INTRODUCTION TO CHEMISTRY

By: Ray Shelton

INTRODUCTION:
Definition of Chemistry:
Chemistry is the science of matter, its properties, composition, structure and the transformations or changes that it undergoes.
Two branches of Chemistry:
(a) Descriptive Chemistry - this is the descriptive phase of the scientific method applied to matter.
(b) Theoretical Chemistry - this is the explanatory phase of the scientific method applied to matter.

The early history of Chemistry:
The early history of Chemistry is the history of descriptive Chemistry. The study of the properties and kinds of matter leads to the classification of matter.
Classification of Matter:
1. The three phases of matter.
  One of the earliest classification of matter is the three phases of matter: solid, liquid, gas. This classification is based on two characteristics of matter: volume and shape.
  1. Solids have definite volume and definite shape. That is,
    they have their own volume and shape independent of their container.
  2. Liquids have definite volume but indefinite shape. That is,
    they have their own volume but take the shape of their container.
  3. Gases have indefinite volume and indefinite shape. That is,
    they take the volume and shape of their container.
2. Early History of the concept of element.
  The modern classification of matter revolves about the concept of element. But the modern concept of element differs from the ancient concept of element. The ancient concept of the element was introduced in the attempt to explain the three phases of matter.
  1. Empedocles (c. 490-435 B.C.) He introduced the concept of element and the four irreducible elements: earth, water, air, fire. He held that all material substances are produced by the union of these Four Elements. He did not believe that they contain atoms.
  2. Aristotle (384-322 B.C.) He defined an element or "simple body" as "one of those bodies into which other bodies can be decomposed and which of itself is not capable of being divided into others." This is similar to the modern definition if there is added "chemically decomposed." He did not distinguish between mechanical mixing and chemical composition; neither did he distinguish between mixtures and compounds. The Four Elements are properties or qualities rather than substances; there was only one substance or prime matter = hule. He believed that the Four Elements were a combination of four basic qualities: wet, cold, hot and dry. For example, fire was the combination of hot and dry. He also held that one element can be changed into another by overcoming these qualities by their opposities. This led to the hope of changing the "base" metals into gold. He also held that there was a fifth element - "quintessence"; the heavenly bodies are made of this celestial (not terrestrial) element.
3. Medieval Chemistry and Alchemy.
  Alchemy was an art that arose in Alexandria between the first and third century A.D. It was based on Greek science and philosophy and combined practical chemical arts with mysticism and magic. The Alexandrian alchemical treatises were translated into Arabic after the Arabian conquest of Egypt in 640 A.D. Great interest in the art developed among Arabian men of learning between 700 and 1200 A.D. To the Four Elements they added the sulphur-mercury theory and clarified the doctrine of the philosopher's stone and the elixir of life. Alchemy was introduced into western Europe in the 12th and 13th century by way of Spain, where Latin translations of Arabian manuscripts were prepared. Western Europe became the principal place of alchemical activity until the art finally died out in the late 18th century.
  The two goals of Alchemy were to find the philosopher's stone and the elixir of life. The search for the philosopher's stone was inspired by the hope of changing the "base" metals, such as iron, copper, etc. into the "noble" metals, such as gold, silver, etc. This expectation was based on the belief in the transmutation of matter, i.e. the transformation of one kind of matter into another, which was implicit in Aristotelian philosophy. If the different kinds of matter differ only in their relative proportions of the Four Elements, then it was logical to suppose that alteration of these proportions will bring about the transmutation. This they believed could be accomplished by a certain substance which became known as the "philosopher's stone". All this seemed perfectly rational within the framework of Aristotle's philosophy. Of course the search for the philosopher's stone failed but many techniques for use in the modern Chemistry were developed. Alexandrian and Arabic manuscripts contain detailed descriptions of such techniques as distillation, filtration, crystallization, sublimation, as well as well as descriptions of many new materials discovered, among them phosphorus, antimony, bismuth, zinc, alcohol, several mineral acids and salts, in the course of the alchemical investigations. Seveal worthwhile attempts were made to extend the classification of matter. For example, Abrabian alchemists formulated the hypothesis that metals are composed of two principles, mercury and sulfur, in addition to the Four Elements.
  The Arabian scholar, ibn-Sina (980-1036), later known as Avicenna, was the first Alchemist to state the belief that the transmutation of the elements was impossible. Avicenna's treatise strongly influenced European Alchemist scholars, including the Dominican priest Abertus Magnus (1193-1280), the teacher of Thomas Aquinas, and the Franciscan Roger Bacon (1214-1292).
4. Early Medical Chemistry.
  Roger Bacon, who remained a strong believer in the transmutation of the elements, thought that alchemical techniques should be applied to medicinals, and only incidentally to gold. This emphasis upon medicine was in line with the other goal of Alchemy, the search for an "elixir" of eternal life. In spite of his emphasis on medicine, Bacon is not considered the founder Medical Chemistry. Theophrastus Bombastus von Hohenbeim (1493-1541), more commonly known as Paracelsus, is considered the founder of Medical Chemistry. Paracelsus' training was medical, and he devoted his life to an attempt to reform the medical profession. In addition to his medical treatises, he wrote tracts concerning the nature of matter. He believed in the transmutation of matter and the Four Elements; to the two Arabic principles of sulfur and mercury he added a third, salt. In Paracelsus' view the Four Elements manifest themselves in the form of these principles, sulfur associated with property of combustibility, mercury with liquidity, and salt with solidity.
  Perhaps the greatest of the medical chemists was the physician Johann Baptista van Helmont (1577-1644) of Brussels. He was the first western scholar to reject the Aristotelian Four Elements; he also rejected Paracelsus' three principles. He held that there were only two primary elements, air and water. Each kind of solid he thought to have a "spirit" in addition to its primary matter. He succeeded in isolating some these "spirits" (vapors), for which he coined our word gas.

The Birth of Modern Chemistry.

Definition of an Element.
The English natural philosopher, Robert Boyle (1627-1691), after whom the gas law is named, in 1661 published a book titled, The Skeptical Chemist, in which he defined an element as "those primitive and simple or perfectly unmingled bodies, which not being made of any other bodies... are the ingredients of which (all other bodies) are immediately compounded." This definition makes a distinction between elements and compounds. However, he gave no prescription for distinguishing elements from other compounds. He vigorously attacks the Aristotelian concept of element and rejects the Four Elements, but gives no list of what he considered to be the elements. He also rejected Paracelsus' three principles and van Helmont's two elements as hypotheses insufficiently grounded in observation.

The Problem of Chemical Change.

The Changes of Matter.
1. Physical Changes:
  Physical changes are those changes of matter which take place without altering the composition of the matter or changing it into some other kind of matter. Physical changes are quantitative changes of matter. Examples: changes of state, pulverizing, stretching, electrification, magnetization. The following are some of the conditions bringing about physical change:
  (1) Temperature and Heat.
  (2) Pressure.
  (3) Force.
  (4) Motion: velocities near the speed of light will change length, time, and the mass of a body.
  (5) Electrification.
  (6) Magnetization.
2. Chemical Changes:
  Chemical change are those changes of matter in which the composition of the matter is altered and the matter is changed into some other kind of matter. Chemical changes are qualitative changes of matter. The materials entering into the chemical change lose their original physical and chemical properties and some new materials with new physical and chemical properties are formed. Chemical changes are called chemical reactions and are expressed by a chemical equation.
  There are four basic kinds of chemical reactions:
  (1) Chemical Composition: several substances combine together to form more complex substances.
  (2) Chemical Decomposition: substances are broken down into simpler substances.
  (3) Chemical Displacement or Replacement: a substance takes the place of another substance in a more complex substance.
  (4) Chemical Double Decompositon or Double Replacement: two substances react to form two new substance by decomposing into simpler substances and recombining the simpler substances into two more complex substances.
Combustion:
Combustion is any chemical change which involves the production of a flame. Examples: burning of paper or wood: wood + heat -> ash Observations:
1. Combustion is a radical transformation of matter.
2. Air essential to combustion.
3. A decrease in volume of air if the combustion is enclosed in a container. Example: a candle mounted in tray of water and when covered by an empty cylinder the flame quickly go out and the water rises in the cylinder.
4. A decrease in weight - the ashy residue is smaller quantitatively in weight compared with original material. After combustion the residue is always strikingly less in size than the original sample.
5. Change cannot be reversed.
Calcination:
Calcination is the alteration of metals upon heating in air; it is a chemical change in which a metal is change into the "calx" of the metal - name given by Alchemist. Example: Red rust is calx of iron.
1. Calcination is a radical transformation of matter. The calx is radically different from the original metal - completely unmetallic properties.
2. Air is essential to calcination.
3. The process can be reversed. The reversed process is called reduction and generally performed by mixing the calx and charcoal together (wood in which nearly all water moisture has been driven out by heating - nearly pure carbon). Sometimes done by heat only.
```
calcination:       metal + heat -> calx
reduction:         calx + charcoal -> metal
reduction by heat: mercury calx + heat -> mercury
```
4. Increase of weight: after calcination the weight of the calx is invariably greater than the original metal sample.

The Phlogiston Theory:
The Phlogiston theory was developed during 18th century to explain the two processes of combustion and calcination.

The theory was suggested by Johann Becher (1635-1682), a German. He extended the ideas of Paracelsus concerning matter. He believed that matter consisted of two elements of air and water and three principles of inflammability, fusibility, "mercurial nature." Parcelsus' principles were sulfur, salt and mercury; Becher's principles placed emphasis upon certain properties or essences of these materials.
The theory was developed and popularized by another German, Georg Ernest Stahl (1660-1734). His Fundamenta Chymiae, published in 1723, was the most influential chemistry text of the early 18th century. He introduced the name phlogiston (from Greek, phlox = "flame") for Becher's "essence of inflammability".
"The word thus represents nothing more than the ancient Aristotliean element fire in a more sophisticated form." (B&P,117)

The Becher-Stahl phlogiston theory contained two basic assumptions:
(1) All combustion and calcination involve the liberation of phlogistion.
(2) Air must be present to absorb the phlogiston and that the capacity of given volume of air for phlogiston was limited.
As developed by Stahl the theory was able to explain satisfactorily a wide vaariety of facts about combustion and calcination.

	Observations	Phlogiston Theory	Oxygen Theory
1.	Candle burns.	Candle gives off phlogiston.	Candle combines with oxygen in air.
2.	Flame goes out in enclosed space.	Air becomes saturated with phlogiston.	Oxygen in enclosed space is used up.
3.	Charcoal leaves little residue when burned.	Charcoal is pure phlogiston.	All charcoal combines with oxygen to form gas carbon dioxide.
4.	Combustible materials lose weight when burned.	Weight loss due to phlogiston given off.	Oxygen combines with carbon to form gas carbon dioxide.
5.	Metals forms calx when heated in air.	Metals are compounds of calx and phlog.	A calx is a compound of metal and oxygen.
6.	Some calxes turn to metal when heated with charcoal.	Phlogiston from charcoal is restored to calx.	Oxygen in calx combines with carbon to form carbon dioxide gas.
7.	Mouse dies in enclosed space.	Mouse saturates air with phlogiston.	Mouse exhausts oxygen in enclosed space.

The Oxygen Theory:
1. Difficulties with the Phlogiston Theory.
  There were two major difficulties with the Phlogiston Theory for which ad hoc assumptions were added to the theory to explain these difficulties.
  (1) The air after the flame goes out in enclosed space has less volume. This is a quantitative difficulty for which the ad hoc assumption that phlogistion shrinks the volume of the air in the enclosed space was introduced to explain the difficulty.
  (2) Metals gain weight on calcination. This is also a quantitative difficulty which was opposite to what the theory predicted for combustion; for example: wood ash weighed less after combustion. To explain this difficulty two kinds of phlogiston were posited: the phlogiston in combustion had positive weight and the phlogiston in calcination had a negative weight. This ad hoc assumption apparently was not widely held and these difficulties were usually ignored. But later they became crucial.
2. Developments leading up to the Oxygen Theory:
  (1) Development of pneumatic chemistry. The development of techniques to manipulate and measure the volume of gases was mainly the work of an English vicar Stephen Hales (1677-1761). He developed the pneumatic trough which was an apparatus to collect gases by displacing the water in an inverted glass container by the gas. Although Hales was mostly interested in the "airs" (he believed that air was an element) expelled by biological systems, he did collect gases given off by heating such materials as coal, saltpeter, etc. But he did not recognize that these were different from air.
  (2) Joseph Black (1728-1799), a Scottish physician and chemist, rediscovered the gas now called carbon dioxide. This gas was originally described by van Helmont which he called the gas sylvestre. Black collected this gas by pneumatic techniques by heating magnesium carbonate which he called magnesia alba. Later he found that this same gas was given off by heating limestone which became quicklime. He observed that this gas is incapable of supporting combustion, is moderately soluble in water, and is completely absorbed by solutions of alkali (that is, sodium hydroxide). Black called this gas "fixed air", since it could be kept, "fixed", in the solid state by limestone. For Black had found that quicklime, the product of heating limestone, was capable of recapturing the gas, thus restoring the limestone. Thus he had discovered a reversible chemical process. This provided him with a simple test for his "fixed air": this gas when passed through limewater (quicklime dissolved in water) would turn the limewater cloudy by the preciptation of the insoluble limestone. With this test he made the important discoveries that this gas was present in respired air and in the air blown over glowing charcoal.
  (3) Henry Cavendish (1731-1810), who later determined the value of the Newtonian Gravitational Constant G in 1798, rediscovered the gas now called hydrogen. This inflammable gas had been known to van Helmont and Boyle. Cavendish prepared this gas, which he called "inflammable air", by the action of acids on several metals, and concluded (incorrectly) from his observations that the gas arose from the metal rather than from the acid. This erroneous conclusion lead to a later form of the phlogiston theory that incorporated the assumption that "inflammable air" is itself phlogiston.
  (4) Joseph Priestley (1733-1804), an English nonconformist clergyman, made in 1774 the most important discovery of 18th century chemistry, that of the gaseous-substance which we now call oxygen. It was independently discovered by Carl Wilhelm Scheele (1742-1786) in Sweden but because he delayed the publication of his findings until 1777, Priestley is given credit for the discovery. Priestley over a long period of time investigated many gases such as ammonia, hydrogen chloride, carbon monoxide, sulfur dioxide, and nitrous and nitric oxide. His work with oxygen which he published in 1774 began with the observation that the red calx of mercury, unlike other calxes then known could be decomposed by heating without charcoal. He observed that this reaction was reversible in a simple way; the red calx was composed when mercury is heated at low temperatures in air and decomposed by heating at it at a higher temperature. Priestley collected the gas evolved and noted that it supported the combustion of the candle flame more brilliantly than ordinary air. At first he thought that this gas was a gas he had previously descovered which he called "dephlogisticated nitrous air" (called today nitrous oxide, or "laughing gas"), but as result of further experiments performed during March 1774, he concluded that it was a new gas. He called it "dephlogisticated air" because its properties were like to those of air, but more intense. He found that mice placed in an enclosed space with this gas could survive much longer than in an equal volume of common air. It seemed to stimulate life processes when it was breathed. To him this was because it was completely devoid of phlogiston, hence capable of absorbing greater quantities of phlogiston given off in combustion. Priestley saw no conflict with the phlogiston theory, which he defended vigorously until the end of his life.
3. The Oxygen Theory:
  The French chemist Antoine Laurent Lavoisier (1743-1794) had formulated as early as 1772 the hypothesis that an "atmospheric principle" is taken up from the atmosphere during combustion and calcination. He was disturbed by the difficulites with the phlogiston theory caused by the discoveries of Black and Cavendish, even though they were not disturbed. Lavoisier's own experiments using the chemical balance led him to form a new theory of combustion and calcination. He had found that tin increased in weight when heated in air, and in the process some of the air had been absorbed. He found that phosphorus also gained weight and the product formed by this heating in air when dissolved in water formed an acid. When he heated lead calx (lead oxide) with charcoal, not only was metallic lead formed but the "fixed air" of Black was formed. In the fall of 1774 Priestly visited Paris and was invited to dine with the Lavoisers. Fresh with his discovery and full of the subject, he related how the red calx of mercury, obtained by gentle heating mercury, had yielded when heated more vigorously not only the mercury but the "dephlogisticated air" with its remarkable properties. According to Priestley, "All the company, and Mr. and Mrs. Lavoisier as much as any, expressed great surprise." Not long after, Lavoisier repeated Priestley's experiment and devised his now famous experiment to prove or disprove that mercury calx was formed by combining with something in the air. A quantity of mercury was heated for twelve days in contact with 50 cubic inches of air. The red calx of mercury was observed to form on the surface of the mercury, and the volume of the air in contact with it slowly contracted to 42 cubic inches, showing that something had been taken from the air. When the contraction appeared to have ceased he carefully removed the red calx from the surface of the mercury in the retort and weigh it. He checked the gas remaining in the bell jar and that a candle was promptly extinguished by it. Then he placed the red calx in another retort and heated to a higher temperature, collecting the gas given off in another bell jar. When the production of gas ceased he found that it had a volume of 8 cubic inches, the same quantity by which the volume of air contracted in the first part of the experiment. He then tested the gas just collected and found that a candle flame burned brightly; it had all the properties of Priestly's "dephlogisticated air". Then he mixed this second gas with the gas that remained from the first part of experiment, observing no chemical change. He found that the mixture could not be distinguished from ordinary air. He concluded that ordinary air was a mixture of two gases, one active in combustion and the other inert. The first he called oxygen (Greek "acid former"), because he believed mistakenly that all acids contained this gas, and second azote ("not living"), which later became known as nitrogen. Thus he showed that ordinary air was not an element, but a mixture of gases. Since no chemical reaction occurred when mixing the gases, the air was not a chemical compound.
  In September, 1775, Lavoiser published a moderate attack on the phlogiston theory, as he put it, "...not to substitute a rigorously demonstrated theory but solely a hypothesis which appears to me more probable, more conformable to the laws of nature, and which appears to me to contain fewer forced explanations and fewer contradictions." In the following years with a flood of publications, he gradually increased the force of his attacks, until in 1781 he was ready to present a fully formulated theory that made the phlogiston hypothesis unnecessay. In that year Lavoiser published his Traite Elementaire de Chimie in which he set forth his oxygen theory of combustion and calcination. This theory was based on two assumptions:
  (1) Air is not an irreducible element but a mixture: approximately one-fifth of air is capable of supporting combustion, calcination, and respiration, and is called oxygen. The other four-fifths, incapable of supporting combustion, consist largely of the gas later called nitrogen. It is now known that a small portion of the air is a mixture of other gases: argon, carbon dioxide, water vapor, neon, helium, krypton, and xenon. Thus when a candle burns in an enclosed space, the combustion continues until the available oxygen in the air is consumed.
  (2) Combustion and calcination are both chemical change involving a combination of some substance with atmospheric oxygen. Many of the substances involved in combustion contain carbon, which combines with oxygen to form the compound carbon dioxide (Black's "fixed air"); this compound escapes into the air, giving the impression that the burning material loses weight. Since charcoal is almost pure carbon, its combustion with oxygen to form carbon dioxide gas leaves no residue.
  Calcination differs from combustion only in that no gas is formed during the combination of the metal with oxygen. The increase in weight during calcination of the metal is due the added weight of the oxygen from the air. Metals are elements, not compounds of calx with phlogiston. Finally, animal respiration involves the inhalation of oxygen and the expiration of carbon dioxide, and thus is a process similar to combustion, but without a flame.
  Lavoisier had heard of Cavendish's experiments with "inflammable air", especially the burning of it in air to produce water. He repeated the experiments and concluded that water must be a compound of the "inflammable air" and oxygen and not an element as so long believed. He renamed Cavendish' "inflammable air" hydrogen (Greek "water former"). Not only was the 18th century phlogiston theory essentially dead, but the old chemistry based on the Aristotelian Four Elements as vague qualities are now replaced by a new chemistry quantitatively based on the concept of elements as irreducible simple substances. Lavoisier's use of the chemical balance shifted the emphasis in chemistry from qualities to quantities. He also introduced a new system of nomenclature - a system of naming which is essentially the one used today.
  Lavoisier's oxygen theory is important for two reasons:
  (1) It overthrew the Aristotelian concept of element and the Four Elements.
  Air was not an element but a mixture of gases.
  Water was not an element but a compound substance of the elements oxygen and hyrogen.
  Earth was not an element but a mixture of compounds and elements; the metals were not compounds but elements.
  Only the element Fire remained; but no longer as phlogiston but the weightless heat substance caloric.
  Aristotle's fifth element, the "quintessence", had already been transformed into the weightless, penetrable substance called "aether".
  (2) It set chemistry on a modern foundation. Chemistry was no longer just a qualitative science but was quantitative. The chemical balance would be the decisive instrument of chemical research. This led to the basic law of chemistry: the conservation of matter. In his Traite Elementaire de Chimie Lavoiser states,
  "The whole art of making experiments in chemistry is founded on this principle: we must always suppose an exact equality or equation between the principles of the body examined and those of the products of its analysis."
  Here is a restatement of the Greek concept of the indestructibilty of matter, but with a major difference: the exact equality or equation is subject to quantitative experimentation.
  For these reasons, Lavoiser deserves the title of the "Father of Modern Chemistry." It was a real loss when he fell victim to the French Revolution. Because of his association with the hated tax-collection agency, the fermiers generaux of the monarchist France, he was beheaded in 1794. The great French mathematician Joseph Lagrange (1736-1815) observed, "It took only a moment to sever that head, but France will not produce another like it in a century."