Outline Chapter 11 Crystals, Ions, and Solutions. 11-1. Ionic and Covalent Crystals 11-2. The Metallic Bond 11-3. Molecular Crystals 11-4. Solubility 11-5. Polar and Nonpolar Liquids 11-6. Ions in Solution 11-7. Evidence for Dissociation. 11-1. Ionic and Covalent Crystals.
11-1. Ionic and Covalent Crystals
11-2. The Metallic Bond
11-3. Molecular Crystals
11-5. Polar and Nonpolar Liquids
11-6. Ions in Solution
11-7. Evidence for Dissociation
Most solids are crystalline, meaning the particles that compose them are arranged in repeated patterns. Amorphous solids have particles irregularly arranged. Crystalline solids fall into four classes:
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.
Covalent crystals are formed when pairs of electrons are shared between adjacent atoms. Some crystals are neither wholly ionic nor wholly covalent but contain bonds of mixed character.
Pictures to the left and below are of diamonds made from graphite. Dr. Hall made diamonds from peanut butter as well.
The metallic bond is formed by a "gas" of electrons that moves freely through the assembly of metal ions that form a solid metal.The metallic bond accounts for the characteristics of metals.
M M M M M M M M
M M M M M M M M
M M M M M M M M
M M M M M M M M
M M M M M M M M
The Electron Sea is responsible for the shiny surfaces of metals.
Some liquids and solids are formed through the action of van der Waals forces, named after the Dutch physicist Johannes van der Waals.
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.
The water molecules in a snowflake are held together by van der Waals bonds. Ice is less dense than its liquid and thus floats.
Cling film owes its properties to polar molecules on its surface.
Non-polar-non-polar interaction occurs between non-polar 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.
Examples of these weak temperary interactions is nitrogen gas. Nitrogen gas is normally non-polar but if the temperature is low enough, these non-polar molecules can form a liquid, liquid nitrogen.
In a solution, the substance present in larger amount is the solvent; the other is the solute. The concentration of a solution is the amount of solute in a given amount of solvent. 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. Examples of solutions:
liquid in liquid-
solid in liquid-
gas in liquid-
gas in gas-
solid in solid-
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.
Lab 16 A
Lab 16 B
Lab 16 C
The solubilities of solids increase with increasing temperatures, while the solubilities of gases in liquids decrease with increasing temperatures. The boiling point of a solution is usually higher than that of the pure solvent, and its freezing point is lower.
Antifreeze lowers the freezing point of your radiator fluid and raises the boiling point.
Salting roads melts the ice.
Making Ice Cream
You must add salt so as to lower the freezing point of the ice water cold enough to freeze the ice cream.
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.
Polar liquids dissolve only ionic and polar covalent compounds. Nonpolar liquids dissolve only nonpolar covalent compounds.
Soaps and Detergents have polar head and a non-polar tail. The tail is attracted to the non-polar greasy dirt and the polar head is attracted to the polar water molecules.
Dissociation refers to the separation of a compound into ions when it dissolves.
Electrolytes are substances that dissociate into ions when dissolved in water; nonelectrolytes are soluble covalent compounds that do not dissociate in solution. Electrolytes in solution are able to conduct electric current.
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. The properties of a solution of an electrolyte are the sum of the properties of the ions present in the solution.
In 1887, the Swedish chemist Svante Arrhenius proposed that many substances exist as ions in solution. His hypothesis was based 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.
Svante Arrhenius (1859-1927)
This device used the color difference between chromic and dichromate ions to measure the alcohol concentration in a person’s breath.
11-9. Water Pollution
11-11. Strong and Weak Acids11-12. Bases
11-13. The pH Scale
Seawater has an average salt content, or salinity, of 3.5 percent.. "Hard" water is freshwater that contains Ca2+ and Mg2+ ions in solution; "soft" water is free of Ca2+ and Mg2+ ions.
Hard water left a deposit of scale in this pipe.
These household water softeners are ion-exchange resins.
Sources of water pollution include:
1. Industrial pollutants
2. Agricultural fertilizers and pesticides
3. Thermal pollution
The biochemical oxygen demand, or BOD, is the amount of oxygen needed to completely oxidize the organic material in a sample of water.
A municipal waste water treatment plant.
Water pollution from a steel mill. Public anger has forced governments to act against such abuse of the environment. Below fertilizers caused algae raft.
An acid is a hydrogen-containing substance that increases the number of H+ ions present when the substance is dissolved in water. The H+ ions released when an acid dissociates in water combine with water molecules to produce hydronium ions, H3O+.
The water solutions of acids taste sour, and acids change the color of litmus dye from blue to red.
Strong acids dissociate completely; weak acids dissociate only slightly. 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.
A base is a substance that contains hydroxide groups and whose solution in water increases the number of OH- ions present.Strong bases dissociate completely; weak bases dissociate only slightly. The water solutions of bases have a bitter taste, a soapy feel, and turn red litmus to blue.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.
The pH scale expresses the exact degree of acidity or basicity of a solution in terms of its H+ ion concentration. A solution that is neither acidic nor basic is said to be neutral and has a pH of 7. Acidic solutions have pH values of less than 7. Basic solutions have pH values of more than 7.
To find the [H+]from the pH just insert the pH into 10-pH.
For example, if the pH is 4 the [H+] is 10-4.
If the pH is 6 the [H+]is
If the pH is 10 the [H+]is
If the pH is 8 the [H+]is
To find the pH from the [H+]just insert the [H+]into -log [H+].
For example, if the [H+]is 10-4 the pHis
If the [H+]is 10-9 the pH is
If the [H+]is 10-2 the pH is
pH = - log [H+]
[H+] = antilog (-pH) = 10-pH
If [H+] = 2.0 x 10-9 then
pH = -log(2.0 x 10-9) = 8.69897
pH =8.70 [H+] = 10-8.7
If pH = 3.2 then
[H+] = antilog(-3.2) = 6.31 x 10-4
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. In neutralization reactions, H+ and OH- ions join to form water molecules. Ions left in solution as a result of neutralization can combine to form a salt when the solution is evaporated to dryness. Most salts are crystalline solids that consist of positive metal ions and negative nonmetal ions.