In 1802, French
American chemist and industrialist Éleuthère Irénée du Pont, who learned
manufacture of gunpowder and explosives under Antoine Lavoisier, founded a
gunpowder manufacturer in Delaware known as E. I. du Pont de Nemours and Company. The French Revolution forced his family to move to the United States where du
Pont started a gunpowder mill on the Brandywine River in Delaware. Wanting to make the best powder possible, du
Pont was vigilant about the quality of the materials he used. For 32 years, du
Pont served as president of E. I. du Pont de Nemours and Company, which
eventually grew into one of the largest and most successful companies in
America.
Throughout the
19th century, chemistry was divided between those who followed the atomic
theory of John Dalton and those who did
not, such as Wilhelm Ostwald and Ernst Mach. Although such proponents of the atomic theory as Amedeo Avogadro and Ludwig Boltzmann made great advances in explaining the behavior of gases, this dispute was not
finally settled until Jean Perrin's experimental investigation of Einstein's atomic explanation of Brownian motion in the first decade of the 20th century.
Well before the
dispute had been settled, many had already applied the concept of atomism to
chemistry. A major example was the ion theory of Svante Arrhenius which anticipated ideas about atomic substructure that did not
fully develop until the 20th century. Michael Faraday was another early worker, whose major contribution to
chemistry was electrochemistry, in which (among other
things) a certain quantity of electricity during electrolysis or electrodeposition of metals was shown
to be associated with certain quantities of chemical elements, and fixed
quantities of the elements therefore with each other, in specific
ratios. These findings, like those of Dalton's combining ratios, were
early clues to the atomic nature of matter.
In 1803,
English meteorologist and chemist John Dalton proposed Dalton's law, which describes the relationship between the components in a
mixture of gases and the relative pressure each contributes to that of the
overall mixture. Discovered in 1801, this concept is also known as
Dalton's law of partial pressures.
Dalton also
proposed a modern atomic theory in 1803 which stated that all matter was composed of small
indivisible particles termed atoms, atoms of a given element possess unique
characteristics and weight, and three types of atoms exist: simple (elements),
compound (simple molecules), and complex (complex molecules). In 1808, Dalton
first published New System of Chemical Philosophy (1808-1827),
in which he outlined the first modern scientific description of the atomic
theory. This work identified chemical elements as a specific type of atom,
therefore rejecting Newton's theory of chemical affinities.
Instead, Dalton
inferred proportions of elements in compounds by taking ratios of the weights
of reactants, setting the atomic weight of hydrogen to be identically one.
Following Jeremias Benjamin
Richter (known
for introducing the term stoichiometry), he proposed that chemical elements combine in integral
ratios. This is known as the law of multiple
proportions or
Dalton's law, and Dalton included a clear description of the law in his New
System of Chemical Philosophy. The law of multiple proportions is one of
the basic laws of stoichiometry used to establish the atomic theory. Despite
the importance of the work as the first view of atoms as physically real
entities and introduction of a system of chemical symbols, New System
of Chemical Philosophy devoted almost as much space to the caloric
theory as to atomism.
French
chemist Joseph Proust proposed the law of definite
proportions,
which states that elements always combine in small, whole number ratios to form
compounds, based on several experiments conducted between 1797 and
1804 Along with the law of multiple proportions, the law of definite
proportions forms the basis of stoichiometry. The law of definite proportions
and constant composition do not prove that atoms exist, but they are difficult
to explain without assuming that chemical compounds are formed when atoms
combine in constant proportions.
A Swedish
chemist and disciple of Dalton, Jöns Jacob Berzelius embarked on a
systematic program to try to make accurate and precise quantitative
measurements and insure the purity of chemicals. Along with Lavoisier, Boyle,
and Dalton, Berzelius is known as the father of modern chemistry. In 1828 he
compiled a table of relative atomic weights, where oxygen was set to 100, and which included all of the elements
known at the time. This work provided evidence in favor of Dalton's atomic
theory: that inorganic chemical compounds are composed of atoms combined
in whole number amounts. He determined the exact
elementary constituents of large numbers of compounds. The results strongly
confirmed Proust's Law of Definite Proportions. In his weights, he used oxygen
as a standard, setting its weight equal to exactly 100. He also measured the
weights of 43 elements. In discovering that atomic weights are not integer
multiples of the weight of hydrogen, Berzelius also disproved Prout's hypothesisthat elements are built up
from atoms of hydrogen.
Motivated by
his extensive atomic weight determinations and in a desire to aid his
experiments, he introduced the classical system of chemical symbols and
notation with his 1808 publishing of Lärbok i Kemien, in which
elements are abbreviated by one or two letters to make a distinct abbreviation
from their Latin name. This system of chemical notation—in which the elements
were given simple written labels, such as O for oxygen, or Fe for iron, with
proportions noted by numbers—is the same basic system used today. The only
difference is that instead of the subscript number used today (e.g., H2O),
Berzelius used a superscript (H2O). Berzelius is credited with
identifying the chemical elements silicon, selenium, thorium, and cerium. Students working in
Berzelius's laboratory also discovered lithium and vanadium.
Berzelius
developed the radical theory of chemical combination, which holds that
reactions occur as stable groups of atoms called radicals are exchanged
between molecules. He believed that salts are compounds of an acid and bases, and discovered that the anions in acids would be attracted to
a positive electrode (the anode), whereas the cations in
a base would be attracted to a negative electrode (the cathode). Berzelius did not believe in the Vitalism Theory, but instead in a regulative force which produced
organization of tissues in an organism. Berzelius is also credited with
originating the chemical terms "catalysis", "polymer", "isomer", and "allotrope", although his original definitions differ dramatically
from modern usage. For example, he coined the term "polymer" in 1833
to describe organic compounds which shared identical empirical formulas but
which differed in overall molecular weight, the larger of the compounds being
described as "polymers" of the smallest. By this long superseded,
pre-structural definition, glucose (C6H12O6) was viewed as a
polymer of formaldehyde (CH2O).
English
chemist Humphry Davy was a pioneer in the
field of electrolysis, using Alessandro Volta's
voltaic pile to split up common compounds and thus isolate a series of new
elements. He went on to electrolyse molten salts and discovered several new
metals, especially sodium and potassium, highly reactive elements known as the alkali metals. Potassium, the first metal that was isolated by electrolysis,
was discovered in 1807 by Davy, who derived it from caustic potash (KOH). Before the
19th century, no distinction was made between potassium and sodium. Sodium was
first isolated by Davy in the same year by passing an electric current through
molten sodium hydroxide (NaOH). When Davy
heard that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime
in mercury, he tried it himself. Davy was successful, and discovered calcium in 1808 by electrolyzing a mixture of lime and mercuric oxide. He worked with electrolysis throughout his life and, in
1808, he isolated magnesium, strontium and barium.
Davy also
experimented with gases by inhaling them. This experimental procedure nearly
proved fatal on several occasions, but led to the discovery of the unusual
effects of nitrous oxide, which came to be known
as laughing gas. Chlorine was discovered in
1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated
marine acid" (see phlogiston theory) and mistakenly thought it contained oxygen. Scheele observed several properties of chlorine gas, such as
its bleaching effect on litmus, its deadly effect on insects, its yellow-green
colour, and the similarity of its smell to that of aqua regia. However, Scheele was unable to publish his findings at the
time. In 1810, chlorine was given its current name by Humphry Davy (derived
from the Greek word for green), who insisted that chlorine was in fact an element.[63] He also showed that oxygen could not be obtained from the substance known as oxymuriatic acid (HCl
solution). This discovery overturned Lavoisier's definition of acids as compounds of oxygen. Davy was a
popular lecturer and able experimenter.
French
chemist Joseph Louis Gay-Lussac shared the interest
of Lavoisier and others in the quantitative study of the properties of gases.
From his first major program of research in 1801–1802, he concluded that equal
volumes of all gases expand equally with the same increase in temperature: this
conclusion is usually called "Charles's law", as Gay-Lussac gave credit to Jacques Charles, who had arrived at nearly the same conclusion in the 1780s but
had not published it. The law was independently discovered by British
natural philosopher John Dalton by 1801, although Dalton's description was less
thorough than Gay-Lussac's. In 1804 Gay-Lussac made several daring ascents
of over 7,000 meters above sea level in hydrogen-filled balloons—a feat not
equaled for another 50 years—that allowed him to investigate other aspects of
gases. Not only did he gather magnetic measurements at various altitudes, but
he also took pressure, temperature, and humidity measurements and samples of
air, which he later analyzed chemically.
In 1808
Gay-Lussac announced what was probably his single greatest achievement: from
his own and others' experiments he deduced that gases at constant temperature
and pressure combine in simple numerical proportions by volume, and the
resulting product or products—if gases—also bear a simple proportion by volume
to the volumes of the reactants. In other words, gases under equal conditions
of temperature and pressure react with one another in volume ratios of small
whole numbers. This conclusion subsequently became known as "Gay-Lussac's law" or the "Law of Combining
Volumes".
With his fellow professor at the École Polytechnique, Louis Jacques Thénard, Gay-Lussac also
participated in early electrochemical research, investigating the elements
discovered by its means. Among other achievements, they decomposed boric acid by using fused potassium, thus discovering the
element boron. The two also took part in contemporary debates that modified
Lavoisier's definition of acids and furthered his program of analyzing organic
compounds for their oxygen and hydrogen content.
The
element iodine was discovered by
French chemist Bernard Courtois in 1811. Courtois gave samples to his friends, Charles Bernard
Desormes (1777–1862)
and Nicolas Clément (1779–1841), to
continue research. He also gave some of the substance to Gay-Lussac and to
physicist André-Marie Ampère. On December 6, 1813,
Gay-Lussac announced that the new substance was either an element or a compound
of oxygen. It was Gay-Lussac who suggested the name "iode",
from the Greek word ιώδες (iodes) for violet (because of the color of iodine
vapor). Ampère had given some of his sample to Humphry Davy. Davy did some
experiments on the substance and noted its similarity to chlorine. Davy
sent a letter dated December 10 to the Royal Society of London stating that he had
identified a new element. Arguments erupted between Davy and Gay-Lussac
over who identified iodine first, but both scientists acknowledged Courtois as
the first to isolate the element.
In 1815,
Humphry Davy invented the Davy lamp, which allowed miners within coal mines to work safely in the presence of flammable gases. There
had been many mining explosions caused by firedamp or methane often ignited by open flames of the lamps then used by
miners. Davy conceived of using an iron gauze to enclose a lamp's flame, and so
prevent the methane burning inside the lamp from passing out to the general
atmosphere. Although the idea of the safety lamp had already been demonstrated by William Reid Clanny and by the then
unknown (but later very famous) engineer George Stephenson, Davy's use of wire gauze to prevent the spread of flame was
used by many other inventors in their later designs. There was some discussion
as to whether Davy had discovered the principles behind his lamp without the
help of the work of Smithson Tennant, but it was generally agreed that the work of both men had been
independent. Davy refused to patent the lamp, and its invention led to him
being awarded the Rumford medal in 1816.
After Dalton
published his atomic theory in 1808, certain of his central ideas were soon
adopted by most chemists. However, uncertainty persisted for half a century
about how atomic theory was to be configured and applied to concrete
situations; chemists in different countries developed several different
incompatible atomistic systems. A paper that suggested a way out of this
difficult situation was published as early as 1811 by the Italian
physicist Amedeo Avogadro (1776-1856), who
hypothesized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules, from which it followed
that relative molecular weights of any two gases are the same as the ratio of the
densities of the two gases under the same conditions of temperature and
pressure. Avogadro also reasoned that simple gases were not formed of solitary
atoms but were instead compound molecules of two or more atoms. Thus Avogadro
was able to overcome the difficulty that Dalton and others had encountered when
Gay-Lussac reported that above 100 °C the volume of water vapor was twice
the volume of the oxygen used to form it. According to Avogadro, the molecule
of oxygen had split into two atoms in the course of forming water vapor.
Avogadro's
hypothesis was neglected for half a century after it was first published. Many
reasons for this neglect have been cited, including some theoretical problems,
such as Jöns Jacob Berzelius's "dualism", which asserted that
compounds are held together by the attraction of positive and negative electrical
charges, making it inconceivable that a molecule composed of two electrically
similar atoms—as in oxygen—could exist. An additional barrier to acceptance was
the fact that many chemists were reluctant to adopt physical methods (such as
vapour-density determinations) to solve their problems. By mid-century,
however, some leading figures had begun to view the chaotic multiplicity of
competing systems of atomic weights and molecular formulas as intolerable.
Moreover, purely chemical evidence began to mount that suggested Avogadro's
approach might be right after all. During the 1850s, younger chemists, such
as Alexander Williamson in England, Charles Gerhardt and Charles-Adolphe Wurtz in France, and August Kekulé in Germany, began to advocate reforming theoretical
chemistry to make it consistent with Avogadrian theory.
In 1825, Friedrich Wöhler and Justus von Liebig performed the first confirmed discovery and explanation
of isomers, earlier named by Berzelius. Working with cyanic acid and fulminic acid,
they correctly deduced that isomerism was caused by differing arrangements of
atoms within a molecular structure. In 1827, William Prout classified biomolecules into their modern groupings: carbohydrates, proteinsand lipids. After the nature of
combustion was settled, a dispute about vitalism and the essential distinction between organic and
inorganic substances began. The vitalism question was revolutionized in 1828
when Friedrich Wöhler synthesized urea, thereby establishing
that organic compounds could be produced from inorganic starting materials and
disproving the theory of vitalism.
This opened a
new research field in chemistry, and by the end of the 19th century, scientists
were able to synthesize hundreds of organic compounds. The most important among
them are mauve, magenta, and other
synthetic dyes, as well as the widely used drug aspirin. The discovery of the artificial synthesis of urea contributed
greatly to the theory of isomerism, as the empirical chemical formulas for urea and ammonium cyanate are identical (see Wöhler synthesis). In 1832, Friedrich Wöhler
and Justus von Liebig discovered and explained functional groups and radicals in relation to
organic chemistry, as well as first synthesizing benzaldehyde. Liebig, a German chemist, made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry. Liebig is considered the "father of the fertilizer industry" for his discovery of nitrogen as an essential plant nutrient, and his formulation of the Law of the Minimum which described the
effect of individual nutrients on crops.
In 1840, Germain Hess proposed Hess's law, an early statement of the law of conservation of
energy,
which establishes that energy changes in a chemical process depend only on the states of
the starting and product materials and not on the specific pathway taken
between the two states. In 1847, Hermann Kolbe obtained acetic acid from completely inorganic sources, further disproving
vitalism. In 1848, William Thomson, 1st
Baron Kelvin (commonly
known as Lord Kelvin) established the concept of absolute zero, the temperature at which all molecular motion ceases. In
1849, Louis Pasteur discovered that
the racemic form of tartaric acid is a mixture of the levorotatory and dextrotatory forms,
thus clarifying the nature of optical rotation and advancing the field of stereochemistry.
In 1852, August Beer proposed Beer's law, which explains the relationship between the composition of a
mixture and the amount of light it will absorb. Based partly on earlier work
by Pierre Bouguerand Johann Heinrich Lambert, it established the analytical technique known
as spectrophotometry. In 1855, Benjamin Silliman, Jr. pioneered methods
of petroleum cracking, which made the entire
modern petrochemical industry possible.
Avogadro's
hypothesis began to gain broad appeal among chemists only after his compatriot
and fellow scientist Stanislao Cannizzaro demonstrated its
value in 1858, two years after Avogadro's death. Cannizzaro's chemical
interests had originally centered on natural products and on reactions of aromatic compounds; in 1853 he discovered that when benzaldehyde is treated with concentrated base, both benzoic acid and benzyl alcohol are produced—a phenomenon known today as the Cannizzaro reaction. In his 1858 pamphlet,
Cannizzaro showed that a complete return to the ideas of Avogadro could be used
to construct a consistent and robust theoretical structure that fit nearly all
of the available empirical evidence. For instance, he pointed to evidence that
suggested that not all elementary gases consist of two atoms per molecule—some
were monatomic, most were diatomic, and a few were even more complex.
Another point
of contention had been the formulas for compounds of the alkali metals (such as sodium) and the alkaline earth metals (such as calcium), which, in view of their striking chemical analogies, most
chemists had wanted to assign to the same formula type. Cannizzaro argued that
placing these metals in different categories had the beneficial result of
eliminating certain anomalies when using their physical properties to deduce
atomic weights. Unfortunately, Cannizzaro's pamphlet was published initially
only in Italian and had little immediate impact. The real breakthrough came
with an international chemical
congress held
in the German town of Karlsruhe in September 1860, at which most of the leading European
chemists were present. The Karlsruhe Congress had been arranged by Kekulé,
Wurtz, and a few others who shared Cannizzaro's sense of the direction
chemistry should go. Speaking in French (as everyone there did), Cannizzaro's
eloquence and logic made an indelible impression on the assembled body.
Moreover, his friend Angelo Pavesi distributed Cannizzaro's pamphlet to
attendees at the end of the meeting; more than one chemist later wrote of the
decisive impression the reading of this document provided. For instance, Lothar Meyer later wrote that on reading
Cannizzaro's paper, "The scales seemed to fall from my
eyes." Cannizzaro thus played a crucial role in winning the battle
for reform. The system advocated by him, and soon thereafter adopted by most
leading chemists, is substantially identical to what is still used today.
In 1856,
Sir William Henry Perkin, age 18, given a
challenge by his professor, August Wilhelm von
Hofmann,
sought to synthesize quinine, the anti-malaria drug, from coal tar. In one attempt, Perkin oxidized aniline using potassium dichromate, whose toluidine impurities reacted with the aniline and yielded a black
solid—suggesting a "failed" organic synthesis. Cleaning the flask
with alcohol, Perkin noticed purple portions of the solution: a byproduct of
the attempt was the first synthetic dye, known as mauveine or
Perkin's mauve. Perkin's discovery is the foundation of the dye synthesis
industry, one of the earliest successful chemical industries.
German
chemist August Kekulé von Stradonitz's most important single
contribution was his structural theory of organic composition, outlined in two
articles published in 1857 and 1858 and treated in great detail in the pages of
his extraordinarily popular Lehrbuch der organischen Chemie ("Textbook
of Organic Chemistry"), the first installment of which appeared in 1859
and gradually extended to four volumes. Kekulé argued that tetravalent carbon atoms - that is, carbon forming exactly four chemical bonds - could link together to form what he called a
"carbon chain" or a "carbon skeleton," to which other atoms
with other valences (such as hydrogen, oxygen, nitrogen, and chlorine) could
join. He was convinced that it was possible for the chemist to specify this
detailed molecular architecture for at least the simpler organic compounds
known in his day. Kekulé was not the only chemist to make such claims in this
era. The Scottish chemist Archibald Scott Couper published a
substantially similar theory nearly simultaneously, and the Russian
chemist Aleksandr Butlerov did much to clarify and
expand structure theory. However, it was predominantly Kekulé's ideas that
prevailed in the chemical community.
British chemist
and physicist William Crookes is noted for his cathode ray studies, fundamental in the development of atomic physics. His researches on electrical discharges through a rarefied gas
led him to observe the dark space around the cathode, now called the Crookes
dark space. He demonstrated that cathode rays travel in straight lines and
produce phosphorescence and heat when they strike certain materials. A pioneer
of vacuum tubes, Crookes invented the Crookes tube - an early experimental discharge tube, with partial
vacuum with which he studied the behavior of cathode rays. With the
introduction of spectrum analysis by Robert Bunsen and Gustav Kirchhoff (1859-1860), Crookes applied the new technique to the
study of selenium compounds. Bunsen
and Kirchhoff had previously used spectroscopy as a means of chemical analysis
to discover caesium and rubidium. In 1861, Crookes used this process to discover thallium in some seleniferous deposits. He continued work on that
new element, isolated it, studied its properties, and in 1873 determined its
atomic weight. During his studies of thallium, Crookes discovered the principle
of the Crookes radiometer, a device that converts
light radiation into rotary motion. The principle of this radiometer has found
numerous applications in the development of sensitive measuring instruments.
In 1862, Alexander Parkes exhibited Parkesine,
one of the earliest synthetic polymers, at the International Exhibition in London.
This discovery formed the foundation of the modern plastics industry. In 1864, Cato Maximilian
Guldberg and Peter Waage, building on Claude Louis Berthollet's ideas, proposed
the law of mass action. In 1865, Johann Josef Loschmidtdetermined the exact
number of molecules in a mole, later named Avogadro's number.
In 1865, August
Kekulé, based partially on the work of Loschmidt and others, established the
structure of benzene as a six carbon ring with alternating single and double bonds. Kekulé's novel proposal for benzene's cyclic structure was
much contested but was never replaced by a superior theory. This theory
provided the scientific basis for the dramatic expansion of the German chemical
industry in the last third of the 19th century. Today, the large majority of
known organic compounds are aromatic, and all of them contain at least one
hexagonal benzene ring of the sort that Kekulé advocated. Kekulé is also famous
for having clarified the nature of aromatic compounds, which are compounds
based on the benzene molecule. In 1865, Adolf von Baeyer began work on indigo dye, a milestone in modern industrial organic chemistry which
revolutionized the dye industry.
Swedish chemist and inventor Alfred Nobel found that when nitroglycerin was incorporated in an absorbent inert substance
like kieselguhr (diatomaceous earth) it became safer and more
convenient to handle, and this mixture he patented in 1867 as dynamite. Nobel later on combined nitroglycerin with various
nitrocellulose compounds, similar to collodion, but settled on a more efficient recipe combining another
nitrate explosive, and obtained a transparent, jelly-like substance, which was
a more powerful explosive than dynamite. Gelignite, or blasting gelatin, as it was named, was patented in 1876;
and was followed by a host of similar combinations, modified by the addition
of potassium nitrate and various other
substances.
Dmitri Mendeleev,
responsible for organizing the known chemical elements in a periodic table. An
important breakthrough in making sense of the list of known chemical elements
(as well as in understanding the internal structure of atoms) was Dmitri Mendeleev's
development of the first modern periodic table, or the
periodic classification of the elements. Mendeleev, a Russian chemist, felt
that there was some type of order to the elements and he spent more than
thirteen years of his life collecting data and assembling the concept,
initially with the idea of resolving some of the disorder in the field for his
students. Mendeleev found that, when all the known chemical elements were
arranged in order of increasing atomic weight, the resulting table displayed a
recurring pattern, or periodicity, of properties within groups of elements.
Mendeleev's law allowed him to build up a systematic periodic table of all the
66 elements then known based on atomic mass, which he published in Principles
of Chemistry in 1869. His first Periodic Table was compiled on the basis
of arranging the elements in ascending order of atomic weight and grouping them
by similarity of properties.
Mendeleev had
such faith in the validity of the periodic law that he proposed changes to the
generally accepted values for the atomic weight of a few elements and, in his
version of the periodic table of 1871, predicted the locations within the table
of unknown elements together with their properties. He even predicted the
likely properties of three yet-to-be-discovered elements, which he called ekaboron (Eb), ekaaluminium (Ea), and
ekasilicon (Es), which proved to be good predictors of the
properties of scandium, gallium, and germanium, respectively, which each fill the spot in the periodic table
assigned by Mendeleev.
At first the
periodic system did not raise interest among chemists. However, with the
discovery of the predicted elements, notably gallium in 1875, scandium in 1879,
and germanium in 1886, it began to win wide acceptance. The subsequent proof of
many of his predictions within his lifetime brought fame to Mendeleev as the
founder of the periodic law. This organization surpassed earlier attempts at
classification by Alexandre-Émile Béguyer
de Chancourtois, who published the telluric helix, an early, three-dimensional
version of the periodic table of the elements in 1862, John Newlands, who proposed the law of
octaves (a precursor to the periodic law) in 1864, and Lothar Meyer, who developed an early version of
the periodic table with 28 elements organized by valence in 1864. Mendeleev's
table did not include any of the noble gases, however, which had not yet been discovered. Gradually the
periodic law and table became the framework for a great part of chemical
theory. By the time Mendeleev died in 1907, he enjoyed international
recognition and had received distinctions and awards from many countries.
In 1873, Jacobus Henricus van 't
Hoff and Joseph Achille Le Bel, working independently,
developed a model of chemical bonding that explained the chirality experiments of Pasteur and
provided a physical cause for optical activity in chiral compounds. van 't Hoff's publication,
called Voorstel tot Uitbreiding der Tegenwoordige in de Scheikunde gebruikte
Structuurformules in de Ruimte, etc. (Proposal for the development of
3-dimensional chemical structural formulae) and consisting of twelve pages text
and one page diagrams, gave the impetus to the development of stereochemistry. The concept of the "asymmetrical carbon atom", dealt
with in this publication, supplied an explanation of the occurrence of numerous
isomers, inexplicable by means of the then current structural formulae. At the
same time he pointed out the existence of relationship between optical activity
and the presence of an asymmetrical carbon atom.
American
mathematical physicist J. Willard Gibbs's work on the
applications of thermodynamics was instrumental in transforming physical chemistry into a rigorous
deductive science. During the years from 1876 to 1878, Gibbs worked on the
principles of thermodynamics, applying them to the complex processes involved
in chemical reactions. He discovered the concept of chemical potential, or the "fuel"
that makes chemical reactions work. In 1876 he published his most famous
contribution, "On the
Equilibrium of Heterogeneous Substances", a compilation of his work on
thermodynamics and physical chemistry which laid out the concept of free energy to explain the
physical basis of chemical equilibria. In these essays were the beginnings
of Gibbs’ theories of phases of matter: he considered each state of matter a
phase, and each substance a component. Gibbs took all of the variables involved
in a chemical reaction - temperature, pressure, energy, volume, and entropy -
and included them in one simple equation known as Gibbs' phase rule.
Within this
paper was perhaps his most outstanding contribution, the introduction of the
concept free energy, now universally called Gibbs free energy in his honor. The Gibbs free energy relates the tendency
of a physical or chemical system to simultaneously lower its energy and
increase its disorder, or entropy, in a spontaneous natural process. Gibbs's approach allows a
researcher to calculate the change in free energy in the process, such as in a
chemical reaction, and how fast it will happen. Since virtually all chemical
processes and many physical ones involve such changes, his work has
significantly impacted both the theoretical and experiential aspects of these
sciences. In 1877, Ludwig Boltzmann established statistical derivations of many important physical
and chemical concepts, including entropy, and distributions of molecular velocities in the gas
phase. Together with Boltzmann and James Clerk Maxwell, Gibbs created a new branch
of theoretical physics called statistical mechanics (a term that he
coined), explaining the laws of thermodynamics as consequences of the
statistical properties of large ensembles of particles. Gibbs also worked on
the application of Maxwell's equations to problems in physical optics. Gibbs's
derivation of the phenomenological laws of thermodynamics from the statistical
properties of systems with many particles was presented in his highly
influential textbook Elementary Principles in Statistical Mechanics, published in 1902, a
year before his death. In that work, Gibbs reviewed the relationship between
the laws of thermodynamics and statistical theory of molecular motions. The
overshooting of the original function by partial sums of Fourier series at points of discontinuity is known as the Gibbs phenomenon.
German
engineer Carl von Linde's invention of a
continuous process of liquefying gases in large quantities formed a basis for
the modern technology of refrigerationand
provided both impetus and means for conducting scientific research at low
temperatures and very high vacuums. He developed a methyl ether refrigerator (1874) and an ammonia refrigerator (1876).
Though other refrigeration units had been developed earlier, Linde's were the
first to be designed with the aim of precise calculations of efficiency. In
1895 he set up a large-scale plant for the production of liquid air. Six years
later he developed a method for separating pure liquid oxygen from liquid air
that resulted in widespread industrial conversion to processes utilizing oxygen
(e.g., in steel manufacture).
In 1883, Svante Arrhenius developed an ion theory to explain
conductivity in electrolytes.[82] In 1884, Jacobus Henricus van 't
Hoff published Études
de Dynamique chimique (Studies in Dynamic Chemistry), a seminal study
on chemical kinetics. In this work, van
't Hoff entered for the first time the field of physical chemistry. Of great
importance was his development of the general thermodynamic relationship
between the heat of conversion and the displacement of the equilibrium as a
result of temperature variation. At constant volume, the equilibrium in a
system will tend to shift in such a direction as to oppose the temperature
change which is imposed upon the system. Thus, lowering the temperature results
in heat development while increasing the temperature results in heat
absorption. This principle of mobile equilibrium was subsequently (1885) put in
a general form by Henry Louis Le
Chatelier,
who extended the principle to include compensation, by change of volume, for
imposed pressure changes. The van 't Hoff-Le Chatelier principle, or
simply Le Chatelier's
principle,
explains the response of dynamic chemical equilibria to external
stresses.
In 1884, Hermann Emil Fischer proposed the
structure of purine, a key structure in many
biomolecules, which he later synthesized in 1898. He also began work on the
chemistry of glucose and related sugars. In 1885, Eugene Goldstein named the cathode ray, later discovered to be composed of electrons, and the canal ray, later discovered to be positive hydrogen ions that had been
stripped of their electrons in a cathode ray tube; these would later be named protons. The year 1885 also saw the publishing of J. H. van 't
Hoff's L'Équilibre chimique dans les Systèmes gazeux ou dissous à
I'État dilué (Chemical equilibria in gaseous systems or strongly
diluted solutions), which dealt with this theory of dilute solutions. Here he
demonstrated that the "osmotic pressure" in solutions which are sufficiently dilute is
proportionate to the concentration and the absolute temperature so that this pressure can be
represented by a formula which only deviates from the formula for gas pressure
by a coefficient i. He also determined the value of i by
various methods, for example by means of the vapor pressure and François-Marie Raoult's results on the lowering
of the freezing point. Thus van 't Hoff was able to prove that thermodynamic
laws are not only valid for gases, but also for dilute solutions. His pressure
laws, given general validity by the electrolytic dissociation theory of
Arrhenius (1884-1887) - the first foreigner who came to work with him in
Amsterdam (1888) - are considered the most comprehensive and important in the
realm of natural sciences. In 1893, Alfred Werner discovered the octahedral structure of cobalt complexes,
thus establishing the field of coordination chemistry.
The most
celebrated discoveries of Scottish chemist William Ramsay were made in inorganic chemistry. Ramsay was intrigued by
the British physicist John Strutt, 3rd Baron
Rayleigh's
1892 discovery that the atomic weight of nitrogen found in chemical compounds was lower than that of
nitrogen found in the atmosphere. He ascribed this discrepancy to a light gas
included in chemical compounds of nitrogen, while Ramsay suspected a hitherto
undiscovered heavy gas in atmospheric nitrogen. Using two different methods to
remove all known gases from air, Ramsay and Lord Rayleigh were able to announce
in 1894 that they had found a monatomic, chemically inert gaseous element that
constituted nearly 1 percent of the atmosphere; they named it argon.
The following
year, Ramsay liberated another inert gas from a mineral called cleveite; this proved to be helium, previously known only in the solar spectrum. In his book The
Gases of the Atmosphere (1896), Ramsay showed that the positions of
helium and argon in the periodic table of elements indicated that at least
three more noble gases might exist. In 1898 Ramsay and the British
chemist Morris W. Travers isolated these
elements—called neon, krypton, and xenon—from air brought to a
liquid state at low temperature and high pressure. Sir William Ramsay worked
with Frederick Soddy to demonstrate, in
1903, that alpha particles (helium nuclei) were continually produced during the
radioactive decay of a sample of radium. Ramsay was awarded the 1904 Nobel Prize for
Chemistry in
recognition of "services in the discovery of the inert gaseous elements in
air, and his determination of their place in the periodic system."
In 1897, J. J. Thomson discovered the electron using the cathode ray tube. In 1898, Wilhelm Wien demonstrated that canal rays (streams of positive ions)
can be deflected by magnetic fields, and that the amount of deflection is
proportional to the mass-to-charge ratio. This discovery would
lead to the analytical technique known
as mass spectrometry in 1912.
Norb Leahy, Dunwoody GA Tea Party Leader
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