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 atoms have similar electronegativities. In contrast, polar covalent bonds exhibit unequal sharing, leading to partial charges, as in HCl and H₂O, where one atom pulls 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 defined as an interaction between two atoms that results from the sharing of electrons. In this context, the word "covalent" means the sharing of electrons. If electrons are being shared between two different atoms, then we have ourselves a covalent bond. Electrons can be shared in two different ways, leading to two different types of covalent bonds that share the electrons differently. The first type of covalent bond that you all should know is the nonpolar covalent bond, and the second type is the polar covalent bond. Later in our course, in a different video, we'll talk more about the differences between nonpolar and polar covalent bonds. For now, what I want you to know is that the reason there are two different types of covalent bonds is due to differences in atoms' electronegativities.

Electronegativity is 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, meaning not very electronegative, to 4, indicating very strong electronegativity. When you look at a periodic table, you'll notice that atoms are arranged based on their electronegativity values. As we move from the left-hand side to the right-hand side of the periodic table, there are increasing values of electronegativity. Also, notice that atoms increase in electronegativity from bottom to top within any given column.

It's important to note that you don't need to memorize all these electronegativity values. However, you should be able to recognize that oxygen is one of the most electronegative atoms, surpassed only by fluorine. This is especially important when we start to discuss the water molecule later in our course, which contains one oxygen atom. Oxygen pulls very hard on electrons due to its high electronegativity.

This concludes our introduction to covalent bonds. Moving forward, we'll discuss more about nonpolar and polar covalent bonds. 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.

• 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. 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. The reason that the electrons are being shared equally in nonpolar covalent bonds is that the two atoms have similar electronegativities or they pull very similarly on the electrons. If we take a look at our example image below of nonpolar covalent bonds, what you'll see is we've got an image here of 2 people sharing the electrons very equally. And so you can imagine, that hydrogen gas, whose molecular formula is H₂, consists of 2 hydrogen atoms, as we see right here, that are forming a covalent bond, and they are sharing electrons, which is also shown below as these 2 electrons right here 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. 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.

Very similarly over here in the middle, what we have is oxygen gas, whose chemical formula is O₂. It consists of 2 oxygen atoms, that are forming bonds between each other. Each of these lines represents the sharing of a pair of electrons and when we look 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. Now, the oxygen atoms, because they are the same element, they have the exact same electronegativity, which means that the 2 oxygens pull 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.

Nonpolar bonds can also form between atoms that are not identical, for example, in the image over here. Notice that we're showing a carbon atom forming bonds with 4 hydrogen atoms. 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. Because there is equal sharing of electrons, these are going to be nonpolar covalent bonds. 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.

Over here on the right, what we have is a little image to help remind you that nonpolar covalent bonds are due to equal sharing of electrons. This little symbol that you see right here 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 it almost like a tug-of-war match. 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 how nonpolar covalent bonds are 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.

• 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 non-polar 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 the 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. 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. In our image over here on the left-hand side, we're showing you a few examples of polar covalent bonds. The first example that we're showing you is Hydrogen Chloride whose chemical formula is HCl. 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 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 the 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 gonna be associated with 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, and 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 1 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 represents 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 on it. And once again, the hydrogens, on the other hand, are gonna have partial positive charges, and this occurs on every single water molecule that exists here.

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's 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 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. There's gonna 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.

• 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 electrons to achieve a stable electron configuration. This sharing can be equal (nonpolar covalent bond) or unequal (polar covalent bond) based on the atoms' electronegativities. Covalent bonds differ from ionic bonds, where electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other. They also differ from metallic bonds, where electrons are delocalized and shared among a lattice of metal atoms. Understanding these differences is crucial for grasping molecular interactions and properties.

What are the main differences between polar and nonpolar covalent bonds?

Polar covalent bonds involve the unequal sharing of electrons between atoms with different electronegativities, leading to partial charges on the atoms. For example, in H₂O, oxygen pulls electrons more strongly than hydrogen, resulting in a partial negative charge on oxygen and partial positive charges on hydrogen. Nonpolar covalent bonds, on the other hand, feature equal sharing of electrons between atoms with similar electronegativities, as seen in H₂ and O₂. This equal sharing means there are no partial charges in nonpolar covalent bonds.

How does electronegativity influence the formation of covalent bonds?

Electronegativity is a measure of an atom's ability to attract and hold onto electrons. In covalent bonds, the difference in electronegativity between the bonded atoms determines whether the bond will be polar or nonpolar. If the electronegativities are similar, the electrons are shared equally, resulting in a nonpolar covalent bond. If there is a significant difference in electronegativities, the electrons are shared unequally, leading to a polar covalent bond with partial charges on the atoms. Understanding electronegativity is essential for predicting molecular behavior and properties.

Can you provide examples of molecules with nonpolar and polar covalent bonds?

Examples of molecules with nonpolar covalent bonds include H₂ (hydrogen gas) and O₂ (oxygen gas), where the atoms involved have identical or very similar electronegativities, leading to equal sharing of electrons. Examples of molecules with polar covalent bonds include H₂O (water) and HCl (hydrogen chloride). In these molecules, the atoms have different electronegativities, resulting in unequal sharing of electrons and partial charges on the atoms. These examples illustrate how electronegativity differences influence bond polarity.

Why is understanding covalent bonds important in microbiology?

Understanding covalent bonds is crucial in microbiology because these bonds form the backbone of biological molecules such as DNA, proteins, and carbohydrates. The properties and functions of these molecules are determined by the types of covalent bonds they contain. For instance, the structure of enzymes and their ability to catalyze reactions depend on the specific arrangement of covalent bonds. Additionally, the behavior of cell membranes, which are composed of phospholipids with polar and nonpolar regions, is influenced by covalent bonding. Thus, knowledge of covalent bonds is essential for understanding molecular interactions and biological processes.