Answer:
(a) Tetrahedral;
(b) Bent
Explanation:
(a) I assume you meant either [tex]H_2PO_4^-[/tex] or [tex]H_3PO_4[/tex]. In both cases, we expect to have the same shape, however.
In phosphoric acid, the central atom, phosphorus, has a total of three single P-O bonds and one double P=O bond. No lone pairs are present. According to the VSEPR theory, the steric number is the sum of the bonds (ignoring multiplicity) and the lone pairs present on the central atom. For a total of 4 bonds and no lone pairs, the steric number of P is 4. This corresponds to a tetrahedral shape both electronically and geometrically. We don't expect any significant deviation, as no lone pairs are present on P, so we would have an angle of about [tex]109.5^o[/tex].
(b) In the given ether, oxygen has two bonds. This leaves 2 lone pairs, so that we have an octet on oxygen. Similarly to (a), the steric number is 4. However, we have two lone pairs. This means we don't have a tetrahedral shape anymore, the molecule is bent with an angle of about [tex]104.5^o[/tex]. The angle is significantly reduced compared to the tetrahedal arrangement due to the presence of lone pairs that repel stronger than the shared electrons.
