouldn't have any shells right another very important place that calcium carbonate is found naturally occurring is in our bones our bones are calcium carbonate okay so we do not want our bones dissolving in our blood right so many of these compounds are soluble many of these are not another place you find calcium carbonate is especially if you're living in a place that has what we call hard water and you're going to have water spots you'll have water spots on your faucets and maybe if um you go to your sink you'll notice this white crusty part around where um any of the water has splashed or around your faucet right so calcium carbonate calcium little bits of calcium are naturally occurring in our water which is good we need the calcium we have to drink water that has some calcium and magnesium in it okay you don't want to get rid of that we need that and it also buffers the water so that the water doesn't end up being too acidic or too alkaline okay but this calcium is cruising around and then carbon dioxide from the air comes in and then remember carbon dioxide reacts with water to make carbonic acid and the calcium can see that carbonic acid or even the carbonate because the h's can come off and then it forms a precipitate and that calcium carbonate just a little bit it's called total dissolved solids in water just a little bit comes out and then we can digest it okay because it goes into our stomach where we have acid the calcium and the carbonate have a chemical reaction in there so calcium carbonate very important not soluble in water okay the tiniest bit of it is and even that tiny tiny bit that is like when i say soluble not soluble there's kind of like there's a cut off between basically the amount of ions dissolved in water and what is considered to be soluble or not one of the things you can tell if something soluble or not is you take a little bit of it and you try to dissolve it in water if it doesn't dissolve we consider it not soluble right so the calcium carbonate and typically is not soluble now if i look at sodium chloride you guys probably have it at home you cook with it um it totally dissolves up to a certain point right you can overwhelm the water with too much sodium and chloride and then it stops dissolving at that point but um that's another chapter six concept okay i'm getting ahead of myself don't want to do that um i mentioned this earlier that um solids and liquids okay so this is my solid this my liquid heat this is a form of energy this thermal energy we'll get to this in chapter nine um it will disrupt the attractive forces and now ions can move and electricity can flow and actually have a just a little video i want to show you guys i'm going to show you so this image here is an image that is in i am seeing hold on if you guys are seeing what i'm seeing on my ipad you are not seeing oh there it goes it changed um okay this is the image i'm looking for okay so this is an image in your book and um on the left hand side you have a um a light bulb okay and this light bulb is connected to it has two little uh wires down here okay okay but they aren't touching each other and they are sitting in solid sodium chloride and then there's heat there's a bunsen burner here and there's a blow torch okay you got to put a lot of heat in here and as soon as you have a liquid then the light bulb turns on because electricity can flow but i also have a video that i want to show you guys so give me just one second my computer is working very slowly by the way i'm sorry i am restarted it and it's still not super happy with me so hopefully we can do this there it is okay uh there are no words to this video so i'll just uh describe what's going on and it is working slowly and the quality looks terrible sorry okay so here's what you have you have a light bulb here and you have two electrodes and they are not touching each other and you have a um this is actually connected to a battery okay so the battery's on and if these two electrodes are touching each other then electrons could flow and the light would be illuminated so now what this person is going to do is show you when the two electrodes are touching the light is illuminated okay quality just got better so um a little bit of morton salt okay this is just sodium chloride that is solid is going to be poured into a crucible that's what this little glass thing is called it's called a crucible and you can see the close-up picture here that it is a solid it's crystalline and now they're gonna use a blowtorch so it just has to get up to um uh several hundred degrees celsius i don't remember what the melting point of sodium chloride is but it's pretty hot more than 300 okay and as soon as a liquid is formed take a look at that not cool as soon as the liquid okay so as soon as i went from solid to liquid ions could flow and if you notice these electrodes still are not touching each other and you can see how hot this solution is um actually it's not a solution it's a pure liquid sodium chloride you can see how hot the pure liquid sodium chloride is and because the electrodes are starting to glow they're showing black body radiation okay all right so cool and the model that it was came up with is a very good model