Please see the attached file.

1. How many sigma (σ) and pi (π) bonds are in each of the following molecules?

Molecule Number of σ bonds Number of π bonds Molecule Number of σ bonds Number of π bonds
CO2 2 2 XeF3+ 3 0
N2 1 2 Cl2CO 3 1
CO32- ion 3 1 BrO3_ 3 2

2. An iron atom is located in a molecule called an "iron-porphyrin" (or "heme") which has an important role for the function of hemoglobin in the blood. The iron atom in hemoglobin is the place where the oxygen molecule (O2) is carried and taken to all the cells in our bodies for cellular metabolism. Before the oxygen gas bonds to the iron, the iron atom has a particular geometry of bonding domains: four nitrogen atoms from the porphyrin molecule are bonded to the iron atom and a fifth nitrogen atom from the hemoglobin molecule is also bonded to the iron. When the oxygen gas molecule bonds to the iron, it forms the sixth bonding domain to iron.

(a) What is the likely hybridization of the bonds around the central iron atom before the oxygen gas molecule bonds to the iron? Explain your answer in one or two sentences.

You would guess sp3d hybridization, since there is only need for 5 ligand bonds (4 from the porphyrin, one from the imidazole (protein)). One from the s, three from the p and one from the d

(b) What is the likely hybridization of the bonds around the central iron atom after the oxygen gas molecule bonds to the iron? Explain your answer in one or two sentences.
After a sixth ligand bond is added, one would consider classifying as sp3d2 in order to fit the six ligands one from the s, three from the p and two from the d.

(c) Some years ago scientists obtained experimental data that appeared to indicate that the geometry around the iron atom in a porphyrin might be the same before and after bonding of the oxygen gas. Because of this data, some scientists argued that a water molecule might be attached to the iron atom and then is displaced by the oxygen molecule. If this was true, what would you predict the geometry to be around the iron atom in the porphyrin? Explain in one or two sentences how this evidence might affect what you answered above.

When looking at the shape of the molecule, specifically around the Fe atom inside the porphyrin ring, there is very little option for the iron to be the central metal in a trigonal bipyrimidal shape. The porphyrin, will be a "tetradentate" ligand, meaning it will bite into the central Fe atom from the four pyrrole nitrogen atoms of the porphyrin, which are from four different directions (like NESW from a compass), as in a square planar complex. The fifth position, (imidazole from the hemoglobin protein) is from the bottom of the square planar. This configuration really is strained, and unless a sixth ligand adds on top (as in an octahedral configuration) this shape would not be preferred.

Good Luck