[Music] okay so the tool we're going to use for making structural predictions or for understanding small molecules is Lewis dot structures that's the tool we're going to use and so in order to appreciate this let's first of all remember that the outer electrons that is those that are available for bonding are called valence electrons right so the valence electrons are the outer electrons and the number of valence electrons is indicated by the group number do you remember what the group number is look over here to periodic table the group number this is Group one over here with hydrogen lithium sodium potassium Group one group two is beryllium Group three is boron aluminum dad gallium right carbon silicon germanium is group 4 group 5 is here now there's a couple naming conventions for the periodic table right so this is called Group one or group 1a or improved 11a right I think that's a misprint it's definitely a misprint okay but this is group 2a or Roman numeral 2a or 2a all right I'm just gonna call it Group one and this something to call group two I'm gonna call this group three you can see that sort of fits with these other two naming conventions the lower two all right and group four and five and so on it's not really important what what naming convention we use of course or else they wouldn't be three but anyway it's just a proof disappointed out Group one has one valence electron group two has two valence electrons Group three has three valence electrons group 4 and so on does that make sense alright so again the the number of valence electrons is indicated by that group number all right now and finally bonds are formed by the sharing of valence electrons we call those valence electrons when they're shared we call them covalent electrons right that's what a covalent bond is okay so let's look at a question that we might get from a section like this draw the Lewis structure of a boron atom okay so for a boron atom to come here in blue I'm gonna say Lewis structure we're gonna indicate the core of the Orang atom that is not the valence electrons but all the inner electrons and the nucleus we're gonna indicate just with the chemical symbol beat alright so then we're gonna indicate the valence electrons by coming over here all runs in Group three can you see it right there okay and so I'm gonna say one two three that is the Lewis structure of a boron atom by the way it's just as accurate to say one two three it's just as accurate to say one two three right so typically I'm gonna start in I guess on the west side of this boron atom and sort of go around but I don't know why I went to the top doesn't matter right this is the Lewis structure of a boron atom I'm not indicating anything in particular by putting where I put those electrons oftentimes it will pair them okay so let's now do the Lewis structure of a nitrogen atom so again first of all I'm gonna draw the core by I'm going to indicate the quota chemical symbol that's both the nucleus and all the inner electrons now we draw the left the the valence electrons with Lewis structures let's go over and see where nitrogen is and boom there it is in group five right there seen you seen it nitrogen root five since it's in group five it has five valence electrons let me go one two three four five okay and that is the Lewis structure of a nitrogen atom okay again we might have drawn it one two three four five this is equally correct okay and generally especially for the smaller ends we're gonna draw them only on the left and right and top and bottom right so we're gonna we're gonna pair them right so those are the Lewis structures of atoms now let's consider the Lewis structure of a I guess I was putting that in there first let's consider the lewis structure of a molecule this molecule is formaldehyde okay and so let's do what we did before remember now from previous lecture that carbon has a tendency to have four bonds oxygen has a tendency to have three bonds I'm sorry two bonds and hydrogen has a tendency to have one bond right so let's first of all draw these guys they're going to be central because they have more bonds right and now let's draw the hydrogen's well I could draw a hydrogen here and a hydrogen here which I'm going to do because carbon Scott wants to have four bonds right and oxygen wants to have two bonds right okay all right so let's draw the lewis structure of C h2o which is formaldehyde first thing we're gonna do is we're gonna draw all the atoms and we're going to default we're gonna assume that they're symmetric let me get that back in blue let's assume symmetry here okay right and now I'm gonna draw the valence electrons hydrogen is in Group one let me draw electron there I'm gonna draw an electron here I'm assuming it's gonna share something or if it was carbon right in oxygen I'm gonna say one two three four five six okay and carbon is in Group four so it's one two three four okay now we're going to assume these guys are bonded because that's what a molecule has right covalent bond so I'm gonna say I'm gonna redraw these two electrons in red I'm going to draw these two and I'm gonna draw them as a covalent bond I'm gonna draw these two as a covalent bond when I draw these two as a covalent bond now remember from a previous conversation the carbon has a tendency to have four bonds and oxygen has a tendency to have two bonds right so look at this if I take this electron in that electron and I'm gonna erase it and redraw it here right then sure enough I've got I've got carbon with my four bonds and oxygen with my two bonds it looks like oxygens got two lone pairs of electrons also okay so the last thing I'm gonna do in order to appreciate it that's a good a good structure or not is I'm going to subject it to the octet rule which I said nothing about so far but the octet rule is something we learned in a previous class the active rule might go with gray okay so for the octet rule I'm gonna circle each atom and count every electron that's inside that circle right these electrons are covalent right they belong both to the carbon into the hydrogen so looks like there's two electrons here since hydrogen's in the first period only has a capacity for two electrons so that's fine it's like that's in the same shape right two electrons and that's fine here are all the electrons that are in the valence shell of carbon two four six eight that's fine and here are the valence electrons that are in I'm sorry yeah the valence electrons for the oxygen again remember these four electrons are covalent right two four six and eight okay and so it looks like that satisfies the octet rule in fact that is the Lewis structure of formaldehyde sometimes what I'm gonna do when I'm done is I'm gonna redraw everything make it a little bit prettier right especially if I didn't give my chair when I was doing my my notes to do its shape might be confusing me and it got so much there and sure enough this is the Lewis dot structure of formaldehyde okay hope that's helpful