Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2021 / Paper 1 / 2 / a / v

No ordinary covalent bond is expected. He's filled 1s orbital is very low in energy, whereas Be supplies another filled shell and much higher empty valence orbitals. Mixing the two occupied s combinations gives no net elementary bond-order gain, and their large energy mismatch limits useful shared covalent character. A very weak dispersion-bound encounter is a different possibility; the answer concerns a conventional covalent bond.