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AP®︎/College Biology
Course: AP®︎/College Biology > Unit 1
Lesson 3: Introduction to biological macromoleculesCovalent bonds
AP.Chem:
SAP‑3 (EU)
, SAP‑3.A (LO)
, SAP‑3.A.2 (EK)
, SAP‑3.A.3 (EK)
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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can someone tell me what a diatomic element is? whoever does thanks for doing so(18 votes)
Diatomic means a molecule of 2 atoms bonded together
Most commonly you’ll see it with H, N, O, F, Cl, Br and I which naturally all exist as diatomic molecules: H2, N2, O2, F2, Cl2, Br2 and I2(50 votes)
how do you know if the bond is ionic or covalent?(9 votes)- Look at the difference in electronegativity between the two atoms, if it’s more than about 1.7 then it’s more on the ionic side of things.(30 votes)
Why doesn't the oxygen take an electron from the hydrogen because it is more electronegitive?(9 votes)
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)
Can someone please explain what the octet rule is?(5 votes)- Atoms tend to react until they have 8 electrons in their outermost shell. 8 = oct.(13 votes)
how do i determine when there is a covalent bond and when there is an ionic one?(3 votes)- a covalent bond is a bond between 2 non metals while an ionic bond is between a metal and a non metal(10 votes)
Please tell me the difference between single,double and triple covalent bonding(5 votes)- A single bond has 1 bond between the atoms
A double bond has 2 bonds between the atoms
A triple bond has 3 bonds between the atoms(5 votes)
- 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)
- Phosphorus doesn’t need to follow the octet rule(6 votes)
At5:26, 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'.(2 votes)- A lower case delta is used for partial charges, see: https://en.m.wikipedia.org/wiki/Partial_charge
Heat uses an upper case delta(6 votes)
(WRT H2O molecule) Shouldn't the partial charge gained by O be twice that of the magnitude of partial +ve charge on each Hydrogen atom as H2O is 'electrically' neutral?(3 votes)- Yes mathematically that should be the case. Physically it also makes sense since the oxygen atom is withdrawing electron density from two hydrogen atoms while each hydrogen atom is only donating electron density to the one oxygen atom.
Often though when we consider the partial charges at the poles water we think of the entire molecule where the two partial positive charges at the hydrogen atoms are merged into a single partial positive charge equal in magnitude to the partial negative charge at the oxygen.
Either way you think of it, it'll still make the molecule electrically neutral as you stated.
Hope that helps.(3 votes)
Aside from the oxygen example, how would covalent bonding work with other elements?(1 vote)- 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)
5:26Video 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.