Lewis Dot Structures: Multiple Bonds - Online Tutor, Practice Problems & Exam Prep

Atoms often form multiple bonds, such as double or triple bonds, to satisfy the octet rule, which states that atoms prefer to have eight electrons in their valence shell. For example, nitrogen can form a triple bond to achieve a complete octet, utilizing 10 valence electrons while ensuring each nitrogen has eight electrons around it. Unlike nitrogen, hydrogen follows the duet rule, desiring only two electrons to resemble helium. Understanding these bonding principles is crucial for grasping molecular structures and reactivity in chemistry.

Lewis Dot Structures: Multiple Bonds Concept 1

Here, we're going to say that atoms form multiple bonds when valence electrons are not enough to satisfy the octet. So we're talking about the octet rule, where one element ideally wants to have 8 electrons around it, so it can help fulfill the same type of electron arrangement as a noble gas. Here if we take a look, we have nitrogen shown with a single bond between the two nitrogens or a triple bond between them. Looking at the differences, we can say here that each nitrogen in the first structure, we have a total of 10 valence electrons being used. Remember, a single bond has 2 electrons in it, so that'd be 2, 4, 6, 8, 10. We have 10 valence electrons. But we run into an issue. Both nitrogens have an incomplete octet. Remember when we have a covalent bond, we're sharing the electrons within that covalent bond with each other. So, the nitrogen on the left has 2, 4, 6 electrons around it. And the same thing can be said with the nitrogen on the right. It has 2, 4, 6 electrons around it. It's not fulfilling its octet rule. To deal with this, it's better to create a triple bond between the two nitrogens. So, they still have 10 valence electrons because we have 2, 4, 6, 8, 10. And this is the better way of drawing it because each nitrogen has 2, 4, 6, 8 electrons around them. So just remember, sometimes we'll have to create multiple bonds, double bonds, possibly triple bonds, in order to fulfill the octet rule for any given atom. Now remember, hydrogen doesn't fit here. Hydrogen does not follow the octet rule. It follows the duet rule, where it only wants to have 2 electrons around it so they can resemble helium.

Lewis Dot Structures: Multiple Bonds Example 1

Here we need to draw the Lewis dot structure for the formaldehyde molecule, which is CH₂O. We're going to start out with step 1, which says to determine the total number of valence electrons of the structure. So hydrogen, carbon, oxygen. Carbon is in group 4A, there's one of it, so that's 4 valence electrons. We have hydrogen, 2 hydrogens, each one's in group 1A, so that's 2 valence electrons. And then we have oxygen, which is in group 6A, and there's one of it, so that's 6 valence electrons. That comes out as a total of 12 valence electrons. Because remember, the group number equals the number of valence electrons. Next, we're going to place the least electronegative element in the center and connect all elements with single bonds. To do this, we're going to follow our bonding preferences guide to determine atom connectivity. Now remember, hydrogen cannot go in the center, so next up would be carbon. Here to deal with symmetry, I'm just doing single bonds with the hydrogens on both sides, and then oxygen up here.

Next, we're going to add electrons to all surrounding elements until they have 8 electrons because we're talking about the octet rule, except for hydrogen which follows the duet rule. It only wants 2 valence electrons around it. Okay. So let's do that. We're going to add electrons, so 1, 2, 3, 4, 5, 6. And remember in a covalent bond we're sharing electrons, so that's 8. Alright. How many electrons have we used? That's 8 there, 10, 12. We've used all 12 of our electrons, so we have none left. Now place any remaining electrons of the central atom, which we cannot because there's no more. Now if any elements don't have 8 octet electrons, add double or triple bonds between them. Alright. So this carbon here only has 2, 4, 6 electrons around it. Remember the bonding preferences of carbon is that carbon wants to make 4 bonds. Oxygen ideally wants to make 2 bonds. So for them to do that, what I'm gonna do is I'm gonna take one of these lone pairs here, and then just bring it down to help make a double bond. And by doing that, I'm still using the 12 electrons that I have total, but carbon is being satisfied by making 4 bonds and so is oxygen. So this would be the formula for the formaldehyde molecule. Carbon is single bonded to both hydrogens, double bonded to the oxygen. Oxygen itself has 2 lone pairs. So this would be the correct structure for formaldehyde.

Draw the Lewis Dot Structure for CO₂ compound.

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Determine the Lewis Dot Structure for the diazene molecule, N₂H₂.

Here it says to draw the Lewis dot structure for the diazine molecule. So, we're going to figure out how many valence electrons we have in total. Nitrogen is in group 5A, and there are 2 of them. Hydrogen is in group 1A, and there are 2 of them. So, it's going to be 10 + 2 which is 12. Hydrogen can't go in the center, so it's going to be the 2 nitrogens. Remember, hydrogens only make single bonds. So right now we've used a total of 2, 4, 6 electrons, meaning we have 6 electrons remaining. Alright. So then what do we do? We have 1, 2, 3, 4, 5, 6. We've used all of our electrons, but we have an issue. The nitrogen on the left has 8 electrons around it total, which is great, but then the one on the right doesn't. It has 2, 4, 6. Remember, if an atom is not following the octet rule and it needs to, we can make double or triple bonds. So that's what we're going to do. We're going to take one of these lone pairs and use it to make a triple bond. So here are our electrons that we had before, and I took one of the lone pairs here to make a double bond. And in that way, both nitrogens are fulfilling the octet rule. Again, hydrogen only needs 2 electrons around it because it wants to resemble helium. So this would represent the correct Lewis dot structure of the diazine molecule.

Give the Lewis Dot Structure that obeys the octet rule for following compound:NOCl.

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Here’s what students ask on this topic:

What is the octet rule in chemistry?

The octet rule in chemistry states that atoms tend to form bonds in such a way that each atom has eight electrons in its valence shell, achieving a stable electron configuration similar to that of noble gases. This rule is a guiding principle for understanding how atoms bond and form molecules. For example, in a molecule of nitrogen (N₂), each nitrogen atom shares three pairs of electrons, forming a triple bond to satisfy the octet rule. However, there are exceptions, such as hydrogen, which follows the duet rule and seeks only two electrons to resemble helium.

Why do atoms form multiple bonds?

Atoms form multiple bonds, such as double or triple bonds, to satisfy the octet rule when single bonds are insufficient. For instance, in a nitrogen molecule (N₂), a single bond would leave each nitrogen atom with only six electrons, failing to meet the octet rule. By forming a triple bond, each nitrogen atom shares three pairs of electrons, ensuring that both have eight electrons in their valence shells. This arrangement provides greater stability to the molecule.

How do you determine the number of valence electrons in a molecule?

To determine the number of valence electrons in a molecule, sum the valence electrons of each atom in the molecule. For example, in a nitrogen molecule (N₂), each nitrogen atom has five valence electrons. Therefore, the total number of valence electrons is 5 + 5 = 10. This total helps in drawing the Lewis dot structure and understanding how atoms bond to satisfy the octet rule.

What is the difference between a single, double, and triple bond?

A single bond involves the sharing of one pair of electrons between two atoms, a double bond involves two pairs, and a triple bond involves three pairs. For example, in a nitrogen molecule (N₂), a single bond would share one pair of electrons, a double bond would share two pairs, and a triple bond shares three pairs of electrons. Multiple bonds (double and triple) are formed to satisfy the octet rule when single bonds are insufficient.

Why does hydrogen not follow the octet rule?

Hydrogen does not follow the octet rule because it only needs two electrons to achieve a stable electron configuration, resembling helium. This is known as the duet rule. Hydrogen has only one electron in its valence shell, and by forming a single bond with another atom, it shares one more electron, achieving a total of two electrons, which is sufficient for its stability.