Covalent Bonds - Online Tutor, Practice Problems & Exam Prep

Covalent bonds involve the sharing of electrons between atoms, categorized into nonpolar and polar covalent bonds based on electronegativity differences. Nonpolar covalent bonds feature equal sharing of electrons, as seen in molecules like H₂ and O₂, where identical atoms share electrons equally. In contrast, polar covalent bonds exhibit unequal sharing, leading to partial charges, as in HCl and H₂O, where more electronegative atoms attract electrons more strongly. Understanding these concepts is crucial for grasping molecular interactions and properties.

Covalent Bonds

In this video, we're going to begin our lesson on covalent bonds. Covalent bonds are really just defined as an interaction between two atoms that results from the sharing of electrons. In this context, you can think that the word "covalent" just means sharing of electrons. If electrons are being shared between two different atoms, then we have ourselves a covalent bond. Electrons that are shared between atoms can be shared in two different ways, and this leads to two 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 nonpolar covalent bond, and then the second type of covalent bond that you all should know is the polar covalent bond.

Late in our course, in a different video, we'll talk more about the differences between nonpolar covalent bonds and polar covalent bonds, but for now, what I want you guys to know is that the reason there are two different types of covalent bonds is due to differences in atoms' electronegativities. 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. Electronegativity is scaled from 0 all the way up to 4 at its maximum. 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 hard on electrons.

When we take a look at a periodic table, you'll notice that the atoms are arranged based on their electronegativity values. As we go from the left-hand side to the right-hand side of the periodic table, there are increasing electronegativity values. Underneath, we're showing you these numbers which represent the electronegativity values of these atoms. As you start from the left and make your way to the right, atoms become more electronegative. Also, notice that atoms increase in electronegativity from bottom to top. 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. That's important to note that the electronegativity is the reason for these two different types of covalent bonds that we're going to talk more about moving forward. There's no need to have to memorize all of these electronegativity values.

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. 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 one oxygen atom. Oxygen is very electronegative, and it pulls really hard on electrons for that reason. This here concludes our introduction to covalent bonds, and again, moving forward in our course, we'll talk more about nonpolar and polar covalent bonds.

So, I'll see you all in our next video.

When two atoms share a pair of electrons, the bonding is referred to as:

• A. Ionic.
• B. Covalent.
• C. Unstable.
• D. Hydrogen.
• E. Polar.

Nonpolar Covalent Bonds

Now from our last lesson video, we know that there are 2 types of covalent bonds that exist due to differences in atoms' electronegativities or how hard atoms pull on electrons. And so in this video, we're going to talk about the first type of covalent bond, which is the nonpolar covalent bond. Now as we mentioned in our last lesson video, the word covalent here means sharing of electrons, and so even in nonpolar covalent bonds, there's going to be some sharing of electrons. Now the word nonpolar here is really referring to the equal sharing of electrons between atoms, and so nonpolar 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 because the 2 atoms have similar electronegativities or they pull very similarly on the electrons.

And so if we take a look at our example image down below of nonpolar covalent bonds, what you'll see is we've got a little image here of 2 people sharing the electrons very equally. And so you can imagine that hydrogen gas, which is, molecular formula is H₂, is going to be 2 hydrogen atoms as we see right here that are forming a covalent bond and they are sharing electrons, and you can see that down below as well that, these 2 electrons right here are being shared between these 2 hydrogen atoms. Now the hydrogen atoms have identical electronegativities because they are the same atom and that means that the 2 hydrogen atoms pull exactly the same on these 2 electrons that are being shared. And so because they both pull exactly the same on those 2 electrons, they're going to share these 2 electrons really equally. And so that means that this bond that forms between these 2 hydrogens is going to be a nonpolar covalent bond, equal sharing of electrons between these atoms.

Now, very similarly, over here in the middle what we have is oxygen gas which we know its chemical formula is O₂. And so it's going to be 2 oxygen atoms, that are forming bonds between each other. And each of these lines represents the sharing of a pair of electrons and so when we take a look down below right here, notice that there are 2 pairs of electrons being shared which is why it forms this double bond right here. Whereas over here there's only 1 pair of electrons being shared so that's why it only forms a single bond, one bond. Now, the 2 oxygen atoms because they are the same element they have the exact same electronegativity which means that the 2 oxygens are pulling on those shared electrons exactly the same.

And so once again, these two pairs of electrons that are being shared between these two atoms are going to be shared equally, between the two atoms, and that's why these bonds here forming between the 2 oxygens, are going to be nonpolar covalent bonds, equal sharing of electrons between these atoms. Now, so far what we've looked at are, bonds between atoms that are identical, But nonpolar bonds can also form between bond between atoms that are not identical, for example, this image over here. So notice that we're showing you a carbon atom forming bonds with 4 hydrogen atoms. Now the thing is is that carbon and hydrogen have very similar electronegativities. They're not identical, but they're very similar, and what this means is that they're going to pull on the electrons very similarly.

And so that means that each of these, bonds that you see here which represents a pair of electrons being shared is going to be shared equally between the carbon atom and each of the hydrogen atoms. And so because once again there is equal sharing of electrons, these are going to be nonpolar covalent bonds. And the molecular formula of this molecule is CH₄, but the common name for it is methane. And so that's another classic example of nonpolar covalent bonds. Now over here on the right what we have is a little image to help remind you that nonpolar covalent bonds is due to equal sharing of electrons.

So this little symbol that you see right here is a symbol that represents electrons and so you can see that we've got 2 people or 2 atoms if you will that are sharing this electron and pulling on the electron almost like a tug of war match. And so because these two people are of the same size, they're going to pull on the electron pretty equally. They're going to pull on it about the same and so the electron is going to remain pretty much right in the middle here and they're going to be sharing the electrons equally and that is exactly what nonpolar covalent bonds, that's how they're characterized. And so now that we've introduced nonpolar covalent bonds we'll be able to get a little bit of practice in our next video and then we'll talk about polar covalent bonds. So I'll see you all in our next video.

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.

Polar Covalent Bonds

So now that we've introduced nonpolar covalent bonds in our previous lesson videos, in this video, we're going to introduce the second type of covalent bond which is the polar covalent bond. Now, once again, the word covalent here means the sharing of electrons, and so even in polar covalent bonds, there's going to be sharing of electrons, but the word polar here is really referring to the unequal sharing of electrons between atoms, and so polar covalent bonds are characterized by unequal sharing of electrons. Now the reason that the electrons are being shared unequally in polar covalent bonds is due to different electronegativities between the atoms. And so, what this means is that they are going to pull on the electrons with different amounts of strength. Now, of course, unequal sharing of electrons between atoms is going to lead to an unequal distribution of these negatively charged electrons, and an unequal distribution of negatively charged electrons is going to lead to partial charges.

And so this symbol right here is the Greek symbol delta, which can be used to symbolize the word partial, and so you'll see this symbol down below throughout our image. So, in our image over here on the left-hand side, we're showing you a few examples of polar covalent bonds, and so the first example that we're showing you is Hydrogen Chloride whose chemical formula is HCl. So you can see the hydrogen atom over here and the chloride atom over here. Now, hydrogen and chloride have very different electronegativities. Chloride pulls really, really hard on electrons.

It has a high electronegativity, but hydrogen does not pull very hard on electrons. It has a low electronegativity, So there is a big difference here in electronegativities between these two atoms. And so, what that means is that this bond that forms between them, which represents the sharing of 2 electrons, a pair of electrons because chlorine pulls harder on these 2 electrons, these 2 electrons are going to spend more time with the chlorine. And remember the electrons are negatively charged, so because these 2 negatively charged electrons spend more time with the chlorine because the chlorine pulls harder on these electrons because it's more electronegative, the chlorine is going to be associated with a partial negative charge because once again it's pulling these negatively charged electrons harder and so they spend more time with the chlorine and that's what gives the chlorine a partial negative charge. And the opposite happens to the hydrogen, the hydrogen does not pull as hard on the electron because it is not as electronegative.

And so it has these electrons, for less amount of time. And so, if you give up something that's negative, you therefore become more positive, so it gets a partial positive charge. And so, you can see how this unequal distribution of electrons, between the atoms, leads to partial charges. Now we can see something very similar if we take a look at a typical water molecule such as H₂O. It has 2 hydrogen atoms and one oxygen atom.

Now once again, oxygen is one of the most electronegative atoms that exist. It is super electronegative which means that it pulls on these electrons super hard. The hydrogen atoms on the other hand once again are not very electronegative, so they do not pull on electrons that hard at all. And so, of course, each of these lines that we see here represent a pair of electrons being shared between the atoms. So you can see down below we have a pair over here and a pair over here being shared.

And so because, once again, oxygen pulls really hard on these electrons that are being shared, those electrons are going to spend more time with the oxygen and because the electrons are negatively charged it gives the oxygen a partial negative charge. And once again, the hydrogens, on the other hand, are going to have partial positive charges, and this occurs on every single water molecule that exists here. Now the last example that we have of polar covalent bonds is ammonia whose chemical formula is NH₃, and once again you can see it has 1 nitrogen atom and 3 hydrogen atoms. The nitrogen atom is going to be much more electronegative than the hydrogen atoms which are not very electronegative. And so this means that the nitrogen atom is going to pull harder on the electrons.

There are different electronegativities once again. And so these electrons that are being shared here and here and here are going to spend more time with the nitrogen atom and that gives the nitrogen atom a partial negative charge. And once again, the hydrogens are going to have partial positive charges. And so, again, the main takeaway here is that polar covalent bonds are due to unequal sharing of electrons, and unequal sharing of electrons means that the distribution of electrons is going to be unequal as well which leads to partial charges. And so, over here on the far right, what we have is another image to help clear up this idea of polar covalent bonds.

So, basically, you can think in polar covalent bond because they are sharing electrons but they're sharing them unequally, there's pretty much a bully here in this tug of war battle on the electrons. And there's going to be one atom that is much more electronegative than another atom that does not pull very hard on electrons. So, the electron that's being shared is going to spend more time with the more electronegative atom and that creates a partial negative charge. And, the atom that is kind of deprived of the negatively charged electron becomes slightly positively charged, partially positively charged. And so, this all results from unequal sharing of this electron and that's why you can see that the electron is closer to the more electronegative atom because it pulls harder on it.

And so this here concludes our introduction to polar covalent bonds, and we'll be able to get some practice moving forward in our course. So, I'll see you all in our next video.

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.

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

The hydrogens and oxygen of a water molecule are held together by ______ bonds.

• A. Electron.
• B. Hydrogen.
• C. Covalent.
• D. Osmotic.
• E. Non-covalent.
• F. None of the above.

Here’s what students ask on this topic:

What is a covalent bond and how does it differ from other types of chemical bonds?

A covalent bond is a type of chemical bond where two atoms share one or more pairs of electrons. This sharing allows each atom to attain the electron configuration of a noble gas, leading to a more stable molecule. Covalent bonds differ from ionic bonds, where electrons are transferred from one atom to another, resulting in the formation of positively and negatively charged ions. In metallic bonds, electrons are shared among a lattice of atoms, creating a 'sea of electrons' that allows for conductivity and malleability. Covalent bonds are typically found in organic compounds and are crucial for the structure and function of biological molecules.

What are the differences between polar and nonpolar covalent bonds?

Polar and nonpolar covalent bonds differ in how electrons are shared between atoms. In nonpolar covalent bonds, electrons are shared equally because the atoms involved have similar electronegativities. Examples include H₂ and O₂. In contrast, polar covalent bonds involve unequal sharing of electrons due to differences in electronegativity between the atoms. This results in partial charges, with the more electronegative atom gaining a partial negative charge and the less electronegative atom gaining a partial positive charge. Examples include H₂O and HCl.

How does electronegativity influence the formation of covalent bonds?

Electronegativity is a measure of an atom's ability to attract and hold onto electrons. It plays a crucial role in the formation of covalent bonds. When two atoms with similar electronegativities bond, they share electrons equally, forming a nonpolar covalent bond. However, when there is a significant difference in electronegativity between the two atoms, the electrons are shared unequally, resulting in a polar covalent bond. The more electronegative atom pulls the shared electrons closer, creating partial charges within the molecule. Understanding electronegativity helps predict the type of bond and the molecule's properties.

What are some examples of molecules with nonpolar covalent bonds?

Nonpolar covalent bonds occur when atoms share electrons equally due to similar electronegativities. Examples of molecules with nonpolar covalent bonds include hydrogen gas (H₂), where two hydrogen atoms share electrons equally, and oxygen gas (O₂), where two oxygen atoms share electrons equally. Another example is methane (CH₄), where carbon and hydrogen atoms have similar electronegativities, leading to equal sharing of electrons. These molecules are typically symmetrical, which helps in the equal distribution of electron density.

Why do polar covalent bonds result in partial charges on atoms?

Polar covalent bonds result in partial charges on atoms due to the unequal sharing of electrons between atoms with different electronegativities. The more electronegative atom attracts the shared electrons more strongly, causing the electrons to spend more time closer to it. This creates a partial negative charge (δ-) on the more electronegative atom and a partial positive charge (δ+) on the less electronegative atom. For example, in a water molecule (H₂O), oxygen is more electronegative than hydrogen, resulting in partial negative and positive charges on oxygen and hydrogen, respectively.