Question

The number of bonds present and the number of unpaired electrons according to valence bond theory in \(\mathrm{O}_{2}\) are (1) 2,2 (2) 2,0 (3) 3,0 (4) 0,2

Short answer

The number of bonds is 2, and the number of unpaired electrons is 2.

Step-by-step solution

Determine the Electron Configuration

Start by writing the electron configurations for oxygen atoms. The electron configuration for an oxygen atom is 1s² 2s² 2p⁴. Oxygen molecules, \(\mathrm{O}_{2}\), have two oxygen atoms each with this configuration.

Apply Valence Bond Theory

According to valence bond theory, combine the atomic orbitals. Each oxygen atom has 2 unpaired electrons in the 2p orbitals.

Form Sigma and Pi Bonds

In \(\mathrm{O}_{2}\), one sigma bond forms from the head-to-head overlap of 2p orbitals, and one pi bond forms from the side-to-side overlap of the two unpaired electrons' 2p orbitals. This accounts for a double bond (one sigma and one pi bond) between the oxygen atoms.

Count Unpaired Electrons

Check the molecular orbitals. \(\mathrm{O}_{2}\) has two unpaired electrons in the \( \pi^* \) antibonding orbitals.

Conclusion

Combine the previous steps: \(\mathrm{O}_{2}\) has a double bond (one sigma bond and one pi bond) and two unpaired electrons.

Key concepts

Electron Configuration

Understanding the electron configuration of oxygen is the first step in applying the valence bond theory to \(\text{O}_2\). For an oxygen atom, the electron configuration is 1s² 2s² 2p⁴. This means oxygen has 8 electrons arranged around its nucleus.

In the 2p orbital, there are 4 electrons: two of these fill ten 2p_x and 2p_y orbitals, while the other two each occupy separate 2p_z orbitals. When describing \( \text{O}_2 \), we consider the electron configuration of two oxygen atoms together. Thus, the molecular \( \text{O}_2 \) configuration lays the groundwork for understanding bonding and unpaired electrons.

Sigma and Pi Bonds

Next, let's explore sigma and pi bonds in \( \text{O}_2 \). According to valence bond theory, bonds form when atomic orbitals overlap. A sigma bond is a strong bond formed by the head-to-head overlap of atomic orbitals. In \( \text{O}_2 \), this happens between the 2p orbitals of two oxygen atoms, forming a stable bond.

A pi bond, on the other hand, forms from the side-to-side overlap of p orbitals. Each oxygen has one unpaired electron remaining, these electrons overlap to form a pi bond. Therefore, \( \text{O}_2 \) has one sigma and one pi bond, giving us a double bond. Sidenote, double bonds are usually stronger and shorter than single bonds because they involve shared electrons more closely holding the atoms together.

Unpaired Electrons

The final important piece to consider is the unpaired electrons in \( \text{O}_2 \). In its ground state, \( \text{O}_2 \) possesses two unpaired electrons. These reside in the antibonding \( \text{π}^* \) molecular orbitals.

These unpaired electrons give \( \text{O}_2 \) interesting magnetic properties, such as its paramagnetism, which means it is attracted to magnetic fields.

Summarizing, molecular oxygen (\text{O}_2) features a double bond comprised of one sigma bond and one pi bond and holds two unpaired electrons in its higher energy orbitals. Understanding these key features allows us to predict the behavior and reactivity of oxygen in various chemical contexts.