CHM 031 CHAPTER 11 Outline.docx - CHM 031 CHAPTER 11:...

CHM 031 CHAPTER 11: Solutions Properties and Behaviors Brian Lucas
1. INTERACTIONS BETWEEN IONS: Given that life in air and water depends on
relatively narrow ranges of amounts of solutes dissolved in fluids, the concentration of
solute in a solution can be of critical importance.
a. Solubility is an important feature of many substances in the nonliving world as
well, where the behavior and interactions of substances often depend on the
identity and concentration of solute dissolved in a solvent.
i. Solutions differ from pure substances in several important respects:
1. Solutions and pure liquids behave differently because of the
intermolecular forces between solvent and solute particles.
b. Ion-ion interaction is the strongest kind of interactive force between particles; the
interaction between ions of opposite charge results in the formation of ionic
bonds.
i. The strengths of ion-ion interactions are defined by coulombic interaction .
ii. The corresponding electrostatic potential energy, E , between two
particles with charges
Q
1
and
Q
2
, separated by a distance
d
, is
defined by a relationship we have seen before:
E ∝
Q
1
Q
2
d
1. The value of
E
in the equation is negative when Q both have
opposite signs, which means E is negative for any salt because
the dominant interaction is between cations and anions.
2. Oppositely charged ions attract each other to form an arrangement
characterized by a lower potential energy than the potential energy
of the separated ions.
3. When the ions are far apart, the d term in the equation is large and
E
is a small negative number, with corresponds to lower
energy.
c. The strength of ion-ion interactions means that ionic compounds are most likely
to be solids at room temperature. Whenever cations and anions in the gas phase
combine to make a solid ionic compound, energy is released and the process is
exothermic.
i. The same amount of energy must be absorbed to separate the compound
into its cations and anions.
ii. The inter-ion distance d for ionic compounds is the sum of the ionic radii.
1. The sizes of atoms and ions are a periodic property.
2. Ions in a group of the periodic table, having the same charge,
increase in size as you move down the group.
2. ENERGY CHANGES DURING FORMATION AND DISSOLUTION OF IONIC
COMPOUNDS:
a. The ions must be separated from one another, a process that requires energy to
break the ion-ion interactions that hold the particles in the crystal lattice (
∆ H
ion − ion
).
b. The solvent molecules must also be separated from one another so they can bind
to the ions; this process requires energy to break the dipole-dipole interactions—

CHM 031 CHAPTER 11: Solutions Properties and Behaviors Brian Lucas
in water, these are hydrogen bonds—between solvent molecules (
∆ H
dipole − dipole
).