Outline Chapter 10 Crystals, Ions, and Solutions
10-1. Ionic and Covalent Crystals
A. Most solids are crystalline, meaning the particles that compose them are
arranged in repeated patterns.
B. Amorphous solids have particles irregularly arranged.
C. Crystalline solids fall into four classes:
1. Ionic
2. Covalent
3. Metallic
4. Molecular
D. Ionic crystals are formed by the attraction between positive and negative
ions.
1. Face-centered cubic ionic crystals have ions located at the
corners and centers of the faces of a series of cubes.
2. Body-centered cubic ionic crystals have each ion located at the
center of a cube at whose corners are ions of the other kind.
E. Covalent crystals are formed when pairs of electrons are shared between
adjacent atoms.
F. Some crystals are neither wholly ionic nor wholly covalent but contain
bonds of mixed character.
10-2. The Metallic Bond
A. The metallic bond is formed by a "gas" of electrons that moves freely
through the assembly of metal ions that form a solid metal.
B. The metallic bond accounts for the characteristics of metals.
10-3. Molecular Crystals
A. Some liquids and solids are formed through the action of van der Waals
forces, named after the Dutch physicist Johannes van der Waals.
B. There are several types of van der Waals interactions:
1. Polar-polar interaction occurs between polar molecules whose
positively and negatively charged ends cause them to line up with the
ends that have opposite charges adjacent.
2. Polar-nonpolar interaction occurs between polar and nonpolar
molecules because the electric field of the polar molecules causes
separations of charge in the nonpolar molecules. The oppositely
charged ends of the polar and nonpolar molecules produce an
attractive force.
3. Nonpolar-nonpolar interaction occurs between nonpolar molecules
when the molecule's electrons at any given moment are distributed
unevenly. This creates temporarily charged molecules whose
adjacent ends having opposite signs results in an attractive force.
C. Van der Waals forces are much weaker than ionic, covalent, and metallic
bonds.
10-4. Solubility
A. In a solution, the substance present in larger amount is the solvent; the
other is the solute.
B. The concentration of a solution is the amount of solute in a given amount
of solvent.
C. The solubility of a substance is the maximum amount that can be
dissolved in a given quantity of a particular solvent at a given temperature.
D. A saturated solution contains the maximum amount of solute possible at
a given temperature; a supersaturated solution contains more dissolved
solute than is normally possible at a given temperature and is usually
unstable.
E. The solubilities of solids increase with increasing temperatures, while the
solubilities of gases in liquids decrease with increasing temperatures.
F. The boiling point of a solution is usually higher than that of the pure
solvent, and its freezing point is lower.
10-5. Polar and Nonpolar Liquids
A. A polar liquid is a substance whose molecules behave as if negatively
charged at one end and positively charged at the other. The molecules of a
nonpolar liquid have uniform charge distributions.
B. Polar liquids dissolve only ionic and polar covalent compounds. Nonpolar
liquids
dissolve only nonpolar covalent compounds.
C. Dissociation refers to the separation of a compound into ions when it
dissolves.
D. Electrolytes are substances that dissociate into ions when dissolved in
water; nonelectrolytes are soluble covalent compounds that do not
dissociate in solution.
E. Electrolytes in solution are able to conduct electric current.
10-6. Ions in Solution
A. Ions in solution have their own sets of properties that differ from their
original atoms and from the original solute. Dissociation is a type of chemical
change.
B. The properties of a solution of an electrolyte are the sum of the properties
of the ions present in the solution.
10-7. Evidence for Dissociation
A. In 1887, the Swedish chemist Svante Arrhenius proposed that many
substances exist as ions in solution.
B. Arrhenius based his hypothesis on two points:
1. Reactions between electrolytes in solution occur almost
instantaneously, but very slowly or not at all if the electrolytes are dry.
2. Electrolyte solutions have lower freezing points than comparable
solutions of nonelectrolytes.
10-8. Water
A. Seawater has an average salt content, or salinity, of 3.5 percent.
B. "Hard" water is freshwater that contains Ca2+ and Mg2+ ions in solution;
"soft" water is free of Ca2+ and Mg2+ ions.
10-9. Water Pollution
A. Sources of water pollution include:
1. Industrial pollutants
2. Agricultural fertilizers and pesticides
3. Thermal pollution
B. The biochemical oxygen demand, or BOD, is the amount of oxygen
needed to completely oxidize the organic material in a sample of water.
10-10. Acids
A. An acid is a hydrogen-containing substance that increases the number of
H+ ions present when the substance is dissolved in water.
B. The H+ ions released when an acid dissociates in water combine with
water molecules to produce hydronium ions, H3O+.
C. The characteristic properties of acids are actually the properties of H3O+
ions rather than the properties of H+ ions.
D. The water solutions of acids taste sour, and acids change the color of
litmus dye from blue to red.
10-11. Strong and Weak Acids
A. Strong acids dissociate completely; weak acids dissociate only slightly.
B. Some substances, such as carbon dioxide, do not contain hydrogen but
produce acidic solutions by reacting with water to liberate H+ ions from water
molecules.
10-12. Bases
A. A base is a substance that contains hydroxide groups and whose solution
in water increases the number of OH- ions present.
B. Strong bases dissociate completely; weak bases dissociate only slightly.
C. Some substances, such as ammonia, do not contain OH but produce
basic solutions because they react with water to release OH- ions from water
molecules.
D. The water solutions of bases have a bitter taste, a soapy feel, and turn
red litmus to blue.
E. The name alkali is sometimes used for a substance that dissolves in
water to give a basic solution. The terms alkaline and basic mean the same.
10-13. The pH Scale
A. Pure water dissociates very slightly into H+ and OH- ions.
1. In an acidic solution, the concentration of H+ ions is greater than in
pure water, and the concentration of OH- ions is lower.
2. In a basic solution, the concentration of OH- ions is greater than in
pure water, and the concentration of H+ ions is lower.
B. The pH scale expresses the exact degree of acidity or basicity of a
solution in terms of its H+ ion concentration.
1. A solution that is neither acidic nor basic is said to be neutral and
has a pH of 7.
2. Acidic solutions have pH values of less than 7.
3. Basic solutions have pH values of more than 7.
C. A change in pH of 1 means a change in H+ ion concentration by a factor
of 10.
10-14. Salts
A. When a basic solution is mixed with an acidic solution, the base destroys,
or neutralizes, the properties of the acid and vice versa. The process is
called neutralization.
B. In neutralization reactions, H+ and OH- ions join to form water molecules.
C. Ions left in solution as a result of neutralization can combine to form a salt
when the solution is evaporated to dryness.
D. Most salts are crystalline solids that consist of positive metal ions and
negative nonmetal ions.