Samples: Free-Response Questions
- Explain each of the following in terms of (1) inter- and intra-atomic or molecular forces
and (2) structure.
(a) ICl has a boiling point of 97°C, whereas NaCl has a boiling point of 1400°C.
(b) KI(s) is very soluble in water, whereas I 2 (s) has a solubility of only 0.03 gram per
100 grams of water.
(c) Solid Ag conducts an electric current, whereas solid AgNO 3 does not.
(d) PCl 3 has a measurable dipole moment, whereas PCl 5 does not.Answer
The bullet format will work well here.
- Restatement: Explain each of the following:
(a) ICl has a significantly lower B.P. than NaC1.- ICl is a covalently bonded, molecular solid; NaCl is an ionic solid.
- There are dipole forces between ICl molecules but electrostatic forces between
Na+and Cl–ions. - Dipole forces in ICl are much weaker than the ionic bonds in NaCl.
- I and Cl are similar in electronegativity — generates only partial δ+and δ–around
molecule. - Na and Cl differ greatly in electronegativity — greater electrostatic force.
- When heated slightly, ICl boils because energy supplied (heat) overcomes weak
dipole forces.
(b) KI is water soluble; I 2 is not.
- KI is an ionic solid, held together by ionic bonds.
•I 2 is a molecular solid, held together by covalent bonds. - KI dissociates into K+and I–ions.
•I 2 slightly dissolves in water, maintaining its covalent bond. - Solubility rule: Like dissolves like. H 2 O is polar; KI is polar; I 2 is not polar.
(c) Ag conducts; AgNO 3 does not. - Ag is a metal.
- AgNO 3 is an ionic solid.
- Ag structure consists of Ag+cations surrounded by mobile or “free” electrons.
- AgNO 3 structure consists of Ag+cations electrostatically attracted to NO 3 - poly-
atomic anions — no free or mobile electrons.
Part II: Specific Topics