Lewis Dot Structures: Multiple Bonds: Videos & Practice Problems

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 this, sharing electrons effectively. Each nitrogen atom in a triple bond has eight electrons, fulfilling the octet requirement. It's important to note that 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 organic chemistry.

Lewis Dot Structures: Multiple Bonds Concept 1

Atoms often form multiple bonds when their valence electrons are insufficient to satisfy the octet rule, which states that atoms ideally seek to have eight electrons in their outer shell, similar to the electron configuration of noble gases. For instance, consider nitrogen, which can form either a single bond or a triple bond with another nitrogen atom. In the case of a single bond, a total of 10 valence electrons are utilized: each single bond consists of 2 electrons, leading to a count of 2, 4, 6, 8, and finally 10. However, this configuration leaves both nitrogen atoms with an incomplete octet, as each nitrogen only has 6 electrons surrounding it (2, 4, 6). To resolve this issue, forming a triple bond is more effective. In this arrangement, the total remains at 10 valence electrons, but now each nitrogen atom achieves a complete octet with 8 electrons (2, 4, 6, 8).

It is crucial to remember that multiple bonds, such as double or triple bonds, may be necessary to fulfill the octet rule for certain atoms. However, hydrogen is an exception; it adheres to the duet rule, desiring only 2 electrons in its outer shell to achieve a stable configuration akin to helium.

Lewis Dot Structures: Multiple Bonds Example 1

To draw the Lewis dot structure for the formaldehyde molecule (CH₂O), we begin by calculating the total number of valence electrons. Carbon, located in group 4A, contributes 4 valence electrons. Each hydrogen, found in group 1A, contributes 1 valence electron, and since there are two hydrogens, that totals 2 valence electrons. Oxygen, from group 6A, adds 6 valence electrons. Summing these gives us:

4 (from C) + 2 (from H) + 6 (from O) = 12 valence electrons.

Next, we place the least electronegative atom in the center, which in this case is carbon, as hydrogen cannot occupy the central position. We connect the carbon atom to the two hydrogen atoms with single bonds and to the oxygen atom, also with a single bond. This arrangement looks like this:

H - C - H

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O

Following the octet rule, we add electrons to surrounding atoms until they achieve a full outer shell. Hydrogen follows the duet rule, requiring only 2 electrons. We distribute the remaining electrons, ensuring that each hydrogen has 2 electrons and that carbon and oxygen work towards achieving their octets. After placing 6 electrons around the oxygen, we find that we have used 12 electrons in total:

8 (for H) + 2 (for C) + 6 (for O) = 12 electrons used.

Since carbon only has 6 electrons around it (2 from each bond with hydrogen and 2 from the bond with oxygen), it does not satisfy the octet rule. To remedy this, we can form a double bond between carbon and oxygen. We take one of the lone pairs from oxygen and convert it into a bond with carbon. This adjustment allows carbon to have 4 bonds (2 with hydrogen and 2 with oxygen), thus satisfying its bonding preference.

The final Lewis structure for formaldehyde is represented as:

H - C = O

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H

In this structure, carbon is single bonded to both hydrogens and double bonded to oxygen, which retains two lone pairs of electrons. This configuration fulfills the octet rule for carbon and oxygen while adhering to the duet rule for hydrogen, resulting in a stable molecular structure for formaldehyde.

Draw the Lewis Dot Structure for CO₂ compound.

• A.
• B.
• C.
• D.

Answer: (C)

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

To draw the Lewis dot structure for the diazine molecule, we first need to calculate the total number of valence electrons. Nitrogen, which is in group 5A, contributes 5 electrons each, and since there are two nitrogen atoms, that gives us a total of 10 electrons. Hydrogen, found in group 1A, contributes 1 electron each, and with two hydrogen atoms, we add 2 more electrons. Therefore, the total number of valence electrons is:

Total Valence Electrons = 10 (from N) + 2 (from H) = 12 electrons

In constructing the structure, hydrogen cannot occupy the central position, so we place the two nitrogen atoms in the center. Since hydrogen can only form single bonds, we connect each hydrogen atom to a nitrogen atom. This initial bonding uses 6 electrons (2 for each bond), leaving us with:

Remaining Electrons = 12 - 6 = 6 electrons

Next, we distribute the remaining electrons. Initially, we place the remaining 6 electrons as lone pairs around the nitrogen atoms. However, we notice that the nitrogen on the right does not satisfy the octet rule, having only 6 electrons around it. To resolve this, we can form a double or triple bond. In this case, we take one of the lone pairs from the nitrogen on the left and use it to create a triple bond between the two nitrogen atoms.

After adjusting for the triple bond, both nitrogen atoms now have 8 electrons around them, fulfilling the octet rule. The hydrogen atoms still only require 2 electrons each, resembling helium. Thus, the final Lewis dot structure for the diazine molecule is correctly represented, ensuring all atoms satisfy their respective electron requirements.

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

• A.
• B.
• C.
• D.

Answer: (B)

Here’s what students ask on this topic:

What is the octet rule and why is it important in Lewis dot structures?

The octet rule states that atoms tend to form bonds until they are surrounded by eight valence electrons, achieving a stable electron configuration similar to noble gases. This rule is crucial in Lewis dot structures because it helps predict how atoms will bond and arrange themselves in molecules. For example, in a nitrogen molecule (N₂), each nitrogen atom forms a triple bond to ensure both have eight electrons in their valence shells. Understanding the octet rule allows students to draw accurate Lewis structures and predict molecular behavior.

How do multiple bonds help satisfy the octet rule in Lewis structures?

Multiple bonds, such as double and triple bonds, help satisfy the octet rule by allowing atoms to share more electrons. For instance, in a nitrogen molecule (N₂), each nitrogen atom shares three pairs of electrons, forming a triple bond. This sharing ensures that each nitrogen atom has eight electrons in its valence shell, fulfilling the octet rule. Without multiple bonds, atoms might not achieve the stable electron configuration they need, leading to incomplete octets and less stable molecules.

Why does hydrogen not follow the octet rule in Lewis dot structures?

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. In Lewis dot structures, hydrogen forms a single bond, sharing one pair of electrons with another atom. This allows hydrogen to have two electrons in its valence shell, which is sufficient for its stability. Understanding this exception is important for accurately drawing Lewis structures involving hydrogen.

Can you explain the difference between single, double, and triple bonds in Lewis structures?

In Lewis structures, single, double, and triple bonds represent different levels of electron sharing between atoms. A single bond involves one pair of shared electrons (2 electrons), a double bond involves two pairs of shared electrons (4 electrons), and a triple bond involves three pairs of shared electrons (6 electrons). For example, in a nitrogen molecule (N₂), a triple bond is formed, sharing three pairs of electrons between the two nitrogen atoms. These multiple bonds help atoms achieve the octet rule, ensuring stability in the molecule.

How do you determine the number of valence electrons in a molecule for drawing Lewis dot structures?

To determine the number of valence electrons in a molecule, sum the valence electrons of each atom in the molecule. For example, in a water molecule (H₂O), oxygen has 6 valence electrons, and each hydrogen has 1 valence electron. Therefore, the total number of valence electrons is 6 (from O) + 1 (from H) + 1 (from H) = 8 valence electrons. This total helps in drawing the Lewis dot structure, ensuring that the electrons are distributed to satisfy the octet rule (or duet rule for hydrogen).