Is the valence for Boron .B: or .?. ? Explain this in terms of the molecular geometry.
The first two valance electrons do generally pair because they go into a s orbital which can hold just two electrons. After the first two, the next few go into p orbitals. For these, the scatter before pair rule (Hund's rule) applies.
The Boron molecule is just the atom, (a molecule of one atom). Consequently, the "molecular" geometry is just a sphere. Boron does has three valence electrons (2 s2 2p ). The electron cloud cannot be exactly spherical due to the occupied p orbital. However, this fact has no chemical significance. For most chemical reactions with Boron, the three valance electrons hybridize to form sigma bonds.