Problem 70 - Chemistry

Question

Oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\), is a mildly poisonous substance found in the leaves of rhubarb, spinach, and many other plants. (You'd have to eat about \(15 \mathrm{lbs}\). or so of spinach leaves to ingest a lethal amount.) If oxalic acid has a \(\mathrm{C}-\mathrm{C}\) single bond and no \(\mathrm{C}-\mathrm{H}\) bond, draw its electron-dot structure showing lone pairs and identifying any multiple bonds.

Step-by-Step Solution

Answer

The electron-dot structure includes two \(\mathrm{C}=\mathrm{O}\) double bonds with lone pairs on each oxygen, and a \(\mathrm{C}-\mathrm{C}\) single bond.

Step 1: Count Total Valence Electrons

First, determine the total number of valence electrons in oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\). Carbon (C) has 4 valence electrons, hydrogen (H) has 1, and oxygen (O) has 6. Therefore, the total is \((2 \times 4) + (2 \times 1) + (4 \times 6) = 24\) valence electrons.

Step 2: Create a Skeleton Structure

Next, arrange the atoms to reflect the structure with a \(\mathrm{C}-\mathrm{C}\) bond by placing the two carbons in the center, each connected to two oxygens and one hydrogen. The initial arrangement is: \[\mathrm{H}-\mathrm{C}-\mathrm{C}-\mathrm{O}-\mathrm{O}\]

Step 3: Distribute Electrons to Form Bonds

Allocate the 24 valence electrons starting by forming covalent bonds. Place each electron pair between atoms: \(\mathrm{H}-\mathrm{C}\), \(\mathrm{C}-\mathrm{C}\), \(\mathrm{C}-\mathrm{O}\), and between \(\mathrm{C}-\mathrm{O}\) for each oxygen bonded to carbon atoms.

Step 4: Create Double Bonds

Distribute the remaining electrons to satisfy the octet rule for each atom. Add double bonds between the carbon and the remaining oxygens: \[\mathrm{H}-\mathrm{C}=\mathrm{O}, \; \mathrm{O}=\mathrm{C}-\mathrm{C}=\mathrm{O},\; \mathrm{O}-\mathrm{H}\]

Step 5: Add Lone Pairs

Finally, add lone pairs around the oxygens to complete their octet. Each oxygen should have 8 valence electrons around it, including bonding and non-bonding pairs. Ensure each hydrogen has a full valence of 2 electrons.

Key Concepts

Oxalic Acid

Oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\), is an organic compound with intriguing properties. It is a simple dicarboxylic acid, meaning it contains two carboxyl groups (\(\mathrm{-COOH}\)) per molecule. You can find it naturally in many plants like spinach and rhubarb. Despite being mildly toxic, it's important to understand its molecular structure to appreciate its potential applications in chemistry and industry.
Understanding the electron-dot structure of oxalic acid gives insight into how its atoms are bonded and how electrons are distributed. Knowing the basics helps you comprehend the chemical properties and reactivity of this compound. Oxalic acid does not have \(\mathrm{C}-\mathrm{H}\) bonds which influences its structural layout. By drawing its electron-dot structure, you can visualize its unique bonding features.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in bond formation. They determine how atoms interact and bond with each other. For oxalic acid, the valence electrons contribute to forming the chemical bonds between its atoms.

• Carbon (C) has 4 valence electrons.
• Hydrogen (H) has 1 valence electron.
• Oxygen (O) has 6 valence electrons.

Calculating the total number of valence electrons in oxalic acid involves summing each atom's valence electrons: \[(2 \times 4) + (2 \times 1) + (4 \times 6) = 24 \, \text{valence electrons}\]Using these electrons, you can properly arrange and design the compound's electron-dot structure, ensuring all atoms achieve a stable electron configuration.

Double Bond

A double bond represents a stronger link between two atoms than a single bond, involving two shared pairs of electrons. In the oxalic acid structure, double bonds help fulfill the octet rule for the carbon and oxygen atoms.
When building the electron-dot structure of oxalic acid, it's essential to know where these double bonds occur. In oxalic acid, the primary double bonds are:

• Between carbon and oxygen in the \(\mathrm{C} = \mathrm{O}\) group
• Within the structural layout: \(\mathrm{H}-\mathrm{C}=\mathrm{O}, \; \mathrm{O}=\mathrm{C}-\mathrm{C}=\mathrm{O},\; \mathrm{O}-\mathrm{H}\)

The presence of double bonds affects the molecule's reactivity and stability. Understanding where these bonds form aids in predicting the behavior of the compound when reacting with other substances.

Lone Pairs

Lone pairs are non-bonding pairs of valence electrons that do not participate in bonding. They play a significant role in determining the shape and reactivity of a molecule.
In oxalic acid, lone pairs are found primarily around the oxygen atoms. When completing the electron-dot structure, each oxygen atom needs to satisfy the octet rule, meaning it should have eight electrons around itself, including both those in bonds and as lone pairs.

• These lone pairs contribute to the full valence shell for the oxygen atoms.
• The presence of lone pairs can influence the molecular geometry and the acid's interaction with other molecules.

Accurately placing lone pairs in the electron-dot structure is crucial for modeling how oxalic acid might behave chemically. Their distribution can enhance understanding of molecular polarity and potential hydrogen bonding.