Arrange the species O2, O2^+, O2^-, and O2^2- in order of increasing O-O bond length.
Weakest: O2^2-, O2^-, O2, O2^+, O2^2+ :strongest
To arrange the species O2, O2^+, O2^-, and O2^2- in order of increasing O-O bond length, you need to consider their electronic configurations and the effect of the additional electrons or removal of electrons on the bond length.
Let's start with O2, which is a neutral oxygen molecule. It has a ground state electronic configuration of 1s^2 2s^2 2p^4, with a total of 16 electrons. In this case, there are two bonding molecular orbitals (pi bonds) formed by the overlap of the 2p orbitals of each oxygen atom. The O-O bond length in O2 is around 121 pm.
Next, let's consider O2^+. When an electron is removed from O2, it becomes O2^+. The electronic configuration for O2^+ is 1s^2 2s^2 2p^3. The removal of an electron reduces the electron-electron repulsion, resulting in a shorter O-O bond length compared to O2. Therefore, the O2^+ ion has a shorter O-O bond length than O2.
Now, let's move on to O2^-. When an additional electron is added to O2, it becomes O2^-. The electronic configuration for O2^- is 1s^2 2s^2 2p^5. The addition of an extra electron increases the electron-electron repulsion, causing a longer O-O bond length compared to O2. Thus, O2^- will have a longer O-O bond length than O2.
Finally, let's consider O2^2-. When two additional electrons are added to O2, it becomes O2^2-. The electronic configuration for O2^2- is 1s^2 2s^2 2p^6. The additional electrons will further increase electron-electron repulsion, resulting in a longer O-O bond length compared to O2^-. Thus, O2^2- will have the longest O-O bond length among all the species mentioned.
Therefore, the correct order of increasing O-O bond length is: O2^+ < O2 < O2^- < O2^2-.