The bond lengths of iodine in its ground state and excited state differ due to variations in electron configuration and molecular orbital occupancy.
In the ground state, iodine (I2) molecules exhibit a stable bond length typically around 2.66 Å. This bond length is a result of the balance between the attractive forces of the electrons and the repulsive forces between the nuclei and other electron pairs. In this state, the electrons are located in their lowest energy orbitals, leading to a stable configuration.
When iodine absorbs energy, it can be excited to a higher energy state. In this excited state, one or more electrons are promoted to higher orbitals. This change in electronic configuration leads to a weaker effective nuclear attraction, causing the bond length to increase. The excited state of iodine may involve electron configurations that occupy antibonding molecular orbitals or result in electron-electron repulsions that stretch the bond.
As a result, the excited state of iodine typically has a longer bond length compared to its ground state. The shift can be attributed to the interplay of energy levels and the distribution of electrons in the available orbitals, highlighting the intrinsic relationship between electronic states and molecular geometry.