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Covalent bonds

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Covalent bonds involve the sharing of electron pairs between atoms. Electron pairs shared between atoms of equal or very similar electronegativity constitute a nonpolar covalent bond (e.g., H–H or C–H), while electrons shared between atoms of unequal electronegativity constitute a polar covalent bond (e.g., H–O). Created by Sal Khan.

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  • duskpin tree style avatar for user Jade Rodermond
    can someone tell me what a diatomic element is? whoever does thanks for doing so
    (16 votes)
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  • blobby green style avatar for user samanthatanruiyin
    how do you know if the bond is ionic or covalent?
    (9 votes)
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  • piceratops ultimate style avatar for user Aarnav Sharma
    Why doesn't the oxygen take an electron from the hydrogen because it is more electronegitive?
    (9 votes)
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    • leaf red style avatar for user Richard
      That would mean there would be an ionic bond between the oxygen and the hydrogen. While the electronegativity difference between the two elements is large, it isn't large enough to be considered an ionic bond, rather just a polar covalent bond. Hope that helps.
      (12 votes)
  • duskpin ultimate style avatar for user Athena Mage
    Can someone please explain what the octet rule is?
    (5 votes)
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  • starky seedling style avatar for user lsyali
    how do i determine when there is a covalent bond and when there is an ionic one?
    (3 votes)
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  • scuttlebug purple style avatar for user RehmaZia2006
    Please tell me the difference between single,double and triple covalent bonding
    (4 votes)
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  • blobby green style avatar for user Wouter Beheydt
    How does that work in phosphate? Phosphor has 5 electrons on its outer shell but somehow in phosphate it has a double bond to one and a single bond to three more oxygens. Isn't that two bonds too many? Or do I get something wrong?
    (3 votes)
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  • duskpin seed style avatar for user Beth E. Michael
    Aside from the oxygen example, how would covalent bonding work with other elements?
    (1 vote)
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    • leaf red style avatar for user Richard
      Covalent bonding occurs between atoms of elements who are fairly similar in electronegativities. Atoms of elements with very different electronegativities is what happens in ionic bonds. Elements with the greatest difference are metals and non-metals which is why you usually find ionic compounds formed from a metal and a non-metal. Covalent bonds meanwhile usually occur between non-metals. As long as the individual atoms can form an octet of electrons from sharing electrons in a covalent bond, there's always a possibility. So nitrogen for example is a non-metal with 5 valence electrons and needs 3 more for an octet, and can form a variety of covalent bonds. Two nitrogen atoms can bond to form a triple covalent bond which will give each individual atom an additional 3 electrons for an octet. They end of sharing 6 electrons between the two of them since each bond represents the sharing of 2 electrons. This gives you N2, otherwise known as nitrogen gas which forms the majority of the air you breathe. Another example is nitrogen forming three single bonds to three hydrogen atoms where again nitrogen gets those 3 extra electrons it needs for the octet. Side Note hydrogen is different in that it only needs two electrons to be satisfied. This forms NH3, or ammonia. A final example is one you encounter everywhere in organic molecules (molecules containing carbon), namely a single bond between carbon and hydrogen. Each atom contributes a single electron to be shared between the two atoms. The hydrogen has partial ownership of the second electron in the bond and feels satisfied essentially having two electrons. The carbon has 4 valance electrons and so needs to form 3 other single bonds to 3 other hydrogen atoms to be satisfied having partial ownership of 4 additional electrons and essentially having 8 electrons. This creates CH4, or methane, the simplest organic molecule. The main point of covalent bonding is that it allows atoms to reach an octet of electrons by sharing electrons as opposed to stealing electrons as what happens in ionic bonding. Hope this helps.
      (6 votes)
  • hopper cool style avatar for user Medha Sundar Rajan
    Is it possible to tell if two atoms can have a covalent bond or not? For example, is it possible to see if nitrogen and oxygen can have a covalent bond?
    (3 votes)
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    • aqualine ultimate style avatar for user famousguy786
      Their electronegativity difference of the elements can help us theoretically predict the nature of a bond.
      If the electronegativity difference (usually called ΔEN) is less than 0.5, then the bond is nonpolar covalent.
      If the ΔEN is between 0.5 and 1.6, the bond is considered polar covalent.
      If the ΔEN is greater than 2.0, then the bond is ionic.
      Also, experiments can determine whether a compound is made of ionic or covalent bonds, by examining the melting and boiling points, conductivity and structure.
      (2 votes)
  • purple pi pink style avatar for user You-Know-Who
    At , sal talks a little about the greek letter 'delta'. He says it is a convention in chemistry. Isn't it a symbol for heat in certain cases? Then why use it for the symbol of charge, which is 'Q' or 'q'.
    (1 vote)
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Video transcript

- [Instructor] In a previous video, we introduced ourselves to the idea of bonds and the idea of ionic bonds, where one atom essentially is able to take electrons from another atom. But then because one becomes positively charged and the other becomes negatively charged, they get attracted to each other. Now we're going to go to the other end of the bonding spectrum, where instead of stealing electrons from each other, we're going to share them. Let's say we're dealing with two oxygen atoms. So let me draw one oxygen here. A neutral oxygen has eight electrons total, but six of them are in its outer shell. So it has one, two, three, four, five, six valence electrons. And the way that I arrange them is I pair them up last. So you have these two valence electrons that are not paired with another electron. And now let me draw another oxygen, and I'm going do it with a different color, so we can keep track of the electrons. So another oxygen right over there, also has six valence electrons, one, two, three, four, five, six valence electrons. Now this oxygen on the left, in order to become more stable, it would love to somehow gain or maybe share two more electrons. And of course, this oxygen on the right, it's still oxygen. It also would love to gain or share two more valence electrons. So how could it do it? Well, what if the oxygen on the left shared this electron and this electron with the oxygen on the right, and the oxygen on the right shared this electron and this electron with the oxygen on the left? Well, if they did that, you would have something that looks like this. You have your oxygen on the left. You have the oxygen on the right. And the way we show two electrons that are being shared, let's say these two electrons are being shared, is just a line like this. This shows that there are two electrons that are being shared by these two oxygens. And let's say that these two electrons are also being shared. You would do that with a line like this. And then we could draw the remainder of the valence electrons. This oxygen on the left had, outside of the electrons that are being shared, it had four more valence electrons. And then the oxygen on the right had four more valence electrons, one, two, three, four. Now what's interesting here is the shared electrons, these are going to cause these oxygens to stick together. If they don't stick together, these electrons aren't going to be shared. So what we have formed here is known as a covalent bond, covalent bond. And what's interesting is it allows both of these oxygens in some ways to be more stable. From the left oxygen's point of view, it had six valence electrons, but now it's able to share two more. Remember, each of these bonds, each of these lines represent two electrons. So this oxygen could say, hey, I get to have one, two, three, four, six, eight electrons that I'm dealing with, and the same thing is going to be true of this oxygen on the right. Now there are some covalent bonds that are between not-so-equals. So for example, if we're talking about water and if we're talking about how oxygen bonds with hydrogen. So if we have oxygen right over here, once again, I can draw its six valence electrons, one, two, three, four, five, and let me just draw the sixth one right over there. And if I have hydrogen, hydrogen has one valence electron. So let's say that's a hydrogen right over there with one valence electron, maybe another hydrogen right over there with one valence electron. Oxygen and hydrogen form covalent bonds. In fact, that is how water is formed. And so what would that look like? Well, it would look like this. You have oxygen right over here. You have these two pairs of electrons that I keep drawing. And then this electron right over here could be shared with the hydrogen, and that hydrogen's electron could be shared with the oxygen. So that forms a covalent bond with this hydrogen. And then this electron from the oxygen can be shared with the hydrogen, and that electron from the hydrogen can be shared with the oxygen. And so that would form a covalent bond with that other hydrogen. And now here, once again, oxygen can kinda pretend like it has eight valence electrons, two, four, six, eight. And the hydrogens can kind of pretend that it has two valence electrons. But the one difference here is that oxygen is a lot more electronegative than hydrogen. It's to the right of hydrogen. It's in this top-right corner, outside of, other than the noble gases, that really like to hog electrons. So what do you think is going to happen here? Well, the electrons in each of these covalent bonds are going to hang out around the oxygen more often than around the hydrogen. So if the electrons spend more time around the oxygen, you're going to have, in general, more negative charge around the oxygen. And so you're going to have a partial negative charge on the oxygen end of the water molecule, and then you're going to have partial positive charges on the hydrogen ends of the molecules. And in case you're curious, that little symbol I'm using for partial, that's the lowercase Greek letter delta, which is just the convention in chemistry. And so this type of covalent bond, because there is some polarity, one side has more charge than the other, this is known as a polar covalent bond, polar covalent bond.