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Current time:0:00Total duration:6:57

Video transcript

this video we're going to look at how to draw dot structures of simple organic molecules that have single bonds so if I look at the molecular formula ch4 which is methane and I want to draw a dot structure for the methane molecule I would go over here to my organic periodic table and find carbon and I can see carbon is in Group four therefore carbon will have four valence electrons so I can draw a carbon with its four valence electrons around it like that remember from general chemistry valence electrons are the electrons in the outermost energy level so carbon has four valence electrons in its outermost energy level next I have to think about hydrogen and hydrogen is in Group one on the periodic table therefore hydrogen will have one valence electron and so I can go ahead and put a hydrogen in there with one valence electron and I know I do that three more times so I keep putting in hydrogen's each with one valence electron so a total of four hydrogen's and now I can start connecting my dots I know that two valence electrons equals one single covalent bond so there is a single covalent bond there's a single covalent bond and then I have two more here so this is my complete dot structure for methane now I can see that carbon is surrounded by eight electrons here so we can go ahead and highlight those so if I'm counting the electrons around carbon and we two four six and eight like that and eight electrons around carbon makes carbon very stable and if we look at the periodic table we can see why so if I look at the second period I can see that the valence electrons for carbon would be one two three and four and to get to eight electrons we would go five six seven eight so if carbon is surrounded by eight electrons that let it's like it has the electron configuration of a noble gas which makes it very stable because all the orbitals in that energy level are now full so an octet of electrons is the maximum number of electrons for carbon if we look at hydrogen we can see that each hydrogen is surrounded by two electrons and so if I find hydrogen here hydrogen is in the first energy level and so here's one electron and here's two electrons so in the first energy level there's only an s-orbital and so and that s orbital holds a maximum of two electrons and we get to the electron configuration of a noble gas and so hydrogen is is stable with having only two electrons around it let's look at another dot structure and let's do one that has nitrogen in it so if I look at the molecular formula ch3 NH two I'm going to once again start with carbon in the center with its four valence electrons around it like that and I know that there are three hydrogen's on that carbon so I can go ahead and put those three hydrogen's each hydrogen has one valence electron like that and then on the right side I'm going to think about nitrogen so I need to find nitrogen on my periodic table nitrogen is in group 5 therefore nitrogen has 5 valence electrons I can represent those valence electrons as 1 2 3 4 & 5 like that and I still have I still have two hydrogen's to worry about right so I still have these two hydrogen's here and I can see there's a place for them on the nitrogen so I can go ahead and put a hydrogen in here and a hydrogen in here and connect the dots and I have my dot structure and I can also check on my octet rule so carbon has an octet and nitrogen has an octet as well so let's go ahead and verify that so there's two electrons here four six and eight so nitrogen is in the second period and so nitrogen is also going to follow the octet rule when you're drawing your dot structures let's do let's do one with oxygen next so if I wanted to draw the dot structure for methanol methanol is ch3oh and so once again I start with carbon with the four valence electrons and I have three hydrogen's each one with one valence electron like that and so I can go ahead and put in those three hydrogen's next I have oxygen so I need to find oxygen on my organic periodic table and I can see that oxygen is in group six right here so oxygen is going to have six valence electrons around it so I can go ahead and draw in oxygen and I can put its six valence electrons in one two three four five and six like that and then I'm going to put in the hydrogen right so now I have a hydrogen to worry about and I know that hydrogen has one valence electrons so I can see there's a place for it over here and once again I can connect the dots and see all of the single covalent bonds in this molecule so that's one bond that's another bond and then I can see the carbon is bonded to the oxygen and the oxygen is bonded to this hydrogen as well again we can check our octet rule so the carbon has eight electrons around it and so does the oxygen so heat this would be two right here and then four and then six and then eight so oxygen is going to follow the octet rule now when you're drawing dot structures you don't always have to do this stuff where you're we're drawing each individual atom and summing all of your all of your valence electrons that way you can need to start drawing it so for an example if I gave you c2h6 which is ethane another way to do it we just would just be starting to draw some bonds here and so I have two carbons and is a pretty good bet those two carbons are going to be connected to each other and then I have six hydrogen's and if I look at what's possible around those carbons I could put those six hydrogen's around those two carbon atoms like that and if I do that I'll have an octet around each carbon atom so this would be my dot structure for ethane to double check yourself you could make sure that your dot structure has the correct number of valence electrons so if I'm thinking about each carbon each carbon having four valence electrons and I have two of them I'm going to get eight valence electrons from those two carbons that I have to represent in my dot structure each hydrogen has one valence electron and I have six of them so I need to worry about six valence electrons from the hydrogen so for a total of fourteen so when I look at my dot structure I can check to make sure I have the correct number of valence electrons I need 14 so let's go ahead and count them so this would be two here for six six eight ten twelve and fourteen so I have the correct number of valence electrons represented in my dot structure I also have an octet of electrons around my carbons and so this would be the dot structure for ethane