Question

Oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\), is a poisonous compound found in rhubarb leaves. Draw the Lewis structure for oxalic acid. There is a single bond between the two carbon atoms, each hydrogen atom is bonded to an oxygen atom, and each carbon is bonded to two oxygen atoms.

Short answer

The correct Lewis structure for oxalic acid is as follows: O-H:6 || C=O | C=O || O-H:6 Each carbon atom is bonded to two oxygen atoms, with one oxygen atom forming a double bond. Additionally, each hydrogen atom is bonded to a separate oxygen atom, and all atoms (except hydrogen) satisfy the octet rule.

Step-by-step solution

Count the total number of valence electrons

Before drawing the Lewis structure, we should find the total number of valence electrons for each atom in oxalic acid molecule. For each hydrogen atom, there is 1 valence electron, for each carbon atom, there are 4 valence electrons, and for each oxygen atom, there are 6 valence electrons. The total valence electrons in oxalic acid are: (2 * 1) + (2 * 4) + (4 * 6) = 2 + 8 + 24 = 34

Arrange the atoms

Next, arrange the atoms in a skeleton structure. We can start with the carbon atoms in the center on the basis of the clue provided: a single bond between them. In addition, each carbon atom should be bonded to two oxygen atoms, and each hydrogen atom must bond to an oxygen atom. The arrangement will look like: O-H | C-O | C-O | O-H

Distribute the electrons

Distribute the remaining 28 valence electrons (34 total, minus 6 from single bonds) as lone pairs around the oxygen atoms to satisfy their octets: O-H:8 | C-O:8 | C-O:8 | O-H:8

Complete the bonding

Now, check if all atoms satisfy the octet rule (hydrogen has a duet rule). Carbon atom doesn't have an octet; it has only 6 electrons now. To correct this, we will turn one lone pair on each oxygen atom into a double bond with the carbon atom: O-H:6 || C=O | C=O || O-H:6 Now all atoms (except hydrogen, of course) satisfy the octet rule, and we have the complete Lewis structure for oxalic acid.

Key concepts

Valence Electrons in Chemical Bonding

Valence electrons are the outermost electrons of an atom and play a pivotal role in chemical bonding. In the context of creating the Lewis structure for oxalic acid, we first calculate the total number of valence electrons available to determine how atoms can bond with each other. For oxalic acid, \text{(H\(_{2}\)C\(_{2}\)O\(_{4}\))},we found that hydrogen has 1 valence electron, carbon has 4, and oxygen has 6. After multiplying these by the number of each atom and summing them up, we get a total of 34 valence electrons.These electrons are the 'currency' for creating bonds between atoms. When we distribute them, we aim to ensure that most atoms achieve a stable electronic configuration, generally by filling their outermost shells with electrons, following the guidance of the octet rule. Valence electrons form both the bonding pairs, which link atoms together, and the non-bonding pairs, or 'lone pairs', which complete an atom's valence shell but don't contribute to bonding directly with other atoms.

The Octet Rule in Lewis Structures

The octet rule states that atoms tend to form bonds until they are surrounded by eight valence electrons, resulting in a configuration similar to that of the noble gases, known for their stability. When we draw the Lewis structure of oxalic acid, this rule helps us to distribute the electrons correctly.Hydrogen is an exception to this rule as it follows the 'duet rule,' preferring to have only two electrons in its outer shell. Thus, in our Lewis structure for oxalic acid, each hydrogen atom forms a single bond with an oxygen atom.The octet rule is satisfied for each oxygen atom by distributing the remaining electrons as lone pairs after accounting for bond formation. For the carbon atoms in oxalic acid, applying the octet rule helped us identify the need for double bonds with oxygen to ensure that carbon too has eight electrons in its valence shell.

Understanding Chemical Bonding

Chemical bonding is the process that holds atoms together in molecules. When drafting the Lewis structure for oxalic acid, the bonds depicted are a result of atoms sharing or transferring valence electrons. Oxalic acid primarily displays two types of bonding:

• Covalent bonding - where atoms share pairs of electrons, as seen in the single and double bonds within the molecule.
• Polar covalent bonding - commonly occurs in acids like oxalic acid, where there's a difference in electronegativity between bonded atoms, such as the bonds between hydrogen and oxygen.

Through the step-by-step process, we determined the arrangement of single and double bonds to ensure that all atoms achieve their desired stable configuration. It is these shared electrons that fulfill the octet rule for the carbon and oxygen atoms. In oxalic acid, each carbon shares electrons with two oxygens, and we identified that a double bond was necessary to complete carbon's octet, thus demonstrating how understanding valence electrons and chemical bonding can elucidate the structure of a molecule.