To determine the electron configurations for the beryllium dimer (Be2), its cation (Be2⁺), and its anion (Be2⁻), we first need to understand the molecular orbital energy levels of the beryllium molecule.
In the case of beryllium, each beryllium atom has an atomic number of 4, resulting in the electron configuration of 1s2 2s2. When two beryllium atoms come together to form the Be2 molecule, their atomic orbitals combine to form molecular orbitals. For homonuclear diatomic molecules such as Be2, the bonding molecular orbitals are filled before the antibonding molecular orbitals.
The molecular orbital energy diagram for Be2 looks as follows:
- σ(1s)2 – Bonding orbital
- σ*(1s)0 – Antibonding orbital
- σ(2s)2 – Bonding orbital
- σ*(2s)0 – Antibonding orbital
- σ(2px)0 – Bonding orbital
- σ*(2px)0 – Antibonding orbital
For the neutral Be2 molecule, we have a total of 4 valence electrons (2 from each Be atom). Thus, the electron configuration for Be2 is:
σ(1s)2 σ*(1s)0 σ(2s)2 σ*(2s)0
Now, for Be2⁺, we remove one electron from the total. The first electron removed will typically come from the highest energy orbital, which in this case is the σ(2s) bonding orbital. Therefore, the electron configuration for Be2⁺ is:
σ(1s)2 σ*(1s)0 σ(2s)1 σ*(2s)0
Next, for Be2⁻, we add an electron to the next available orbital, which follows the Aufbau principle. Since we already filled the σ(2s) orbital, the additional electron goes into the σ*(2s) antibonding orbital. Thus, the electron configuration for Be2⁻ is:
σ(1s)2 σ*(1s)0 σ(2s)2 σ*(2s)1
In summary:
- Be2:
σ(1s)2 σ*(1s)0 σ(2s)2 σ*(2s)0 - Be2⁺:
σ(1s)2 σ*(1s)0 σ(2s)1 σ*(2s)0 - Be2⁻:
σ(1s)2 σ*(1s)0 σ(2s)2 σ*(2s)1