Q4. Predict the shapes of BrF5 and SF4.
BrF5: ½(7 + 5) = 6 pairs, 5 bonding and 1 lone: square pyramidal. SF4: ½(6 + 4) = 5 pairs, 4 bonding and 1 lone (equatorial): see-saw.
Q5. Predict the shapes of CO2 and SO2. Why do they differ?
CO2: C has two double bonds (two super pairs) and no lone pair: linear. SO2: S has two bonding super pairs and one lone pair (½(6 + 0) = 3 pairs): bent, about 119.5°. The lone pair on sulphur makes the difference.
Q6. Predict the shapes of H3O+ and ICl4−.
H3O+: ½(6 + 3 − 1) = 4 pairs, 3 bonding and 1 lone: trigonal pyramidal, like NH3. ICl4−: ½(7 + 4 + 1) = 6 pairs, 4 bonding and 2 lone: square planar, like XeF4.
Q7. What is a “super pair”? Give one example of its use.
For VSEPR, the two or three electron pairs of a multiple bond are treated together as a single pair, a super pair, because they point the same way. In CO2 each C=O double bond counts as one pair, so carbon has 2 pairs and the molecule is linear.