Intermolecular Forces and the States of Matter

Intermolecular Forces and the States of Matter

Solids: The particles of a solid have fixed positions and exhibit motions of vibration.

Liquids: The particles of a liquid are free to move within the confines of the liquid.

Gas: The particles of a gas are far apart and move randomly and rapidly.


Condensation: The process by which a gas becomes a liquid.

Freezing: The process by which a liquid becomes a solid. This occurs at the freezing point which is the same as the melting point.

Sublimation: When a solid changes directly from the solid to the gaseous state.


Hydrogen Bonds: When a hydrogen atom is covalently bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine (N,O,F), it can exhibit an additional polar attraction called a hydrogen bond.


Solution: intimate, homogeneous mixture of two or more substances.

Solute: substance which is dispersed in a solution.

Solvent: substance doing the dissolving, usually present in greatest quantity.

Chemical Sentences: Equations

Chemical equations represent the sentences in the language of chemistry. They are the means of communicating a chemical change using the symbols and formulas to represent the elements and compounds involved in a chemical reaction.


Reactants are the species present before the reaction.

Products are the species present after the reaction.

Reactants → Products

The arrow (→) means “yield(s)” or “react(s) to produce.”


The following are used to denote the states of matter of a species in an equation:

(s) = solid

(l) = liquid

(g) = gas

(aq) = aqueous solution


Coefficients are numbers used to balance a chemical equation. Never change the subscripts.

Volume Relationships in Chemical Equations

Law of Combined Volumes: When all measurements are made at the same temperature and pressure, the volumes of gaseous reactants and products are in a small whole-number ratio.

Volume Relationships in Chemical Equations

Avogadro’s Hypothesis: Volumes of all gases, when measured at the same temperature and pressure, contain the same number of molecules.

Avogadro’s Number

Avogadro’s number is defined as the number of atoms in a 12-g sample of carbon-12 and is:

6.02 x 1023

The Mole

A mole (mol) is defined as the amount of a substance that contains 6.02 x 1023 particles.

The Mole

The Mole

Formula mass is the average mass of a formula unit relative to that of a carbon-12 atom.

It is simply the sum of the atomic masses for all atoms in a formula.

If the formula represents a molecule, often the term molecular mass is used.

The Mole

Molar Volume of a Gas: One mole of any gas occupies a volume of 22.4 L at standard temperature and pressure (STP).

STP is defined as 1 atmosphere (atm) of pressure and a temperature of 0 oC.

Mole and Mass Relationships in Chemical Equations

Stoichiometry involves the quantitative relationship between reactants and products in a balanced chemical equation.

The coefficients of a balanced chemical equation represent moles.


2 H2 + O2 2 H2O

This equation can be read as follows:

2 mol of H2 reacts with one mol O2 to yield

2 mol of H2O.


Steps in a Stoichiometric Calculation:1. Write and balance the chemical equation for

the reaction.2. Determine molar masses of substances

involved in the calculation.3. Use the coefficients of the balanced equation

to convert the moles of the given substance to the moles of the desired substance.

4. Use the molar mass to convert the moles of the desired substance to grams of the desired substance.


The Gas LawsKinetic Molecular Theory of a Gas

Postulates:The particles of a gas are in rapid constant motion.1. The particles of a gas are tiny compared to the

distance between them.2. There is little attraction between the particles of a

gas.3. Collisions between gas molecules are perfectly

elastic.4. Temperature is a measure of the average kinetic

energy of gas molecules.

Solutions

The amount of solute in a given amount of solvent is defined as solution concentration.

A dilute solution contains relative small amounts of solute in a given amount of solvent.

A concentrated solution contains relatively large amounts of solute in a given amount of solvent.

Solutions

Molarity (M) is defined as the moles of solute per liter of solution.

M =liter

mol

Solutions

Percent Concentration

Percent by volume = x 100 solution of volume

solute of volume

Solutions

Percent Concentration

Percent by mass = x 100solution of mass

solute of mass

Acids and Bases: Experimental Definitions

Acids:

taste sour

turn litmus red

react with active metals to release hydrogen gas

react with bases to form water and a salt


Bases:

taste bitter

turn litmus blue

feel slippery

react with acids to form water and a salt


Acids, Bases, and Salts

Arrhenius Theory

Acid: a molecular substance that ionizes in aqueous solution to form hydrogen ions (H+)


Arrhenius Theory

Base: a substance that produces hydroxide ions (OH-) in aqueous solution


Neutralization: When an acid reacts with a base, the properties of each are neutralized and the products are water and a salt.

Acid + Base → Water + Salt

Strong and Weak Acids and Bases

Strong acids ionize completely in water solution. 100%

HCl(aq) → H+(aq) + Cl-(aq)

Weak acids only partially ionize in water solution.

HCN(aq) ↔ H+(aq) + CN-(aq)

Strong and Weak Acids and Bases

Strong bases ionize completely in water solution. 100%

NaOH(aq) → Na+(aq) + OH-(aq)

Weak bases only partially ionize in water solution.

NH3(aq) + H2O ↔ NH4+(aq) + OH-(aq)

Neutralization

During neutralization, an acid reacts with a base, forming water and a salt.

The pH Scale

pH is a means of expressing the acidity or basicity of a solution.

The pH Scale

Electrochemical Cells and Batteries

Electrodes: Pieces of metal where electrons are transferred.

Anode: Electrode where oxidation occurs.

Cathode: Electrode where reduction occurs.


The oxidation and reduction reactions can be represented as half-reactions:

oxidation: Cu(s) → Cu2+(aq) + 2 e-

reduction: 2 Ag+(aq) + 2 e- → 2 Ag(s)

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Overall reaction: Cu(s) + 2 Ag+(aq) → Cu2+(aq) + 2 Ag(s)


Dry Cell:

Zn + 2 MnO2 + H2O → Zn2+ + Mn2O3 + 2 OH-


Lead Storage Batteries:

Discharge:

Pb + PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O

Recharge:

2 PbSO4 + 2 H2O → Pb + PbO2 + 2 H2SO4


Nickel-cadmium batteries are used in portable radios and cordless appliances. They use cadmium anodes and nickel-oxide cathodes.

Fuel cells are an interesting kind of battery. The fuel is oxidized at the anode and O2 is reduced at the anode. The electrons are allowed to flow through a wire and do work.

Corrosion

Silver TarnishSilver tarnish is the result of the oxide on the silver surface reacting with hydrogen sulfide (H2S) in air. This leaves a black film of silver sulfide (Ag2S).Polishing the tarnished silver will restore the shine but at the expense of some of the silver metal. An alternate is to allow aluminum to reduce the silver in the presence of a solution of sodium bicarbonate electrolyte.

Oxygen: An Abundant and Essential Oxidizing Agent

Oxygen is the most common oxidizing agent. It comprises 20% of air and about 50% of the Earth by mass. In the atmosphere, it can exist as oxygen molecules (O2) or ozone (O3). It reacts with metals and nonmetals, forming oxides.

Oxygen: An Abundant and Essential Oxidizing Agent

Ozone (O3) is a powerful oxidizing agent. In the lower atmosphere, it is harmful to both plants and animals. However, in the stratosphere, it serves to protect life on Earth from harmful ultraviolet radiation.

Other Common Oxidizing Agents

Hydrogen peroxide (H2O2) is a common oxidizing agent used as a disinfectant or to bleach hair.

Other Common Oxidizing Agents

Potassium dichromate (K2Cr2O7) will oxidize alcohols and turns green when reduced to chromium (III). It is used in Breathalyzers.

Benzyl peroxide is an antiseptic and used to treat acne.

Chlorine is used as a disinfectant in the treatment of drinking and wastewater.

Bleaches (NaOCl, Ca(OCl2)) are oxidizing agents used on fabrics.

Oxidation, Reduction, and Living Things

Oxidation and reduction reactions are critical to life on Earth. Energy is obtained from food by oxidizing the food. One example is the oxidation of glucose:

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

The reactions of photosynthesis are a series of reductions that are the reverse of the above reaction.

6 CO2 + 6 H2O + energy → C6H12O6 + 6 O2

Oxidation, Reduction, and Living Things

Photosynthesis is the only process that produces the elemental oxygen that is essential for animals on Earth.

Organic Chemistry

Organic chemistry is defined as the chemistry of carbon compounds. Of tens of millions of known chemical compounds, over 95% are compounds of carbon.

The Unique Carbon Atom

Carbon is unique in that carbon atoms can bond to each other to form long chains and rings.

Hydrocarbons

Hydrocarbons are the simplest organic compounds. As their name implies, they are composed entirely of carbon and hydrogen.

Alkanes

Alkanes are hydrocarbons that contain only single bonds. Because all carbon-to-carbon bonds are single bonds, alkanes are often called saturated hydrocarbons.

The simplest hydrocarbon is methane (CH4).

Alkanes

Cyclic Hydrocarbons

The names of cyclic hydrocarbons begin with the prefix cyclo- followed by the name of the alkane with the same number of carbon atoms.

Unsaturated Hydrocarbons

Alkenes are hydrocarbons which contain a carbon-to-carbon double bond. Their general formulas are CnH2n. Their names begin with a prefix denoting the number of carbon atoms followed by the suffix –ene.

Ethylene is the simplest alkene.


Alkynes are hydrocarbons which contain a carbon-to-carbon triple bond. Their general formulas are CnH2n-2. Their names begin with a prefix denoting the number of carbon atoms followed by the suffix –yne.

Ethyne (acetylene) is the simplest alkyne.


Both alkenes and alkynes are unsaturated hydrocarbons. A saturated hydrocarbon has the maximum number of hydrogen atoms attached to each carbon and no double or triple bonds. Unsaturated hydrocarbons can undergo an addition reaction:

Toxicity of Alcohols

All alcohols are toxic. Methanol for instance is oxidized to formaldehyde by liver enzymes. It can lead to blindness and death.

Even ethanol is toxic. The effects of drinking ethanol are due to its toxicity. Drunk driving, alcoholism, and fetal alcohol syndrome are all effects due to the toxicity of ethanol.

Aldehydes and Ketones

Aldehydes and ketones are two families of organic compounds that contain the carbonyl (C=O) functional group.

Carboxylic Acids

Organic acids contain the carboxyl (COOH) functional group.

Esters

Esters generally have a pleasant odor.

Amines and Amides

Amines are derivatives of ammonia. When one or more hydrogen of ammonia is replaced by an alkyl group, an amine is the result. Like ammonia, amines tend to be basic and have similar odors.

Alkaloids

Alkaloids are amines that occur naturally in plants. Many have physiological effects. Morphine, caffeine, nicotine, and cocaine are alkaloids. So are the bases pyrimidine and purine.

Spaceship Earth: Materials Manifest

The Earth is divided into three main regions:

The core is largely iron and nickel and is not accessible.

The mantle consists of silicates and a variety of metals.

The crust is the outer shell of the Earth. The lithosphere is the land masses, the hydrosphere makes up the water, and the atmosphere is the air surrounding the Earth.



The Lithosphere: Organic and Inorganic

The lithosphere is composed of rocks and minerals.

Silicates and the Shapes of Things

The term asbestos applies to a variety of fibrous silicates. The best known is chrysotile, which is a magnesium silicate.

Modified Silicates: Ceramics, Glass, and Cement

Ceramics are clays (aluminum silicates) that have been shaped and fired to a hard, durable material. Ceramic research has led to some amazing new materials.

Modified Silicates: Ceramics, Glass, and Cement

Glass is a noncrystalline solid. It was first made in ancient Egypt by heating sand, sodium carbonate (Na2CO3), and limestone (CaCO3).

The properties of glass can be varied by adding or replacing certain components.

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Intermolecular Forces and the States of Matter