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 due to similar electronegativities, while polar covalent bonds exhibit unequal sharing, resulting in partial charges. For example, in water (H₂O), oxygen's high electronegativity leads to a partial negative charge, while hydrogen atoms acquire partial positive charges. Understanding these concepts is crucial for grasping molecular interactions and properties in chemistry.

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 simply means the sharing of electrons. If electrons are being shared between two different atoms, then we have ourselves a covalent bond. Electrons being shared between atoms can be shared in two different ways. This leads to two different types of covalent bonds that share electrons in different ways. The first type of covalent bond that you should know is the nonpolar covalent bond, and then 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 covalent bonds 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 to 4 at its maximum. An electronegativity of 0 means that an atom is not very electronegative at all and does not pull hard on electrons. Whereas an electronegativity value closer to 4 means that the atom is very electronegative and pulls really hard on electrons. When you 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 values of electronegativities. You can see that underneath, the numbers represent the electronegativity values of these atoms. Notice also that atoms increase in electronegativity from bottom to top in any column. Starting at the bottom and making your way to the top, the atoms become more and more electronegative. This is the reason for the two different types of covalent bonds.

It's not necessary to memorize all these electronegativity values, but it is crucial to recognize 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 particularly important when we start to talk about the water molecule later in our course, which has one oxygen atom. Oxygen's high electronegativity makes it pull very hard on electrons. This concludes our introduction to covalent bonds, and moving forward, we will 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

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. In this video, we're going to talk about our first type of covalent bonds which are the nonpolar covalent bonds. Nonpolar covalent bonds are, of course, 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. There will be sharing of electrons between atoms in nonpolar covalent bonds. The term nonpolar is a term that refers to equality, 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 due to the equal or similar electronegativities of the atoms involved in the nonpolar covalent bond. 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.

If we take a look at our image below, we'll be able to see 3 different examples of nonpolar covalent bonds. Each person in this little interesting image represents an atom. There are 2 atoms here sharing this electron between them equally. In our first example, we have a molecule called hydrogen gas whose chemical formula is H₂, meaning that it consists of 2 hydrogen atoms. There is a line between these 2 hydrogen atoms, which represents a covalent bond. In this case, it represents a nonpolar covalent bond because these 2 identical hydrogen atoms have equal electronegativities, which means that they pull equally on this shared pair of electrons between them. Thus, those electrons will be shared equally between the 2 atoms. Equal sharing of electrons between atoms results in nonpolar covalent bonds.

The next example is a molecule called oxygen gas whose chemical formula is O₂. It consists of 2 identical oxygen atoms sharing, in this case, 2 pairs of electrons in a double bond, which is why you see two lines between those 2 oxygen atoms. These 2 covalent bonds are nonpolar covalent bonds because those 2 pairs of electrons are being shared equally between those 2 identical atoms. These 2 identical oxygen atoms have equal electronegativities and thus pull equally on those 2 shared pairs of electrons.

In our last example, unlike the first two examples where the atoms were identical, this example involves different types of atoms or different elements. We have a carbon atom and 4 hydrogen atoms; this is the molecule methane. The carbon atom is central, and the 4 hydrogen atoms are around the carbon atom, each bonded to the central carbon atom via nonpolar covalent bonds. There are 4 nonpolar covalent bonds linking each of the 4 hydrogen atoms to the carbon. These bonds are nonpolar covalent bonds because the carbon and hydrogen atoms have very similar electronegativities. They are not identical, but they are similar enough that those electrons are shared relatively equally, creating a nonpolar covalent bond.

Here we see another image depicting an electron represented as e^- in the middle of a tug-of-war match; each person represents an atom. This shows that the two people are pulling equally on the electron, symbolizing equal sharing in nonpolar covalent bonds, a key takeaway here. This concludes our brief introduction to nonpolar covalent bonds. We'll be able to get some practice as we move forward and then we'll discuss polar covalent bonds. 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 our first type of covalent bond, the nonpolar 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 going to have a partial positive charge because it pulls 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 going to be shared unequally leading to these polar covalent bonds. And so, notice that the oxygen atom that pulls harder on electrons is going to have the negatively charged electrons for more time so it gains a partial negative charge. And each of the hydrogen atoms is, going to 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 NH₃. 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 going to 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.

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 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 molecules and are crucial for the structure and function of biological macromolecules.

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. Water (H₂O) is a classic example of a molecule with polar 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. It plays a crucial role in the formation of covalent bonds. When two atoms with similar electronegativities form a bond, they share electrons equally, resulting in a nonpolar covalent bond. However, when there is a significant difference in electronegativity between the two atoms, the electrons are shared unequally, leading to a polar covalent bond. The more electronegative atom pulls the shared electrons closer, creating a partial negative charge, while the less electronegative atom has a partial positive charge.

Why is water considered a polar molecule?

Water (H₂O) is considered a polar molecule because of the significant difference in electronegativity between oxygen and hydrogen atoms. Oxygen has a much higher electronegativity compared to hydrogen, causing the shared electrons in the covalent bonds to be pulled closer to the oxygen atom. This unequal sharing of electrons results in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. The bent shape of the water molecule further accentuates this polarity, making water an excellent solvent for many substances.

What are some examples of molecules with nonpolar covalent bonds?

Examples of molecules with nonpolar covalent bonds include hydrogen gas (H₂), oxygen gas (O₂), and methane (CH₄). In hydrogen gas, two hydrogen atoms share electrons equally because they have identical electronegativities. Similarly, in oxygen gas, two oxygen atoms share electrons equally. In methane, the carbon and hydrogen atoms have similar electronegativities, leading to relatively equal sharing of electrons and nonpolar covalent bonds. These molecules are characterized by the absence of partial charges and are generally less reactive than polar molecules.