Problem 79 - Chemistry The Science in Context

Question

Chemists can use the octet rule to predict the structures of new compounds to synthesize. Draw Lewis structures showing all resonance forms for the hypothetical compound ClSeNSO, where the atoms are connected in the order they are written.

Step-by-Step Solution

Answer

Answer: The Lewis structure for ClSeNSO is as follows: O : S - N = Se - Cl : O Each atom in the compound follows the octet rule, having 8 electrons around each atom.

Step 1: Determine the total number of valence electrons

To draw the Lewis structures, we first need to find the total number of valence electrons present in the compound. For each atom, refer to the periodic table to find the number of valence electrons and then add them together. - Cl (Chlorine) has 7 valence electrons - Se (Selenium) has 6 valence electrons - N (Nitrogen) has 5 valence electrons - S (Sulfur) has 6 valence electrons - O (Oxygen) has 6 valence electrons Total valence electrons = 7 + 6 + 5 + 6 + 6 = 30 valence electrons

Step 2: Connect the atoms with single bonds

Now that we have the total number of valence electrons, we can start with connecting the atoms in the given order (ClSeNSO) using a single bond (which represents two electrons). For each single bond formed, we will subtract 2 electrons from the total valence electrons. Since we have 4 single bonds, we will have 4 x 2 = 8 less electrons. Remaining electrons = 30 - 8 = 22 electrons

Step 3: Distribute the remaining electrons

With the 22 remaining electrons, add them to the atoms to fulfill the octet rule (8 electrons for each atom except Hydrogen, which is not involved here). First, fill the octet of outer atoms (Cl, N, S, and O), then the central atom (Se). After allocating the electrons, we have the following situation: - Cl (7): 6 additional electrons - Se (6): 4 additional electrons - N (5): 4 additional electrons - S (6): 6 additional electrons - O (6): 6 additional electrons

Step 4: Check the octet rule for each atom

Now, verify whether all atoms follow the octet rule (having 8 electrons around each atom): - Cl has 2 (from the bond with Se) + 6 (additional electrons) = 8 electrons (Satisfied) - Se has 2 (from the bond with Cl) + 2 (from the bond with N) + 4 (additional electrons) = 8 electrons (Satisfied) - N has 2 (from the bond with Se) + 2 (from the bond with S) + 4 (additional electrons) = 8 electrons (Satisfied) - S has 2 (from the bond with N) + 2 (from the bond with O) + 6 (additional electrons) = 8 electrons (Satisfied) - O has 2 (from the bond with S) + 6 (additional electrons) = 8 electrons (Satisfied) Because all atoms are following the octet rule, the Lewis structure of ClSeNSO is: O : S - N = Se - Cl : O

Key Concepts

Octet Rule

Understanding the octet rule is essential for grasping how atoms bond together to form molecules. The octet rule is a chemical rule of thumb that states that atoms tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas. The significance of this rule lies in the stability associated with the electronic structure of noble gases.

Explaining this in the context of the hypothetical compound ClSeNSO, during the Lewis structure drawing process, atoms bond together to fulfill their octet, meaning they aim to reach an arrangement of eight electrons around them. Hydrogen is an exception to this rule as it only requires two electrons to fill its valence shell.

When we follow the octet rule for ClSeNSO, we distribute electrons after forming the initial single bonds to ensure that Cl, Se, N, S, and O all have access to eight electrons. By adhering to this rule, we can deduce the most stable structure for a molecule.

Valence Electrons

Valence electrons are the electrons in the outermost shell, or energy level, of an atom that participate in forming chemical bonds. In the context of Lewis structures, knowing the number of valence electrons is crucial for predicting how atoms will combine and for drawing accurate models of molecules.

For the exercise involving ClSeNSO, we determine the total number of valence electrons as follows:

• Cl (Chlorine) has 7 valence electrons,
• Se (Selenium) has 6,
• N (Nitrogen) has 5,
• S (Sulfur) has 6,
• O (Oxygen) also has 6.

By adding up all the valence electrons from each atom, we get a sum of 30. These are the electrons available to be shared or shifted between the atoms to form a stable molecule while adhering to the octet rule. Without this step, it would be impossible to correctly illustrate the bonds and lone pairs in the molecule's Lewis structure.

Resonance Forms

Resonance forms are a way of describing delocalized electrons within certain molecules where the bonding cannot be expressed by a single Lewis structure. Instead, multiple structures, called resonance forms, are used to represent the molecule's electronic structure. The true form of the molecule is a hybrid of all the resonance forms.

In the molecule ClSeNSO, if we encounter a situation where electrons can be distributed in more than one viable way while still adhering to the octet rule, we would have resonance forms. These different structures do not represent distinct entities but are visual tools that help us understand the molecule's flexibility in electron sharing and distribution.

When drawing resonance forms, it is important to remember that only the arrangement of electrons can differ; the positions of the atoms must remain constant. Double-headed arrows are typically used to indicate the equivalence between these forms, signifying that the molecule's actual electronic structure is an averaged amalgamation of the resonance forms.