91Ó°ÊÓ

Where in the periodic table are the most electronegative elements found, and where are the least electronegative elements found?

Ammonia, \(\mathrm{NH}_{3}\), and phosphorus trihydride, \(\mathrm{PH}_{3}\), both have trigonal pyramid geometry. Which one is more polar? Explain.

Water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) is more polar than hydrogen sulfide \(\left(\mathrm{H}_{2} \mathrm{~S}\right)\). Explain.

Acetone, a common solvent used in some nail polish removers, has the molecular formula \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\) and contains a carbon- oxygen double bond. (a) Propose two Lewis structures for acetone. (b) What is the geometry around the carbon atoms in each of the structures? (c) Which of the bonds in each structure are polar?

The phosphonium ion, \(\mathrm{PH}_{4}^{+}\), is formed by reaction of phosphine, \(\mathrm{PH}_{3}\), with an acid. (a) Draw the Lewis structure of the phosphonium ion. (b) Predict its molecular geometry. (c) Describe how a fourth hydrogen can be added to \(\mathrm{PH}_{3}\) (d) Explain why the ion has a +1 charge.

The sulfite ion \(\left(\mathrm{SO}_{3}^{2-}\right)\) and sulfur trioxide \(\left(\mathrm{SO}_{3}\right)\) have the same chemical formulas but different molecular geometries. Draw the Lewis dot structures and identify the molecular geometry of each.