# Coordination Numbers and Hybridization schemes of anions

Draw the molecular structures of

(a) the borax anion, $\ce{[B4O5(OH)4]^2-}$

(b) the peroxoborate anion, $\ce{[B2(O2)2(OH)4]^2-}$

          borax                    peroxoborate


(i) What are the co-ordination numbers of the $\ce{B}$ and $\ce{O}$ atoms in the anions (a) and (b)

(ii) What are the hybridisation schemes used by the $\ce{B}$ and $\ce{O}$ atoms in the anions (a) and (b)

I: For (a) $\ce{B}$ has 2 four-coordinate ($\ce{BO4}$) and 2 three- coordinate atoms ($\ce{BO3}$).I'm assuming $\ce{O}$ is 0 since its not a central atom. , (b) $\ce{B} = 4$ and again I'm not sure but I thought coordination numbers only applied to one atom in a molecule. In this case the boron atom.

II: For (a) $\ce{B}$ has 2 $sp^3$ hybrid orbitals and 2 $sp^2$ hybrid orbitals, $\ce{O}$ has just $sp$ orbitals. , (b) $\ce{B}=$ has just $sp^3$ orbitals and $\ce{O}$ has $sp$ orbitals.

I would just like some clarification on the coordination numbers of the $\ce{O}$ atoms in both anions and to see if my hybridisation schemes are correct.