Gay Lussac

Gay-Lussac

Joseph Louis Gay-Lussac (1778–1850) grew up during both the French and Chemical Revolutions. His comfortable existence as the privately tutored son of a well-to-do lawyer was disrupted by political and social upheavals: his tutor fled, and his father was imprisoned. Joseph, however, benefited from the new order when he was selected to attend the École Polytechnique, an institution of the French Revolution designed to create scientific and technical leadership, especially for the military. There his mentors included Pierre Simon de Laplace and Claude Louis Berthollet, among other scientists converted by Antoine-Laurent Lavoisier to oxygen chemistry. Gay-Lussac’s own career as a professor of physics and chemistry began at the École Polytechnique

Law of Combining Volumes of Gases

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. This conclusion subsequently became known as Gay-Lussac’s law.

Other Achievements

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.

When they heard of the English chemist Humphry Davy’s isolation of the newly discovered reactive metals sodium and potassium by electrolysis in 1807, they worked to produce even larger quantities of the metals by chemical means and tested their reactivity in various experiments. Notably they isolated the new element boron. They also studied the effect of light on reactions between hydrogen and chlorine, though it was Davy who demonstrated that the latter gas was an element. Rivalry between Gay-Lussac and Davy reached a climax over the iodine experiments Davy carried out during an extraordinary visit to Paris in November 1813, at a time when France was at war with Britain. Both chemists claimed priority over discovering iodine’s elemental nature. Although Davy is typically given credit for this discovery, most of his work was hurried and incomplete. Gay-Lussac presented a much more complete study of iodine in a long memoir presented to the National Institute on August 1, 1814, and subsequently published in the Annales de chimie. In 1815 Gay-Lussac experimentally demonstrated that prussic acid was simply hydrocyanic acid, a compound of carbon, hydrogen, and nitrogen, and he also isolated the compound cyanogen [(CN)2 or C2N2]. His analyses of prussic acid and hydriodic acid (HI) necessitated a modification of Antoine Lavoisier’s theory that oxygen was present in all acids.

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.

A C Avogadro

Lorenzo Romano Amedeo Carlo Avogadro was born in Turin to a noble family of the Kingdom of Sardinia (now part of Italy) in the year 1776. He graduated in ecclesiastical law at the late age of 20 and began to practice. Soon after, he dedicated himself to physics and mathematics (then called positive philosophy), and in 1809 started teaching them at a high school in Vercelli, where his family lived and had some property.

In 1811, he published an article with the title "Essay on Determining the Relative Masses of the Elementary Molecules of Bodies and the Proportions by Which They Enter These Combinations". which contains Avogadro's hypothesis. Avogadro submitted this essay to Jean-Claude Delamétherie's Journal "Journal of Physics, Chemistry and Natural History".

In 1820, he became a professor of physics at the University of Turin. Turin was now the capital of the restored Savoyard Kingdom of Sardinia under Victor Emmanuel I. Avogadro was active in the revolutionary movement of March 1821. As a result, he lost his chair in 1823 (or, as the university officially declared, it was "very glad to allow this interesting scientist to take a rest from heavy teaching duties, in order to be able to give better attention to his researches"). Eventually, King Charles Albert granted a Constitution in 1848. Well before this, Avogadro had been recalled to the university in Turin in 1833, where he taught for another twenty years.

Little is known about Avogadro's private life, which appears to have been sober and religious. He married Felicita Mazzé and had six children. Avogadro held posts dealing with statistics, meteorology, and weights and measures (he introduced the metric system into Piedmont) and was a member of the Royal Superior Council on Public Instruction.

In honor of Avogadro's contributions to molecular theory, the number of molecules per mole of substance is named the "Avogadro constant", NA. It is exactly 6.02214076×1023 mol−1. The Avogadro constant is used to compute the results of chemical reactions. It allows chemists to determine the amounts of substances produced in a given reaction to a great degree of accuracy.

Avogadro's Law states that the relationship between the masses of the same volume of all gases (at the same temperature and pressure) corresponds to the relationship between their respective molecular weights. Hence, the relative molecular mass of a gas can be calculated from the mass of a sample of known volume.

Avogadro developed this hypothesis after Joseph Louis Gay-Lussac published his law on volumes (and combining gases) in 1808.

 The greatest problem Avogadro had to resolve was the confusion at that time regarding atoms and molecules. One of his most important contributions was clearly distinguishing one from the other, stating that gases are composed of molecules, and these molecules are composed of atoms. (For instance, John Dalton did not consider this possibility.).

 Avogadro did not actually use the word "atom" as the words "atom" and "molecule" were used almost without difference. He believed that there were three kinds of "molecules," including an "elementary molecule" (our "atom").

 Also, he gave more attention to the definition of mass, as distinguished from weight.

In 1815, he published "Note on the Relative Masses of Elementary Molecules, or Suggested Densities of Their Gases, and on the Constituents of Some of Their Compounds, As a Follow-up to the Essay on the Same Subject, Published in the Journal of Physics, July 1811" about gas densities.

Unfortunately, related experiments with some inorganic substances showed seeming contradictions. This was finally resolved by Stanislao Cannizzaro, as announced at Karlsruhe Congress in 1860, four years after Avogadro's death. He explained that these exceptions were due to molecular dissociations at certain temperatures, and that Avogadro's law determined not only molecular masses, but atomic masses as well.

In 1911, a meeting in Turin commemorated the hundredth anniversary of the publication of Avogadro's classic 1811 paper. King Victor Emmanuel III attended, and Avogadro's great contribution to chemistry was recognized. Rudolf Clausius, with his kinetic theory on gases proposed in 1857, provided further evidence for Avogadro's Law. Jacobus Henricus van 't Hoff showed that Avogadro's theory also held in dilute solutions.

Jacob Berzelius

Jacob Berzelius was one of the founders of modern chemistry. He was the first person to measure accurate atomic weights for the elements, which helped to confirm Dalton’s Atomic Theory and was the basis of Mendeleev’s periodic table. He discovered three chemical elements: cerium, thorium, and selenium, and devised the modern method by which one or two letters are used to symbolize the elements. He identified and named the phenomenon of catalysis, and described how chemical bonds can form by electrostatic attraction – nowadays called ionic bonding.

Soon after arriving to Stockholm, Berzelius wrote a chemistry textbook for his medical students, Lärboki Kemien, which was his first significant scientific publication. In 1813, he published an essay on the proportions of elements in compounds. The essay commenced with a general description, introduced his new symbolism, examined all the known elements, included a table of specific weights, and finished with a selection of compounds written in his new formalism. In 1818, 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 favour of the atomic theory proposed by John Dalton: that inorganic chemical compounds are composed of atoms combined in whole number amounts. In discovering that atomic weights are not integer multiples of the weight of hydrogen, Berzelius also disproved Prout's hypothesis that elements are built up from atoms of hydrogen. Berzelius's last revised version of his atomic weight tables was first published in a German translation of his Textbook of Chemistry in 1826.

Chemical notation

In order to aid his experiments, he developed a 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. Berzelius thus invented the system of notation still used today, the main difference being that instead of the subscript numbers used today (e.g., H2O), Berzelius used superscripts (H2O).

Discovery of elements

Berzelius is credited with identifying the chemical elements silicon, selenium, thorium, and cerium. Students working in Berzelius's laboratory also discovered lithium, lanthanum and, vanadium. Berzelius discovered silicon by repeating an experiment performed by Gay-Lussac and Thénard. In the experiment, Berzelius reacted silicon tetrafluoride with potassium metal and then purified its product by washing it until it became a brown powder. Berzelius recognized this brown powder as the new element of silicon, which he called silicium, a name proposed earlier by Davy.

Berzelius Measures the Weights of Atoms

Berzelius now embarked on a mammoth series of measurements and analyses of chemicals in order to discover the weights of atoms – if atoms existed. He could not measure atomic weights directly, so his idea was to use oxygen ‘atoms’ as a reference to compare the weights of other atoms with.

First he worked on gas reactions, and by 1818 had built an accurate table of atomic weights for the elements he could study as gases, vaporizing them if necessary.

He then studied reactions of oxygen with metals to deduce the metals’ atomic weights. It was easy to get these wrong, because some metal atoms combine with one oxygen atom, while others combine with two or more oxygen atoms. Utilizing a number of ingenious methods of his own and recent discoveries made by other chemists, such as Dulong and Petit’s Law, and Eilhard Mitscherlich’s discovery of isomorphism, in 1826, Berzelius published a new table of atomic weights. Even from today’s perspective, the accuracy of Berzelius’s atomic weights is impressive.

Berzelius’s atomic weights led to a much wider acceptance of Dalton’s atomic theory, and were the basis of Dmitri Mendeleev’s periodic table in 1869.

Joseph-Louis Proust

Joseph-Louis Proust, also known as Luis Proust, (born Sept. 26, 1754, Angers, France—died July 5, 1826, Angers), French chemist who proved that the relative quantities of any given pure chemical compound’s constituent elements remain invariant, regardless of the compound’s source. This is known as Proust’s law, or the law of definite proportions (1793), and it is the fundamental principle of analytical chemistry. Proust also carried out important applied research in metallurgy, explosives, and nutritional chemistry.

Education and life

The son of an apothecary, Proust prepared for the same occupation, first with his father in Angers and then in Paris, where he also studied chemistry with Hilaire-Martin Rouelle.

In 1776 Proust was appointed a pharmacist at the Salpêtrière Hospital in Paris.

in 1778 Proust abandoned pharmacy to take a professorship of chemistry at the recently established Seminario Patriótico Vascongado in Vergara, Spain.

In 1780 Proust returned to Paris, where he taught chemistry at the Musée, a private teaching institution founded by scientific impresario Jean-François Pilâtre de Rozier. Part of this association involved Proust with aerostatic experiments, which culminated in a balloon ascent with Pilâtre on June 23, 1784, at Versailles, in the presence of the royal court.

In 1786 Proust returned to Spain to teach chemistry, first at Madrid and then in 1788 at the Royal Artillery School in Segovia. The school had been founded in 1764 as part of the program of the government of Charles III to bring Spain abreast of the northern European countries regarding military training. Proust’s chair (and an associated school of chemistry and metallurgy) had been proposed in 1784 to introduce artillery cadets to the latest relevant scientific training. Because of Spain’s scientific backwardness, expert instructors had to be sought abroad. Proust was recommended by no less than the great French chemist Antoine-Laurent Lavoisier.

Proust did not actually assume his chair until 1792, owing to a combination of bureaucratic inefficiency and his own exacting demands for laboratory equipment. When finally ready, his laboratory was undeniably one of the finest in Europe, and Proust probably did the bulk of his practical and analytical chemistry there. Difficulties with the military authorities, though, resulted in Proust’s transfer in 1799 to a chair in chemistry in Madrid.

In 1798 Proust married Anne Rose Chatelain Daubigne, a French resident of Segovia. They returned to France in 1806 under obscure circumstances and settled in Craon, near Angers. Upon the death of his wife in 1817, Proust moved to Angers, where he took over in 1820 the pharmacy of his ailing brother Joachim. Although Proust had returned to France in reduced circumstances, his scientific stature was recognized. He was elected to the French Academy of Sciences to succeed Louis Bernard Guyton de Morveau in 1816; he was made a chevalier of the Legion of Honour in 1819; and he was granted a pension by Louis XVIII in 1820.

Joseph Proust was best known for his analytical abilities. His experiments with inorganic binary compounds - mostly sulfates, sulfides, and metallic oxides - led him to formulate the Law of Constant Composition. The law was first published in a paper on iron oxides in 1794.

The Law of Constant Composition, discovered by Joseph Proust, is also known as the Law of Definite Proportions. It is different from the Law of Multiple Proportions although both stem from Lavoisier's Law of Conservation of Mass.

The French chemist Joseph Proust stated this law the following way: "A chemical compound always contains the same elements combined together in the same proportion by mass."

For example, pure water obtained from different sources such as a river, a well, a spring, the sea, etc., always contains hydrogen and oxygen together in the ratio of 1:8 by mass. Similarly, carbon dioxide (CO2) can be obtained by different methods such as,

• Burning of carbon
• Heating of lime stone
• Applying dilute HCl to marble pieces

Each sample of CO2 contains carbon and oxygen in a 3:8 ratio.

Joseph Proust made his discovery on constant composition in 1797 but it was not accepted by the scientific community until the year of 1808.  The discovery was made when Proust conducted several experiments that proved that cupric, also known as copper 2, always has 5.3 copper parts to 1 part carbon and to 4 parts oxygen.  Using this evidence, Proust was able to faithfully say that chemical compounds always have the same ration of elements.

When Dalton proposed his atomic theory, Proust’s law helped to confirm the hypothesis. According to Dalton, atoms would always combine in simple whole number ratios. For example, all water molecules are alike, consisting of two atoms of hydrogen and one atom of oxygen. Therefore, all water has the same composition. Proust’s law has been confirmed by experiments. For example, water always contains 11.2 percent hydrogen and 88.8 percent oxygen.

Classical chemistry

In Europe, the study of chemistry was conducted by alchemists with the goals of transforming common metals into gold or silver and inventing a chemical elixir that would prolong life. Although these goals were never achieved, there were some important discoveries made in the attempt.

Robert Boyle(1627-1691) studied the behavior of gases and discovered the inverse relationship between volume and pressure of a gas. He also stated that “all reality and change can be described in terms of elementary particles and their motion,” an early understanding of atomic theory. In 1661, he wrote the first chemistry textbook, “The Sceptical Chymist,” which moved the study of substances away from mystical associations with alchemy and toward scientific investigation.

By the 1700s, the Age of Enlightenment had taken root all over Europe. Joseph Priestley (1733-1804) disproved the idea that air was an indivisible element. He showed that it was, instead, a combination of gases when he isolated oxygen and went on to discover seven other discreet gases. Jacques Charles continued Boyles’ work and is known for stating the direct relationship between temperature and pressure of gases.

In 1794, Joseph Proust studied pure chemical compounds and stated the Law of Definite Proportions — a chemical compound will always have its own characteristic ratio of elemental components. Water, for instance, always has a two-to-one ratio of hydrogen to oxygen.

Antoine Lavoisier (1743-1794) was a French chemist who made important contributions to the science. While working as a tax collector, Lavoisier helped to develop the metric system in order to insure uniform weights and measures. He was admitted to the French Academy of Sciences in 1768. Two years later, at age 28, he married the 13-year-old daughter of a colleague. Marie-Anne Lavoisier is known to have assisted her husband in his scientific studies by translating English papers and doing numerous drawings to illustrate his experiments.

Lavoisier’s insistence on meticulous measurement led to his discovery of the Law of Conservation of Mass. In 1787, Lavoisier published "Methods of Chemical Nomenclature," which included the rules for naming chemical compounds that are still in use today. His "Elementary Treatise of Chemistry" (1789) was the first modern chemistry textbook. It clearly defined a chemical element as a substance that cannot be reduced in weight by a chemical reaction and listed oxygen, iron, carbon, sulfur and nearly 30 other elements then known to exist. The book did have a few errors though; it listed light and heat as elements.

Amedeo Avogadro (1776-1856) was an Italian lawyer who began to study science and mathematics in 1800. Expanding on the work of Boyle and Charles, he clarified the difference between atoms and molecules. He went on to state that equal volumes of gas at the same temperature and pressure have the same number of molecules. The number of molecules in a 1-gram molecular weight (1 mole) sample of a pure substance is called Avogadro’s Constant in his honor. It has been experimentally determined to be 6.023 x 1023 molecules and is an important conversion factor used to determine the mass of reactants and products in chemical reactions.

In 1803, an English meteorologist began to speculate on the phenomenon of water vapor.

John Dalton (1766-1844) was aware that water vapor is part of the atmosphere, but experiments showed that water vapor would not form in certain other gases. He speculated that this had something to do with the number of particles present in those gases. Perhaps there was no room in those gases for particles of water vapor to penetrate. There were either more particles in the “heavier” gases or those particles were larger. Using his own data and the Law of Definite Proportions, he determined the relative masses of particles for six of the known elements: hydrogen (the lightest and assigned a mass of 1), oxygen, nitrogen, carbon, sulfur and phosphorous. Dalton explained his findings by stating the principles of the first atomic theory of matter.

1. Elements are composed of extremely small particles called atoms.
2. Atoms of the same element are identical in size, mass and other properties. Atoms of different elements have different properties.
3. Atoms cannot be created, subdivided or destroyed.
4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.
5. In chemical reactions atoms are combined, separated or rearranged to form new compounds.

Dmitri Mendeleev (1834-1907) was a Russian chemist known for developing the first Periodic Table of the Elements. He listed the 63 known elements and their properties on cards. When he arranged the elements in order of increasing atomic mass, he could group elements with similar properties. With a few exceptions, every seventh element had similar properties (The eighth chemical group — the Noble Gases — had not been discovered yet). Mendeleev realized that if he left spaces for the places where no known element fit into the pattern that it was even more exact. Using the blank spaces in his table, he was able to predict the properties of elements that had yet to be discovered. Mendeleev’s original table has been updated to include the 92 naturally occurring elements and 26 synthesized elements.

Describing the atom

In 1896, Henri Becquerel discovered radiation. Along with Pierre and Marie Curie, he showed that certain elements emit energy at fixed rates. In 1903, Becquerel shared a Nobel Prize with the Curies for the discovery of radioactivity. In 1900, Max Planck discovered that energy must be emitted in discreet units that he called “quanta” (since named photons) not in continuous waves. It appeared that atoms were made up of still smaller particles, some of which could move away.

In 1911, Ernst Rutherford demonstrated that atoms consisted of a tiny dense positively charged region surrounded by relatively large areas of empty space in which still smaller, negatively charged particles (electrons) move. Rutherford assumed that the electrons orbit the nucleus in separate neat orbits, just as the planets orbit the sun. However, because the nucleus is larger and denser than the electrons, he could not explain why the electrons were not simply pulled into the nucleus thus destroying the atom.

Niels Bohr’s (1885-1962) atomic model solved this problem by using Planck’s information. Photons are emitted from an electrically stimulated atom only at certain frequencies. He hypothesized that electrons inhabit distinct energy levels and light is only emitted when an electrically “excited” electron is forced to change energy levels.

Electrons in the first energy level, closest to the nucleus, are tightly bound to the nucleus and have relatively low energy. In levels more distant from the nucleus the electrons have increasing energy. Electrons in the energy level furthest from the nucleus are not bound as tightly and are the electrons involved when atoms bond together to form compounds. The periodic nature of the elemental properties is a result of the number of electrons in the outer energy level that can be involved in chemical bonds. Although Bohr models have been replaced by more accurate atomic models, the underlying principles are sound and Bohr models are still used as simplified diagrams to show chemical bonding.

Our understanding of the atom has continued to be refined. In 1935, James Chadwick was awarded the Nobel Prize for his discovery that there are an equal number of electrically neutral particles in the nucleus of an atom. Since neutrons are electrically neutral, they are not deflected by either electrons or protons. Furthermore, neutrons have more mass than protons. These facts combine to make it possible for neutrons to penetrate atoms and break apart the nucleus, releasing vast amounts of energy. In recent years, it is increasingly obvious that the protons, neutrons and electrons of classical chemistry are made up of still smaller subatomic particles. The sciences of chemistry and physics are becoming increasingly intertwined and theories overlap and conflict as we continue to probe the materials out of which our universe is made.

Humphry Davy

Sir Humphry Davy, (17 December 1778 – 29 May 1829) was a Cornish chemist and inventor, who is best remembered today for isolating, using electricity, a series of elements for the first time: potassium and sodium in 1807 and calcium, strontium, barium, magnesium and boron the following year, as well as discovering the elemental nature of chlorine and iodine. Davy also studied the forces involved in these separations, inventing the new field of electrochemistry.

In 1799, he experimented with nitrous oxide and was astonished at how it made him laugh, so he nicknamed it "laughing gas" and wrote about its potential anaesthetic properties in relieving pain during surgery. He also invented the Davy lamp and a very early form of arc lamp. He joked that his assistant Michael Faraday was his greatest discovery.

Discovery of new elements

Davy was a pioneer in the field of electrolysis using the voltaic pile to split common compounds and thus prepare many new elements. He went on to electrolyse molten salts and discovered several new metals, including sodium and potassium, highly reactive elements known as the alkali metals. Davy discovered potassium in 1807, deriving it from caustic potash (KOH). Before the 19th century, no distinction had been made between potassium and sodium. Potassium was the first metal that was isolated by electrolysis. Davy isolated sodium in the same year by passing an electric current through molten sodium hydroxide.

Discovery of calcium, magnesium, strontium and barium

During the first half of 1808, Davy conducted a series of further electrolysis experiments on alkaline earths including lime, magnesia, strontites and barytes. At the beginning of June, Davy received a letter from the Swedish chemist Berzelius claiming that he, in conjunction with Dr. Pontin, had successfully obtained amalgams of calcium and barium by electrolysing lime and barytes using a mercury cathode. Davy managed to successfully repeat these experiments almost immediately and expanded Berzelius' method to strontites and magnesia. He noted that while these amalgams oxidized in only a few minutes when exposed to air they could be preserved for lengthy periods of time when submerged in naphtha before becoming covered with a white crust. On 30 June 1808 Davy reported to the Royal Society that he had successfully isolated four new metals which he named barium, calcium, strontium and magnesium which were subsequently published in the Philosophical Transactions. The observations gathered from these experiments also led to Davy isolating boron in 1809.

Discovery of chlorine

Chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated marine acid" and mistakenly thought it contained oxygen. Davy showed that the acid of Scheele's substance, called at the time oxymuriatic acid, contained no oxygen. This discovery overturned Lavoisier's definition of acids as compounds of oxygen. In 1810, chlorine was given its current name by Humphry Davy, who insisted that chlorine was in fact an element.The name chlorine, chosen by Davy for "one of obvious and characteristic properties - its colour", comes from the Greek χλωρος (chlōros), meaning green-yellow.

Laboratory accident

Davy seriously injured himself in a laboratory accident with nitrogen trichloride. French chemist Pierre Louis Dulong had first prepared this compound in 1811, and had lost two fingers and an eye in two separate explosions with it. In a letter to John Children, on 16 November 1812, Davy wrote: "It must be used with great caution. It is not safe to experiment upon a globule larger than a pin's head. I have been severely wounded by a piece scarcely bigger. My sight, however, I am informed, will not be injured". Davy's accident induced him to hire Michael Faraday as a co-worker, particularly for assistance with handwriting and record keeping. He had recovered from his injuries by April 1813.

Acid-base studies

In 1815 Davy suggested that acids were substances that contained replaceable hydrogen ions;– hydrogen that could be partly or totally replaced by reactive metals which are placed above hydrogen in the reactivity series. When acids reacted with metals they formed salts and hydrogen gas. Bases were substances that reacted with acids to form salts and water. These definitions worked well for most of the nineteenth century.

Alessandro Volta

Alessandro Giuseppe Antonio Anastasio Volta (18 February 1745 – 5 March 1827) was an Italian physicist, chemist, and pioneer of electricity and power who is credited as the inventor of the electric battery and the discoverer of methane. He invented the Voltaic pile in 1799, and reported the results of his experiments in 1800 in a two-part letter to the President of the Royal Society. With this invention Volta proved that electricity could be generated chemically and debunked the prevalent theory that electricity was generated solely by living beings. Volta's invention sparked a great amount of scientific excitement and led others to conduct similar experiments which eventually led to the development of the field of electrochemistry.

Volta also drew admiration from Napoleon Bonaparte for his invention, and was invited to the Institute of France to demonstrate his invention to the members of the Institute. Volta enjoyed a certain amount of closeness with the emperor throughout his life and he was conferred numerous honours by him. Volta held the chair of experimental physics at the University of Pavia for nearly 40 years and was widely idolized by his students.

Despite his professional success, Volta tended to be a person inclined towards domestic life and this was more apparent in his later years. At this time he tended to live secluded from public life and more for the sake of his family until his eventual death in 1827 from a series of illnesses which began in 1823.The SI unit of electric potential is named in his honour as the volt.

Early life and works

Volta was born in Como, a town in present-day northern Italy, on 18 February 1745. In 1794, Volta married an aristocratic lady also from Como, Teresa Peregrini, with whom he raised three sons: Zanino, Flaminio, and Luigi. His father, Filippo Volta, was of noble lineage. His mother, Donna Maddalena, came from the family of the Inzaghis.

In 1774, he became a professor of physics at the Royal School in Como. A year later, he improved and popularized the electrophorus, a device that produced static electricity. His promotion of it was so extensive that he is often credited with its invention, even though a machine operating on the same principle was described in 1762 by the Swedish experimenter Johan Wilcke. In 1777, he traveled through Switzerland. There he befriended H. B. de Saussure.

In the years between 1776 and 1778, Volta studied the chemistry of gases. He researched and discovered methane after reading a paper by Benjamin Franklin of the United States on "flammable air". In November 1776, he found methane at Lake Maggiore, and by 1778 he managed to isolate methane. He devised experiments such as the ignition of methane by an electric spark in a closed vessel.

Volta also studied what we now call electrical capacitance, developing separate means to study both electrical potential (V) and charge (Q), and discovering that for a given object, they are proportion This is called Volta's Law of Capacitance, and for this work the unit of electrical potential has been named the volt.

In 1779 he became a professor of experimental physics at the University of Pavia, a chair that he occupied for almost 40 years.

Volta and Galvani

Luigi Galvani, an Italian physicist, discovered something he named, "animal electricity" when two different metals were connected in series with a frog's leg and to one another. Volta realized that the frog's leg served as both a conductor of electricity (what we would now call an electrolyte) and as a detector of electricity. He also understood that the frog's legs were irrelevant to the electric current, which was caused by the two differing metals. He replaced the frog's leg with brine-soaked paper, and detected the flow of electricity by other means familiar to him from his previous studies. In this way he discovered the electrochemical series, and the law that the electromotive force (emf) of a galvanic cell, consisting of a pair of metal electrodes separated by electrolyte, is the difference between their two electrode potentials (thus, two identical electrodes and a common electrolyte give zero net emf). This may be called Volta's Law of the electro-chemical series.

In 1800, as the result of a professional disagreement over the galvanic response advocated by Galvani, Volta invented the voltaic pile, an early electric battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and copper. Initially he experimented with individual cells in series, each cell being a wine goblet filled with brine into which the two dissimilar electrodes were dipped. The voltaic pile replaced the goblets with cardboard soaked in brine.

Early battery

In announcing his discovery of the voltaic pile, Volta paid tribute to the influences of William Nicholson, Tiberius Cavallo, and Abraham Bennet.

The battery made by Volta is credited as one of the first electrochemical cells. It consists of two electrodes: one made of zinc, the other of copper. The electrolyte is either sulfuric acid mixed with water or a form of saltwater brine. The electrolyte exists in the form 2H+ and SO42−. The zinc, which is higher in the electrochemical series than both copper and hydrogen, reacts with the negatively charged sulfate (SO42−). The positively charged hydrogen ions (protons) capture electrons from the copper, forming bubbles of hydrogen gas, H2. This makes the zinc rod the negative electrode and the copper rod the positive electrode. Thus, there are two terminals, and an electric current will flow if they are connected. The chemical reactions in this voltaic cell are as follows:

Zinc:

Zn → Zn2+ + 2e−

Sulfuric acid:

2H+ + 2e− → H2

The copper does not react, but rather it functions as an electrode for the electric current. However, this cell also has some disadvantages. It is unsafe to handle, since sulfuric acid, even if diluted, can be hazardous. Also, the power of the cell diminishes over time because the hydrogen gas is not released. Instead, it accumulates on the surface of the copper electrode and forms a barrier between the metal and the electrolyte solution.

John Dalton

John Dalton ( 6 September 1766 – 27 July 1844) was an English chemist, physicist, and meteorologist. He is best known for introducing the atomic theory into chemistry,

John Dalton was born into Quaker family in Eaglesfield, near Cockermouth, in Cumberland, England. His father was a weaver. He received his early education from his father and from Quaker John Fletcher, who ran a private school in the nearby village of Pardshaw Hall. Dalton's family was too poor to support him for long and he began to earn his living, from the age of ten, in the service of wealthy local Quaker Elihu Robinson.

In 1787 at age 21 he began his meteorological diary in which, during the succeeding 57 years, he entered more than 200,000 observations. He rediscovered George Hadley's theory of atmospheric circulation (now known as the Hadley cell) around this time. In 1793 Dalton's first publication, Meteorological Observations and Essays, contained the seeds of several of his later discoveries but despite the originality of his treatment, little attention was paid to them by other scholars. A second work by Dalton, Elements of English Grammar (or A new system of grammatical instruction: for the use of schools and academies), was published in 1801.

He enunciated Gay-Lussac's law, published in 1802 by Joseph Louis Gay-Lussac (Gay-Lussac credited the discovery to unpublished work from the 1780s by Jacques Charles). In the two or three years following the lectures, Dalton published several papers on similar topics. "On the Absorption of Gases by Water and other Liquids" (read as a lecture on 21 October 1803, first published in 1805) contained his law of partial pressures now known as Dalton's law.

Atomic theory

The most important of all Dalton's investigations are concerned with the atomic theory in chemistry.

The essential novelty of Dalton's atomic theory is that he provided a method of calculating relative atomic weights for the chemical elements, something that neither Bryan nor William Higgins did; his priority for that crucial step is uncontested.

The main points of Dalton's atomic theory, as it eventually developed, are:

1. Elements are made of extremely small particles called atoms.
2. Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties.
3. Atoms cannot be subdivided, created or destroyed.
4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated or rearranged.

 In his first extended published discussion of the atomic theory (1808), Dalton proposed an additional (and controversial) "rule of greatest simplicity". This rule could not be independently confirmed, but some such assumption was necessary in order to propose formulas for a few simple molecules, upon which the calculation of atomic weights depended. This rule dictated that if the atoms of two different elements were known to form only a single compound, like hydrogen and oxygen forming water or hydrogen and nitrogen forming ammonia, the molecules of that compound shall be assumed to consist of one atom of each element. For elements that combined in multiple ratios, such as the then-known two oxides of carbon or the three oxides of nitrogen, their combinations were assumed to be the simplest ones possible. For example, if two such combinations are known, one must consist of an atom of each element, and the other must consist of one atom of one element and two atoms of the other.

This was merely an assumption, derived from faith in the simplicity of nature. No evidence was then available to scientists to deduce how many atoms of each element combine to form molecules. But this or some other such rule was absolutely necessary to any incipient theory, since one needed an assumed molecular formula in order to calculate relative atomic weights. Dalton's "rule of greatest simplicity" caused him to assume that the formula for water was OH and ammonia was NH, quite different from our modern understanding (H2O, NH3). On the other hand, his simplicity rule led him to propose the correct modern formulas for the two oxides of carbon (CO and CO2). Despite the uncertainty at the heart of Dalton's atomic theory, the principles of the theory survived

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Atomic weights

Dalton published his first table of relative atomic weights containing six elements (hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus), relative to the weight of an atom of hydrogen conventionally taken as 1. Since these were only relative weights, they do not have a unit of weight attached to them. Dalton provided no indication in this paper how he had arrived at these numbers, but in his laboratory notebook, dated 6 September 1803, is a list in which he set out the relative weights of the atoms of a number of elements, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time.

The extension of this idea to substances in general necessarily led him to the law of multiple proportions, and the comparison with experiment brilliantly confirmed his deduction. In the paper "On the Proportion of the Several Gases in the Atmosphere", read by him in November 1802, the law of multiple proportions appears to be anticipated in the words:

The elements of oxygen may combine with a certain portion of nitrous gas or with twice that portion, but with no intermediate quantity.

But there is reason to suspect that this sentence may have been added some time after the reading of the paper, which was not published until 1805.

Compounds were listed as binary, ternary, quaternary, etc. (molecules composed of two, three, four, etc. atoms) in the New System of Chemical Philosophy depending on the number of atoms a compound had in its simplest, empirical form.

Dalton hypothesized the structure of compounds can be represented in whole number ratios. So, one atom of element X combining with one atom of element Y is a binary compound. Furthermore, one atom of element X combining with two atoms of element Y or vice versa, is a ternary compound. Many of the first compounds listed in the New System of Chemical Philosophy correspond to modern views, although many others do not.

Dalton used his own symbols to visually represent the atomic structure of compounds. They were depicted in the New System of Chemical Philosophy, where he listed 20 elements and 17 simple molecules.

Antoine Lavoisier

It is generally accepted that Lavoisier's great accomplishments in chemistry stem largely from his changing the science from a qualitative to a quantitative one. Lavoisier is most noted for his discovery of the role oxygen plays in combustion. He recognized and named oxygen (1778) and hydrogen (1783), and opposed the phlogiston theory. Lavoisier helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He predicted the existence of silicon (1787) and was also the first to establish that sulfur was an element (1777) rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same.

The son of an attorney at the Parlement of Paris, he inherited a large fortune at the age of five upon the death of his mother. Lavoisier began his schooling at the Collège des Quatre-Nations, University of Paris (also known as the Collège Mazarin) in Paris in 1754 at the age of 11. In his last two years (1760–1761) at the school, his scientific interests were aroused, and he studied chemistry, botany, astronomy, and mathematics. In the philosophy class he came under the tutelage of Abbé Nicolas Louis de Lacaille, a distinguished mathematician and observational astronomer who imbued the young Lavoisier with an interest in meteorological observation, an enthusiasm which never left him. Lavoisier entered the school of law, where he received a bachelor's degree in 1763 and a licentiate in 1764. Lavoisier received a law degree and was admitted to the bar, but never practiced as a lawyer. However, he continued his scientific education in his spare time.

In collaboration with Guettard, Lavoisier worked on a geological survey of Alsace-Lorraine in June 1767. In 1764 he read his first paper to the French Academy of Sciences, France's most elite scientific society, on the chemical and physical properties of gypsum (hydrated calcium sulfate), and in 1766 he was awarded a gold medal by the King for an essay on the problems of urban street lighting. In 1768 Lavoisier received a provisional appointment to the Academy of Sciences.[12] In 1769, he worked on the first geological map of France.

Lavoisier consolidated his social and economic position when, in 1771 at age 28, he married Marie-Anne Pierrette Paulze, the 13-year-old daughter of a senior member of the Ferme générale.[4] She was to play an important part in Lavoisier's scientific career—notably, she translated English documents for him, including Richard Kirwan's Essay on Phlogiston and Joseph Priestley's research. In addition, she assisted him in the laboratory and created many sketches and carved engravings of the laboratory instruments used by Lavoisier and his colleagues for their scientific works. Madame Lavoisier edited and published Antoine's memoirs (whether any English translations of those memoirs have survived is unknown as of today) and hosted parties at which eminent scientists discussed ideas and problems related to chemistry.

Oxygen theory of combustion

During late 1772 Lavoisier turned his attention to the phenomenon of combustion, the topic on which he was to make his most significant contribution to science. He reported the results of his first experiments on combustion in a note to the Academy on 20 October, in which he reported that when phosphorus burned, it combined with a large quantity of air to produce acid spirit of phosphorus, and that the phosphorus increased in weight on burning. In a second sealed note deposited with the Academy a few weeks later (1 November) Lavoisier extended his observations and conclusions to the burning of sulfur and went on to add that "what is observed in the combustion of sulfur and phosphorus may well take place in the case of all substances that gain in weight by combustion and calcination: and I am persuaded that the increase in weight of metallic calces is due to the same cause."

Joseph Black's "fixed air"

During 1773 Lavoisier determined to review thoroughly the literature on air, particularly "fixed air," and to repeat many of the experiments of other workers in the field. He published an account of this review in 1774 in a book entitled Opuscules physiques et chimiques (Physical and Chemical Essays). In the course of this review he made his first full study of the work of Joseph Black, the Scottish chemist who had carried out a series of classic quantitative experiments on the mild and caustic alkalies. Black had shown that the difference between a mild alkali, for example, chalk (CaCO3), and the caustic form, for example, quicklime (CaO), lay in the fact that the former contained "fixed air," not common air fixed in the chalk, but a distinct chemical species, now understood to be carbon dioxide (CO2), which was a constituent of the atmosphere. Lavoisier recognized that Black's fixed air was identical with the air evolved when metal calces were reduced with charcoal and even suggested that the air which combined with metals on calcination and increased the weight might be Black's fixed air, that is, CO2.

Joseph Priestley

In the spring of 1774 Lavoisier carried out experiments on the calcination of tin and lead in sealed vessels, the results of which conclusively confirmed that the increase in weight of metals in combustion was due to combination with air. But the question remained about whether it was combination with common atmospheric air or with only a part of atmospheric air. In October the English chemist Joseph Priestley visited Paris, where he met Lavoisier and told him of the air which he had produced by heating the red calx of mercury with a burning glass and which had supported combustion with extreme vigor. Priestley at this time was unsure of the nature of this gas, but he felt that it was an especially pure form of common air. Lavoisier carried out his own researches on this peculiar substance. The result was his memoirOn the Nature of the Principle Which Combines with Metals during Their Calcination and Increases Their Weight, read to the Academy on 26 April 1775 (commonly referred to as the Easter Memoir). In the original memoir Lavoisier showed that the mercury calx was a true metallic calx in that it could be reduced wit charcoal, giving off Black's fixed air in the process. When reduced without charcoal, it gave off an air which supported respiration and combustion in an enhanced way. He concluded that this was just a pure form of common air, and that it was the air itself "undivided, without alteration, without decomposition" which combined with metals on calcination.

Pioneer of stoichiometry

Lavoisier's researches included some of the first truly quantitative chemical experiments. He carefully weighed the reactants and products of a chemical reaction in a sealed glass vessel so that no gases could escape, which was a crucial step in the advancement of chemistry. In 1774, he showed that, although matter can change its state in a chemical reaction, the total mass of matter is the same at the end as at the beginning of every chemical change. Thus, for instance, if a piece of wood is burned to ashes, the total mass remains unchanged if gaseous reactants and products are included. Lavoisier's experiments supported the law of conservation of mass. In France it is taught as Lavoisier's Law and is paraphrased from a statement in his Traité Élémentaire de Chimie: "Nothing is lost, nothing is created, everything is transformed." Mikhail Lomonosov (1711–1765) had previously expressed similar ideas in 1748 and proved them in experiments; others whose ideas pre-date the work of Lavoisier include Jean Rey (1583–1645), Joseph Black (1728–1799), and Henry Cavendish (1731–1810).

Chemical nomenclature

Lavoisier, together with Louis-Bernard Guyton de Morveau, Claude-Louis Berthollet, and Antoine François de Fourcroy, submitted a new program for the reforms o chemical nomenclature to the Academy in 1787, for there was virtually no rational system of chemical nomenclature at this time. This work, titled Méthode de nomenclature chimique (Method of Chemical Nomenclature, 1787), introduced a new system which was tied inextricably to Lavoisier's new oxygen theory of chemistry. The Classical elements of earth, air, fire, and water were discarded, and instead some 55 substances which could not be decomposed into simpler substances by any known chemical means were provisionally listed as elements. The elements included light; caloric (matter of heat); the principles of oxygen, hydrogen, and azote (nitrogen); carbon; sulfur; phosphorus; the yet unknown "radicals" of muriatic acid (hydrochloric acid), boric acid, and "fluoric" acid; 17 metals; 5 earths (mainly oxides of yet unknown metals such as magnesia, baria, and strontia); three alkalies (potash, soda, and ammonia); and the "radicals" of 19 organic acids. The acids, regarded in the new system as compounds of various elements with oxygen, were given names which indicated the element involved together with the degree of oxygenation of that element, for example sulfuric and sulfurous acids, phosphoric and phosphorous acids, nitric and nitrous acids, the "ic" termination indicating acids with a higher proportion of oxygen than those with the "ous" ending. Similarly, salts of the "ic" acids were given the terminal letters "ate," as in copper sulfate, whereas the salts of the "ous" acids terminated with the suffix "ite," as in copper sulfite. The total effect of the new nomenclature can be gauged by comparing the new name "copper sulfate" with the old term "vitriol of Venus." Lavoisier's new nomenclature spread throughout Europe and to the United States and became common use in the field of chemistry. This marked the beginning of the anti-phlogistic approach to the field.

Elementary Treatise of Chemistry

Lavoisier employed the new nomenclature in his Traité élémentaire de chimie (Elementary Treatise on Chemistry), published in 1789. This work represents the synthesis of Lavoisier's contribution to chemistry and can be considered the first modern textbook on the subject. The core of the work was the oxygen theory, and the work became a most effective vehicle for the transmission of the new doctrines. It presented a unified view of new theories of chemistry, contained a clear statement of the law of conservation of mass, and denied the existence of phlogiston. This text clarified the concept of an element as a substance that could not be broken down by any known method of chemical analysis, and presented Lavoisier's theory of the formation of chemical compounds from elements. It remains a classic in the history of science. While many leading chemists of the time refused to accept Lavoisier's new ideas, demand for Traité élémentaire as a textbook in Edinburgh was sufficient to merit translation into English within about a year of its French publication.mIn any event, themTraité élémentairem was sufficiently sound to convince the next generation.