Question

Determine the shape around each central atom of the following molecule and identify any deviation from ideal bond angles: CH3−O-CH2CH3
a. H2PO4(no H---P bond)
b. CH3---O---CH2CH3

Answer 1

Answer:

(a) Tetrahedral;

(b) Bent

Explanation:

(a) I assume you meant either $H_2PO_4^-$ or $H_3PO_4$. 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 $109.5^o$.

(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 $104.5^o$. The angle is significantly reduced compared to the tetrahedal arrangement due to the presence of lone pairs that repel stronger than the shared electrons.