Covalent Bonds - Video Tutorials & Practice Problems
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1
concept
Covalent Bonds
Video duration:
4m
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Video transcript
In this video we're going to begin our lesson on covalent bonds. And so covalent bonds are really just defined as an interaction between 2 atoms that results from the sharing of electrons. And so really in this context here you can think that the word covalent just means sharing of electrons. And so if electrons are being shared between 2 different atoms then we have ourselves a covalent bond. Now the thing is that electrons that are being shared between atoms can be shared in 2 different ways. And this leads to 2 different types of covalent bonds that share the electrons in different ways. The first type of covalent bond that you all should know is the non polar covalent bond, and then the second type of covalent bond that you all should know is the polar covalent bond. Now later in our course in a different video we'll talk more about the differences between non polar covalent bonds and polar covalent bonds, But for now what I want you guys to know is that the reason that there are 2 different types of covalent bonds is because the 2 types of covalent bonds, exist due to differences in atoms' electronegativities. And so electronegativity is really just defined as a measure of an atom's attraction to electrons, or in other words it's a measure of how hard atoms pull on electrons, and so electronegativity is really scaled from 0 all the way up to 4 at its maximum. So an electronegativity of 0 means that an atom is not very electronegative at all, and that means that it does not pull hard on electrons. Whereas an electronegativity value that's closer to 4 means that the atom is very electronegative and that it pulls really really really hard on electrons. So that's important to keep in mind about electronegativity. Now when we take a look at a periodic table, what you'll notice is that the atoms are arranged based on their electronegativity values. And so you can see that as we go from the left hand side to the right hand side of the periodic table, there is increasing there are increasing values of electronegativities. So within these tables you can see that underneath we're showing you these numbers and these numbers here, represent the electronegativity values of these atoms. And so you can see that as you start from the left and make your way to the right, atoms become more electronegative. But also, notice that atoms also increase in electronegativity from bottom to top. So if you pick any column, notice if you start at the bottom and make your way to the top, the atoms become more and more electronegative. And so that's important to note that the electronegativity is really what is the reason for these two different types of covalent bonds that we're going to talk more about moving forward. Now, there's no need to have to memorize all of these electronegativity values. That's something that you're likely not gonna need to know. But what you should be able to recognize is that oxygen is one of the most electronegative atoms that exist. In fact, the only atom that is more electronegative than an oxygen atom is Fluorine. And so this is important to keep in mind especially when we start to talk about the water molecule later in our course which we know water molecules have 1 oxygen atom. So that's important to keep in mind. Oxygen is very electro negative and it pulls really really hard on electrons for that reason. So this here concludes our introduction to covalent bonds and again moving forward in our course we'll talk more about non polar and polar covalent bonds. So I'll see you all in our next video.
2
Problem
Problem
When two atoms share a pair of electrons, the bonding is referred to as:
a) Ionic.
b) Covalent.
c) Unstable.
d) Hydrogen.
e) Polar.
A
Ionic.
B
Covalent.
C
Unstable.
D
Hydrogen.
E
Polar.
3
concept
Nonpolar Covalent Bonds
Video duration:
5m
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Video transcript
So from our last lesson video, we already know that there are 2 types of covalent bonds due to the differences in atoms' electronegativities. Or in other words due to the differences in how hard atoms pull on electrons. And so in this video we're going to talk about our first type of covalent bonds which are the non polar covalent bonds. And so of course non polar covalent bonds are a type of Covalent Bond and we already know from our last lesson video that the term Covalent refers to the sharing of electrons between atoms. And so there will be sharing of electrons between atoms in nonpolar covalent bonds. Now, the term non polar is a term that refers to equal and so non polar covalent bonds are described by equal sharing of electrons between atoms. Now, the reason that the electrons are being shared equally in nonpolar covalent bonds is due to the equal or similar electronegativities of the atoms involved in the nonpolar covalent bond. Or in other words, the two atoms involved in a nonpolar covalent bond will pull on electrons equally or very similarly and therefore they share those electrons equally. And so if we take a look at our image down below we'll be able to see 3 different examples of non polar covalent bonds. And so once again non polar covalent bonds are described by equal sharing of electrons between atoms. And so we have this little interesting image here of 2 people that seem very friendly and they are sharing this electron between them very very equally. And so notice each of these people here represents an atom. So we've got 2 atoms here and they are sharing this electron between them equally. And so notice our first example, what we have is a molecule called hydrogen gas whose chemical formula is h two meaning that it consists of 2 hydrogen atoms, one right here and the other one right here. And notice that there is a line between these 2 hydrogen atoms. That line represents a covalent bond. In this case, it represents a non polar covalent bond. Now the reason that it is a non polar covalent bond is because these 2 identical hydrogen atoms have equal electronegativities which means that they pull equally on this shared pair of electrons between them. And so those electrons will be shared equally between the 2 atoms. And again equal sharing of electrons between atoms results in non polar covalent bonds. And so down below we have another representation of the same exact hydrogen gas molecule and once again what you'll notice is that, there is a pair of electrons that is being shared between these 2 hydrogen atoms and those electrons are being shared equally, resulting in this non polar covalent bond. Now the next example that we have also is going to consist of 2 identical atoms sharing electrons And this is a molecule called oxygen gas whose chemical formula is o 2, so it's 2 identical oxygen atoms sharing, in this case, 2 pairs of electrons, in a double bond that's why you see two lines between those 2 oxygen atoms and, these 2 covalent bonds are non polar covalent bonds because those 2, pairs of electrons are being shared equally between those 2 identical atoms. And that's because these 2 identical oxygen atoms have equal electronegativities and they pull equally on those 2 shared pairs of electrons. And so notice in this image down below, you'll see there is one pair of shared electrons there and another pair of shared electrons here and they are being shared equally between, the oxygen atom on the left and the oxygen atom on the right. Now in our last example, unlike the first two examples where the atoms were identical, In this example, notice that there are different types of atoms or different elements. So we have a carbon atom and 4 hydrogen atoms and so this is the molecule methane. And so what you'll notice is that the carbon atom is going to be central and the 4 hydrogen atoms will be around the carbon atom, and each of those hydrogen atoms is bonded to the central carbon atom via non polar covalent bonds. So there are 4 non polar covalent bonds linking each of the 4 hydrogen atoms to the carbon. And so the reason that these are non polar covalent bonds here is once again because the Carbon and Hydrogen atoms have very similar electronegativities. They are not identical but they are similar and close enough to the point where those electrons are going to be shared relatively equally creating a non polar covalent bond. And so that's exactly what we see down below, a pair of electrons being shared, with each of the hydrogen atoms and the carbon atom. And so, over here what we have is this, another image showing you 2 people in a tug of war match and notice that the electron symbol which is an e with a little negative as the exponent is right in the middle and so each of these people here represents an atom. This represents 1 atom and over here this other person represents a second atom. And, the electron, notice is right in the middle, perfectly evenly here in the middle which shows that these two people are pulling equally on the electron. And so there is going to be equal sharing of electrons in nonpolar covalent bonds and that is the key takeaway here. And so this concludes our brief introduction to non polar covalent bonds and we'll be able to get some practice as we move forward and then we'll discuss polar covalent bonds. So I'll see you all in our next video.
4
Problem
Problem
What makes a covalent bond nonpolar?
a) The bonded atoms share electrons unequally.
b) The bonded atoms share electrons equally.
c) The bonded atoms have equal electronegativities.
d) The bonded atoms have unequal electronegativities.
e) a and d only.
f) b and c only.
A
The bonded atoms share electrons unequally.
B
The bonded atoms share electrons equally.
C
The bonded atoms have equal electronegativities.
D
The bonded atoms have unequal electronegativities.
E
a and d only.
F
b and c only.
5
concept
Polar Covalent Bonds
Video duration:
6m
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Video transcript
So now that we've introduced our first type of covalent bond, the non polar covalent bonds in our previous lesson videos, in this video we're going to introduce our second type of covalent bond, the polar covalent bonds. And so recall from our previous lesson videos that the term covalent refers to the sharing of electrons between atoms and so these polar covalent bonds are going to involve the sharing of electrons. Now the term polar specifically refers to unequal and so polar covalent bonds are characterized by unequal sharing of electrons between atoms. Now, the reason that there is unequal sharing of electrons between atoms in these polar covalent bonds is due to different electronegativities of the atoms in a polar covalent bond or in other words, the 2 atoms involved in a polar covalent bond will pull on electrons with different strengths, leading to unequal sharing of those shared electrons. Now, of course, unequal sharing of these negatively charged electrons is going to lead to an unequal distribution of those negatively charged electrons between these atoms and that will lead to partial charges throughout the molecule. Now this symbol that you see right here is the Greek symbol delta which represents partial, and so these are not full charges that we're talking about, these are fractioned or partial charges. And so, you'll see this symbol delta throughout our image down below and you'll also see it in our images moving forward as well. And, so if we take a look at our image down below we'll be able to see 3 different examples of polar covalent bonds. And so our first example is within this molecule called hydrogen chloride whose chemical formula is HCl. One hydrogen atom and one chloride atom. And of course the line between these two atoms represents a covalent bond, a shared pair of electrons and this is specifically a polar covalent bond and that is because this chloride atom has a much higher electronegativity in comparison to the hydrogen atom which means that the Chloride atom pulls on electrons harder and so the shared electrons in this, polar covalent bond will be pulled more towards the chloride atom and, less towards the hydrogen atom. And recall that these electrons are negatively charged and so there will be a partial negative charge on the chloride atom and so we can fill that in here, partial negative charge. And, on the hydrogen atom because electrons are being pulled away from it, negatively charged electrons are being pulled away from it, giving up a negative charge will make you more positive and so it will have a partial positive charge. And that's exactly what we see down below. Notice that this shared pair of electrons right here is being shared unequally in this polar covalent bond and so the chloride atom has the partial negative charge because it pulls harder on these electrons and the hydrogen atom is gonna have a partial positive charge because it pulls less less hard or more weakly on those electrons, and so it does not have those negatively charged electrons as much and gains a partial positive charge. And so you can see how the unequal distribution of these electrons leads to these partial charges. Now in the next example, what we have is water whose chemical formula is of course H2O. We know it has 2 Hydrogen atoms and one oxygen atom and, these lines between the oxygen and the hydrogen represent polar covalent bonds and that is because recall that oxygen is one of the most electronegative atoms that exist and so it pulls on electrons very very hard whereas the hydrogen atoms do not pull very hard on electrons. So these electrons that are being shared are gonna be shared unequally leading to these polar covalent bonds. And so, notice that the oxygen atom that pulls harder on electrons is gonna have the negatively charged electrons for more time so it gains a partial negative charge. And each of the hydrogen atoms is, gonna have the electrons for less time and so they gain a partial positive charge. And so every single water molecule is going to have a partial negative charge on the oxygen and partial positive charges on the hydrogen And so that's something important to keep in mind about water. Now in our last example over here what we have is ammonia whose chemical formula is NH 3. So there's 1 nitrogen atom and 3 hydrogen atoms. And again, each of these lines represents a polar covalent bond because nitrogen is much more electronegative than the hydrogen. And so, it pulls on the electrons harder. And so the electrons are going to be pulled towards the nitrogen atom. So it is going to gain a partial negative charge as indicated in our image, and each of the hydrogen atoms is going to have a partial positive charge. And so once again, the main takeaway here is that polar covalent bonds are characterized by unequal sharing of electrons between atoms and, it can lead to these partial charges. Now, if we look at our image on the right hand side over here, notice we have this analogy with 2 people playing the tug of war game pulling on this rope. Now, notice each of these people represents an atom. So we have 1 atom over here and another atom over here. And right in the middle, what we have is the electron. The e with the negative symbol is the electron. And notice that this atom over here is pulling harder on the electrons and so the electron is going to be closer to this atom on the right than it is to the one on the left. And because this electron is negatively charged it gives this atom on the right a partial negative charge whereas the atom on the left is gonna have a partial positive charge since it has the electrons, for less time. And so this is an analogy showing you unequal sharing of electrons, So this is hopefully helpful to help you better understand these polar covalent bonds. And so we'll be able to get some practice applying these concepts moving forward, so I'll see you all in our next video.
6
Problem
Problem
If a covalent bond is polar:
a) Electrons are not shared by atoms.
b) Protons are shared by atoms.
c) The bond is not important to living cells.
d) One of the atoms has a partial negative charge.
e) The bond is not a strong bond.
A
Electrons are not shared by atoms.
B
Protons are shared by atoms.
C
The bond is not important to living cells.
D
One of the atoms has a partial negative charge.
E
The bond is not a strong bond.
7
Problem
Problem
Bonds between two atoms that are equally or similarly electronegative are ________.
A
Polar covalent bonds
B
Nonpolar covalent bonds
C
Intermolecular bonds
D
None of the above
8
Problem
Problem
The hydrogens and oxygen of a water molecule are held together by ______ bonds.