Dot structures
dot structures I: single bonds
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- In this video, we're going to look at how to draw a dot structure,
- which has a simple organic molecule,
- which has single bonds.
- So, if I look at the molecular formula,
- CH4, which is methane.
- I want to draw a dot structure for the methane molecule.
- I will go over here to my organic periodic table,
- and find carbon,
- and I can see carbon is in Group 4.
- 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
- on the outer-most energy level.
- So, carbon has four valence electrons
- in its outer-most energy level.
- Next, I have to think about hydrogen,
- and hydrogen is in Group 1 on the Periodic Table.
- Therefore, hydrogen will have one valence electron.
- So, I can go ahead and put the hydrogen in there
- with one valence electron.
- I know I have to do that three more times.
- So, I keep putting the hydrogens
- each with one valence electron.
- So, the total of four hydrogens.
- And now, I can start connecting my dots.
- I know that two valence electrons equal to one single covalent bond.
- So, there is a single covalent bond.
- There is a single covalent bond.
- And then, I have two more here.
- So, this is my complete dot structure for methane.
- Now, I can see the carbon is surrounded by
- eight electrons here.
- So, we can go ahead and highlight those.
- So, if I count on the electrons around the carbons,
- it would be two, four,
- six and eight like that.
- And eight electrons around the 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 electron of the carbon
- would be one,
- two,
- three and four,
- and to get eight electrons,
- we will go to five, six, seven, eight.
- so, if carbon is surrounded by eight electrons,
- it's likely to have the electron configuration of noble gas,
- which makes it very stable, because all the orbitals in the energy level on are full.
- so, octetable electrons is the maximum number of electrons for the carbon.
- if we look at the hydrogen, we can see each hydrogen is surrounded by two electrons.
- so if i find the hydrogen here, the hydrogen is in the first energy level,
- so here is one electron, and here is two electrons
- so on the first energy level, there is only an s-orbital, and so
- that orbital holds maximum two electrons and we get to the electron
- configuration of the noble gas,
- and so hydrogen is stable with having only two electrons around it.
- let's look at another dot structure,
- and let's do one tha has a nitrogen in it.
- so if i look at the molecular formula, CH3-NH2,
- i'm going to once again start with the carbon in the center,
- with its four valence electrons around it like that.
- and i know that three hydrogens on the carbon
- so i can go ahead and put three hydrogens
- each hydrogen has one valence electron, like that.
- and on the right side, i'm going to think about the nitrogen.
- i need to find the nitrogen in my periodic table.
- nitrogen is in Group 5.
- Therefore, nitrogen has five valence electrons.
- so i can represent the electron as one, two, three, four and five, like that.
- and i still have two hydrogens to worry about, right?
- so i still have two hydrogens here.
- and i can see the 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 my octet rule,
- so carbon has an octet,
- and nitrogen has an actet as well,
- so let's go ahead and verify that.
- so there is two electrons here,
- four, six, and eight.
- so nitrogen is in the second period,
- so nitrogen is also going to follow the octet rule, when you draw dot structures.
- let's do one more.
- oxygen, next.
- so if i want to draw a dot structure, for methanol,
- methanol is CH3OH.
- so once again, i'll start carbon, with four valence electrons,
- and i have three hydrogens, each one with one valence electron like that
- so i can go ahead and put those three hydrogens
- next i have oxygen
- so i need to find the oxygen in my organic periodic table
- and i can see that oxygen is in group 6 right here
- so oxygen has 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 i know now i have a hydrogen to worry about
- and i know hydrogen has one valence electron,
- so i can see there is a place for 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,
- now i can see that carbon is bonded to oxygen,
- and oxygen is bonded to this hydrogen as well
- again we can check our octet rule
- so, the carbon has eight electrons around it
- so is the oxygen
- this will be two right here
- and then four, and then six, and then eight
- so the oxygen is following the octet rule
- now when you are drawing a dot structure,
- you don't always have to do this stuff where you are drawing each individual atom,
- and summing all the valence electron in that way
- you can just start drawing it
- so for example, if i gave you C2H6, which is ethyne
- another way to do it is we just do
- we'd just be started drawing the bonds here
- so i have two carbons,
- and there is a pretty good bet that the two carbons are connected to each other
- and i have six hydrogens
- and if i look at what's possible around those carbons,
- i could put those six hydrogens around those two carbon atoms like that
- and if i do that, i will have octet around each carbon atom
- so this would be my dot structure for ethyne.
- 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 electron of hydrogens
- so the total of 14
- so i'm look at my dot strcuture
- 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 will be two here,
- four, 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
- so this would be the dot structure for ethane
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