Question

Oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\), a poisonous colorless solid, is found in some vegetables such as spinach and rhubarb. It is present in concentrations well below the toxic limit, so you can't use this as a reason to refuse a helping of spinach. The order of atoms in a molecule of oxalic acid is \(\mathrm{HO}_{2} \mathrm{CCO}_{2} \mathrm{H}\). How many unshared pairs of electrons are on the carbon and oxygen atoms?

Short answer

The number of unshared pairs of electrons on the carbon and oxygen atoms in a molecule of oxalic acid is 8

Step-by-step solution

Identify the valence electrons of Oxygen and Carbon

From the periodic table, we can gather that Oxygen has 6 valence electrons and Carbon has 4 valence electrons.

Understand the distribution of electrons in the molecule

In oxalic acid, there is a distribution of electrons between carbon and oxygen atoms. Each carbon atom forms a double bond with oxygen atom, which means each carbon atom shares 4 electrons with those oxygen atoms. For oxygen, it shares 2 electrons to form double bonds with carbon, leaving it 4 unshared valence electrons.

Calculate the number of unshared pairs

Each molecule of Oxalic acid has 2 carbon atoms and 4 oxygen atoms. Since each Carbon atom has no unshared pair (as all are involved in bonding) and each oxygen atom has 2 unshared pairs (4 electrons), total number of unshared pairs = 2 (unshared pair in each oxygen) * 4 (total oxygen atoms)= 8.

Key concepts

Valence Electrons

When we talk about valence electrons, we're referring to the electrons that are in the outermost shell of an atom. These electrons play a critical role in chemical reactions because they can be gained, lost, or shared in the process of chemical bonding. In the case of oxalic acid, which has the molecular formula \( \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \), understanding the valence electrons is key to determining its molecular structure and reactivity.

For instance, carbon (C), which resides in group 14 on the periodic table, has four valence electrons, whereas oxygen (O), found in group 16, has six valence electrons. These information bits provide insight into how these atoms will bond and interact within a molecule like oxalic acid. With these basics in mind, it becomes easier to comprehend why each carbon in oxalic acid forms double bonds with oxygen, utilizing all of its valence electrons for bonding.

Molecular Structure

Examining the molecular structure reveals the arrangement of atoms within a molecule. For oxalic acid, its molecular structure can be represented by the formula \( \mathrm{HO}_{2} \mathrm{CCO}_{2} \mathrm{H} \), which informs us of the order in which the hydrogen, carbon, and oxygen atoms are connected. This sequence is essential to determine the molecule's shape, bond angles, and overall geometry.

The carbon atoms in oxalic acid are each bonded to two oxygen atoms by double bonds, which are key to the molecule's planar (flat) structure. Each oxygen atom also has two unshared pairs of electrons, contributing to the molecule's properties, such as its polar nature and the capacity to form hydrogen bonds with other molecules. A clear understanding of the molecular structure helps in predicting a substance's reaction pathways and its physical and chemical characteristics.

Electron Distribution

Electron distribution within a molecule determines the placement of electrons, both shared and unshared. It influences the molecule's electrical charge distribution and its potential interaction with other molecules. In oxalic acid, the electron distribution is such that the four oxygen atoms have unshared pairs, while the carbon atoms do not have unshared pairs due to their involvement in double bonds.

Steps to Analyze Electron Distribution:

• Assess the valence electrons for each atom.
• Understand how atoms bond within the molecule.
• Calculate unshared (lone) pairs of electrons.

As calculated in the exercise solution, each oxygen atom in oxalic acid has two unshared pairs of electrons, totaling eight unshared pairs in the molecule. Such an electron distribution pattern can affect molecular interactions, the physical state, and even the acidity of oxalic acid.

Chemical Bonding

Chemical bonding is fundamental in chemistry as it explains how atoms are held together in a molecule. The bonds in oxalic acid, for instance, are covalent, meaning atoms share pairs of electrons. The carbon atoms bond with the oxygen atoms through double bonds, which involves sharing two pairs of electrons between them.

Types of Chemical Bonds:

• Covalent bonds: Atoms share electron pairs.
• Ionic bonds: Atoms transfer electrons.
• Metallic bonds: Electrons are delocalized within a metal lattice.

The covalent bonding between C and O in oxalic acid dictates its molecular stability, solubility, and how it reacts with other substances. These bonds also affect the molecule's energy states and how it releases or absorbs energy during a reaction. Chemical bonding, as a topic, underpins nearly every chemical process, making it crucial for students to grasp in order to understand more complex chemical systems.