Question

As compared with \(\mathrm{CO}\) and \(\mathrm{O}_{2}, \mathrm{CS}\) and \(\mathrm{S}_{2}\) are very unstable molecules. Give an explanation based on the relative abilities of the sulfur and oxygen atoms to form \(\pi\) bonds.

Short answer

The instability of CS and S2 as compared to CO and O2 can be attributed to the differences in the ability of oxygen and sulfur atoms to form π bonds. Oxygen atoms have a greater ability to form strong π bonds due to their unpaired electrons in two half-filled p orbitals and smaller atomic size, which allows for better orbital overlaps and stronger bonding. In contrast, sulfur has fewer unpaired electrons in its p orbitals and a larger atomic size, leading to weaker bonding and instability in molecules like CS and S2.

Step-by-step solution

Electron Configurations of Oxygen and Sulfur

First, we need to recall the electron configurations of oxygen and sulfur. Oxygen, atomic number 8, has an electron configuration of: 1s² 2s² 2p⁴. Sulfur, atomic number 16, has an electron configuration of: 1s² 2s² 2p⁶ 3s² 3p⁴. In both cases, the p orbitals play a crucial role in the formation of π bonds. Oxygen has two half-filled p orbitals remaining, while sulfur has two half-filled and one completely filled p orbitals.

Atomic Orbitals Involved in π Bonds

π bonds are formed through the sideways overlap of p orbitals. Due to the presence of unpaired electrons in the p orbitals, oxygen can form two π bonds (in O2) while sulfur can form only one such π bond (in S2). Therefore, sulfur atoms are less capable of forming strong π bonds compared to oxygen.

Overlap and Bonding Strength

The strength of a π bond is governed by the extent of overlap between atomic orbitals. Since Oxygen is in the second period and Sulfur is in the third period, the size of the oxygen atom is smaller than the sulfur atom, leading to better orbital overlaps and stronger π bonds in oxygen-containing molecules (CO and O2) as compared to sulfur containing molecules (CS and S2).

Conclusion

In summary, the instability of CS and S2 as compared to CO and O2 can be explained by the differences in the formation of π bonds between sulfur and oxygen atoms. Oxygen has a greater ability to form π bonds due to its unpaired electrons and smaller atomic size, which allows for better orbital overlaps and stronger bonding. On the other hand, sulfur has a lower ability to form π bonds due to fewer unpaired electrons and larger atomic size, resulting in weaker bonding and instability of the molecules CS and S2.