Problem 41 - Chemistry An Atoms First Approach

Question

Use the localized electron model to describe the bonding in \(\mathrm{H}_{2} \mathrm{CO}\) (carbon is the central atom).

Step-by-Step Solution

Answer

In H₂CO, the Lewis structure has a central carbon atom single-bonded to hydrogen and double-bonded to oxygen. The carbon atom exhibits sp hybridization, and the molecular geometry is linear based on VSEPR theory.

Step 1: Lewis Structure

To determine the Lewis structure for H₂CO, we first need to count the total valence electrons for all atoms in the molecule. For each hydrogen atom, there is 1 valence electron (since hydrogen is in group 1), and for oxygen, there are 6 (since oxygen is in group 16). Carbon, as the central atom, has 4 valence electrons (it's in group 14). The total valence electrons are therefore: 1 (H) × 2 + 6 (O) + 4 (C) = 12 valence electrons Now we need to distribute these electrons around the atoms properly, forming covalent bonds while satisfying the octet rule (excluding hydrogen, which can only have 2 electrons). This results in the following structure: H - C = O In this structure, hydrogen has 1 bond (2 electrons around it), carbon has a single bond with hydrogen and a double bond with oxygen, while the oxygen atom has 1 double bond (4 shared electrons) and 2 lone pairs (4 electrons), totaling 8 electrons.

Step 2: Hybridization of Carbon Atom

Now that we have the correct Lewis structure, we can determine the hybridization of the central carbon atom. To do this, we need to count the electron-occupied regions around the carbon atom. In H₂CO, there are 2 regions: one single bond and one double bond. We need 2 orbitals to accommodate these regions, so one s-orbital and two p-orbitals are required. These will combine to form 2 sp hybrid orbitals on the carbon atom.

Step 3: Molecular Geometry

To identify the molecular geometry for this molecule, we can use the valence shell electron pair repulsion (VSEPR) theory to predict the shape based on the electron-occupied regions surrounding the central carbon atom. In this case, there are 2 regions: one single bond and one double bond. According to VSEPR theory, when there are two electron-occupied regions, the molecule will have a linear geometry due to the repulsion between these regions. In conclusion, using the localized electron model, we have identified the bonding in H₂CO by determining the Lewis structure, hybridization of the central carbon atom, and molecular geometry based on the VSEPR theory. The carbon atom is sp-hybridized and forms a linear geometry with its bonding partners.