Chemical Science:

Chemistry is the study of the composition, structure, and properties of matter, as well as the changes that matter undergoes during chemical reactions. It is a broad and interdisciplinary field that encompasses a wide range of topics, from the study of atoms and molecules to the development of new materials and drugs.

Here are some of the most important milestones in the history of chemistry:

• 400 BC: The Greek philosopher Aristotle proposed the theory of four elements: earth, air, fire, and water.
• 1661: The English chemist Robert Boyle published his book The Sceptical Chymist, in which he argued that all matter is composed of tiny particles called atoms.
• 1789: The French chemist Antoine Lavoisier published his book Elements of Chemistry, in which he introduced the modern system of chemical nomenclature.
• 1803: The English chemist John Dalton proposed his atomic theory, which stated that all matter is composed of atoms and that atoms of the same element are identical.
• 1828: The German chemist Friedrich Wöhler synthesized urea, a compound that was previously thought to be organic and could only be produced by living organisms. This discovery challenged the theory of vitalism, which held that living organisms were fundamentally different from non-living matter.
• 1869: The Russian chemist Dmitri Mendeleev published his periodic table of the elements, which organized the elements by their atomic weight and properties.
• 1913: The Danish physicist Niels Bohr proposed his model of the atom, which explained the structure of the atom and the emission of light by atoms.
• 1926: The Austrian physicist Erwin Schrödinger developed the Schrödinger equation, which is a mathematical equation that describes the behavior of electrons in atoms.
• 1945: The American chemist Glenn Seaborg discovered plutonium, an element that is used in nuclear weapons and nuclear power plants.
• 1953: The American scientists James Watson and Francis Crick published their paper on the structure of DNA, which is the genetic material of all living organisms.
• 1965: The American chemist Barry Sharpless developed the Sharpless asymmetric epoxidation, a chemical reaction that is used to produce chiral molecules.
• 1995: The American chemist Kary Mullis invented the polymerase chain reaction (PCR), a technique that is used to amplify DNA.
• 2005: The American chemist Roger Tsien developed the green fluorescent protein (GFP), a protein that can be used to visualize biological processes.
• 2015: The American chemist Frances Arnold was awarded the Nobel Prize in Chemistry for her work on directed evolution, a technique that is used to create new proteins with desired properties.

Antoine-Laurent de Lavoisier is often referred to as the "father of modern chemistry" due to his significant contributions to the field. Lavoisier, a French chemist, lived from 1743 to 1794 and made groundbreaking discoveries and advancements in various areas of chemistry. Here are some reasons why Lavoisier is considered a key figure in the history of chemistry:

1. Law of Conservation of Mass: Lavoisier conducted meticulous experiments to demonstrate the principle of the conservation of mass. He showed that matter is neither created nor destroyed in chemical reactions but merely rearranged. This fundamental principle laid the foundation for modern chemical stoichiometry.
2. Oxygen and Combustion: Lavoisier recognized the role of oxygen in combustion and respiration. He named the element "oxygen" and provided a clear explanation of how oxygen combines with other substances during burning. His experiments debunked the phlogiston theory, a prevailing belief at the time, and led to a better understanding of oxidation and combustion processes.
3. Chemical Nomenclature: Lavoisier played a crucial role in developing a systematic approach to chemical nomenclature. He introduced a standardized naming system for chemical elements and compounds, which simplified communication and contributed to the unification of chemical language.
4. Introduction of the Metric System: Lavoisier advocated for the adoption of a uniform system of measurement in scientific work. He was instrumental in the establishment of the metric system, which is still widely used today and provides a consistent basis for scientific measurements.
5. Chemical Analysis and Pioneering Laboratory Techniques: Lavoisier emphasized the importance of precise measurements and accurate experimental techniques in chemistry. He developed new analytical methods and improved existing ones, including the use of the balance, which allowed for accurate determination of chemical quantities.

Lavoisier's work, along with his emphasis on the importance of experimental evidence and quantitative analysis, laid the groundwork for the emergence of modern chemistry as a scientific discipline. His contributions significantly advanced our understanding of chemical reactions, elements, and compounds, and his ideas continue to influence the practice of chemistry to this day.

Chemical science has witnessed numerous milestones throughout history. Here are some notable milestones in the field of chemical science:

1. Discovery of Oxygen (1774): The English chemist Joseph Priestley discovered oxygen by isolating it in its gaseous form, recognizing its role in supporting combustion and respiration.
2. Atomic Theory (1803): John Dalton proposed the atomic theory, which laid the foundation for modern chemistry. Dalton's theory stated that elements consist of indivisible particles called atoms and that chemical reactions involve the rearrangement of atoms.
3. Periodic Law and the Periodic Table (1869): Dmitri Mendeleev developed the periodic table, organizing elements based on their atomic masses and properties. This breakthrough provided a systematic framework for understanding the relationships between elements and predicting the existence of undiscovered elements.
4. Discovery of Penicillin (1928): Alexander Fleming accidentally discovered the antibiotic properties of penicillin, marking the beginning of a new era in medicine and the development of antibiotics.
5. Quantum Mechanics (1920s): The development of quantum mechanics revolutionized the understanding of chemical behavior at the atomic and subatomic levels. Pioneers like Max Planck, Albert Einstein, Werner Heisenberg, and Erwin Schrödinger contributed to this field.
6. DNA Structure (1953): James Watson and Francis Crick proposed the double-helix structure of DNA, unraveling the molecular basis of genetic information and leading to significant advances in genetics and molecular biology.
7. Development of Polymer Science (mid-20th century): The discovery and understanding of polymers, large molecules composed of repeating subunits, opened up new possibilities for material science, engineering, and industry.
8. Green Chemistry (1990s): The concept of green chemistry emerged, focusing on the design and development of chemical processes and products that are environmentally friendly, sustainable, and minimize waste.
9. Nanotechnology (late 20th century): The field of nanotechnology involves manipulating and controlling matter at the nanoscale level. It has had a profound impact on various areas, including materials science, electronics, medicine, and energy.
10. Genome Sequencing (2000): The completion of the Human Genome Project marked a significant milestone in genetic research, enabling scientists to read the complete set of human DNA, leading to advancements in personalized medicine and our understanding of genetic diseases.

These milestones represent just a fraction of the remarkable achievements in chemical science. The field continues to evolve and contribute to our understanding of the world, leading to new discoveries, technologies, and applications.

The periodic table:

The periodic table we use today is based on the one devised and published by Dmitri Mendeleev in 1869. Mendeleev found he could arrange the 65 elements then known in a grid or table so that each element had:

1. A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0):

2. Similar chemical properties to other elements in the same column - in other words similar chemical reactions. Magnesium, for example, is placed in the alkali earths' column, with other elements whose reactions are similar:

Mendeleev realized that the table in front of him lay at the very heart of chemistry. And more than that, Mendeleev saw that his table was incomplete - there were spaces where elements should be, but no-one had discovered them.  Mendeleev could be said to have discovered germanium on paper. He called this new element eka-silicon, after observing a gap in the periodic table between silicon and tin: Similarly, Mendeleev discovered gallium (eka-aluminum) and scandium (eka-boron) on paper, because he predicted their existence and their properties before their actual discoveries.

Antonius van den Broek’s Hypothesis

In 1911 Antonius van den Broek published his hypothesis that atomic number – which at this time was simply the position of an element in the periodic table – might actually be equal to the amount of charge in the atom’s nucleus. There was, however, no experimental evidence to prove this hypothesis.

Henry Moseley

Shooting Electrons at the Elements

Moseley had learned from William and Lawrence Bragg that when high-energy electrons hit solids such as metals, the solids emit X-rays.

This intrigued Moseley, who wondered if he could study these X-rays to learn more about what goes on inside atoms; he had van den Broek’s hypothesis in mind specifically.

He moved back to Oxford in 1913. Rutherford had offered him a new fellowship at Manchester on better terms, but Moseley decided the best path for his career would be to get experience in several different laboratories. There was no fellowship open at Oxford, but Moseley believed one was coming up. He was given laboratory space but had to self-fund his work.

In a very small amount of time, he personally put together experimental apparatus to shoot high-energy electrons at different chemical elements and measure the wavelength and frequencies of the resulting X-rays.

Moseley got a straight line when he plotted the square roots of elements’ X-ray frequencies against their atomic numbers.

He discovered that each element emits X-rays at a unique frequency. He also found he could get a straight line graph by plotting the square root of X-ray frequency against elements’ atomic numbers.

Startlingly, Moseley realized that his work had confirmed van den Broek’s hypothesis.

His data made the most sense if the positive charge in the atomic nucleus increased by exactly one unit as you look from one element to the next in the periodic table. In other words, he discovered that an element’s atomic number is identical to how many protons it has.

Chemical Elements = Proton Numbers

This was enormously important. It meant Moseley had discovered that the basic difference between elements is the number of protons they have. He realized that an element is defined by its number of protons. If an element has one proton it must be hydrogen; two protons must be helium, three protons must be lithium, etc, etc. Although this may seem obvious to us today, it was a huge discovery in 1913.

Adding a proton produces a new element. Hydrogen has one proton, so its atomic number is one. Add a proton and you get helium with atomic number two. Add another proton and you get lithium with atomic number three, etc.

When Moseley arranged the elements in the periodic table by their number of protons rather than their atomic weights, the flaws in the periodic table that had been making scientists uncomfortable for decades simply disappeared.

Four New Chemical Elements

Furthermore, just like Mendeleev had done 44 years earlier, Moseley saw gaps in his new periodic table. He predicted the existence of four new elements, with 43, 61, 72, and 75 protons. These elements were discovered later by other scientists; we now call them technetium, promethium, hafnium, and rhenium.

The Periodic Table Explained at Last.

The periodic table of elements is a tabular arrangement of chemical elements based on their atomic numbers, electron configurations, and recurring chemical properties. It provides a systematic framework for organizing and understanding the properties and relationships between different elements. Here are some key features and components of the periodic table:

1. Rows (Periods): The periodic table is organized into horizontal rows called periods. There are seven periods labeled from 1 to 7. Each period signifies the filling of a new electron shell or energy level.
2. Columns (Groups/Families): The periodic table is divided into vertical columns called groups or families. Elements within the same group share similar chemical properties due to their similar electron configurations. There are 18 groups labeled from 1 to 18.
3. Element Symbols: Each element is represented by a unique chemical symbol, typically consisting of one or two letters derived from the element's name. For example, H represents hydrogen, O represents oxygen, and Fe represents iron.
4. Atomic Number: The atomic number of an element represents the number of protons in the nucleus of its atoms. It is denoted by the letter Z and determines an element's position in the periodic table. The elements are arranged in ascending order of their atomic numbers.
5. Atomic Mass: The atomic mass of an element represents the average mass of its naturally occurring isotopes. It is usually given below the element's symbol in the periodic table. The atomic mass is often expressed in atomic mass units (u) or grams per mole (g/mol).
6. Blocks: The periodic table is divided into several blocks based on the types of atomic orbitals being filled. The blocks include the s-block (Group 1 and 2), p-block (Group 13 to 18), d-block (Transition metals), and f-block (Lanthanides and Actinides).
7. Periodic Trends: The periodic table allows us to observe various trends and patterns in the properties of elements. Some notable trends include the periodic variation of atomic size (atomic radius), ionization energy, electron affinity, and electronegativity as we move across a period or down a group.
8. Main Groups: The main groups of elements in the periodic table are Group 1 (alkali metals), Group 2 (alkaline earth metals), Group 13 to 18 (p-block elements), and the noble gases (Group 18).
9. Transition Metals: The transition metals are located in the d-block of the periodic table. They exhibit typical metallic properties and are known for their variable oxidation states and the formation of complex ions.
10. Lanthanides and Actinides: The f-block elements are known as the lanthanides (from atomic number 57 to 71) and actinides (from atomic number 89 to 103). They are placed below the main body of the periodic table and are often displayed separately.

The periodic table is a powerful tool that helps scientists understand the properties, behaviors, and relationships of the elements. It continues to evolve as new elements are discovered and further research deepens our understanding of the atomic structure and chemical properties of elements.

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The Birth of Chemistry

Demons in Ore: 1742-1751

 Miners in the Harz mountains have often been frustrated by a substance that appears to be a copper ore but which, when heated, yields none of the expected metal. Even worse, it emits noxious fumes. In about 1735 Georg Brandt was able to show in his Swedish laboratory that the previously unknown substance was Cobalt. It has been identified, and Brandt gives its name to the new substance - cobalt

 A similar demon is blamed by miners in Saxony for another ore that yields a brittle substance instead of copper. The impurity in ore of this type is analyzed in Sweden in 1751 by Axel Cronstedt. He identifies its components as arsenic and a previously unknown hard white metal, quite distinct from copper. He honours the new substance and calls it nickel.

Joseph Black and fixed air: 1754-1756

1754 Joseph Black heated limestone and produced his fixed air.

Black has observed that if he heats chalk (calcium carbonate), he gets quicklime (calcium oxide) and a gas, the presence of which he can identify by its weight. Unwilling as yet to speculate on its identity, he calls it fixed air - because it exists in solid form until released.

The classic experiments of Joseph Black on magnesia alba (basic magnesium carbonate) in the 1750s; by extensive and careful use of the chemical balance, showed that an air with specific properties could combine with solid substances like quicklime and could be recovered from them.

1766-Henry Cavendish discovered inflammable gas, hydrogen.

1773-Sheele isolated oxygen using silver carbonate.

1774-Priestly discovered Oxygen by heating HgO.

Priestley and oxygen: 1774

In August 1774 Priestley directs his lens at some mercury oxide. He discovers that it gives off a colourless gas in which a candle burns with an unusually brilliant light.

In October 1774, visiting Paris with his noble patron, he describes his discovery to a gathering of French scientists. Among them is Lavoisier, who develops Priestley's experiments in his own laboratory and realizes that he has the evidence to disprove the phlogiston theory.

1775-Micro-Organisms observed using Microscope.

Lavoisier: 1777-1794

 Although Antoine Laurent Lavoisier has no single glamorous discovery to add lustre to his name (such as identifying oxygen), he is regarded as the father of modern chemistry. The reason is that during the last two decades of the 18th century, he interprets the findings of his colleagues with more scientific clarity than they have mustered, and creates the rational framework within which chemistry can develop.

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.

1778-Lavoisier named the elements, hydrogen, Oxygen, and Nitrogen. He announced that air is composed of two gases, oxygen, and nitrogen.

He explained the combustion. He concluded that during calcination, metals absorb oxygen and increase their weight.

He was able to show that Priestley's gas is involved in chemical reactions in the processes of burning and rusting and that it is transformed in both burning and breathing into the 'fixed air' discovered by Joseph Black. His research with phosphorus and sulphur caused him to believe that the new gas is invariably a component of acids. He, therefore, gives it in 1777 the name oxygen ( 'acid maker'). On a similar principle, Lavoisier coins the word hydrogen ('water maker') for the very light gas isolated by Cavendish.

 With these two names, chemistry takes a clear and decisive step into the modern era. It is an advance that Lavoisier soon consolidates.

1781-Cavendish synthesized water by burning Hydrogen in Oxygen. Cavendish mixes hydrogen and oxygen, in the proportion 2:1, in a glass globe through which he passes an electric spark. The resulting chemical reaction leaves him with water, which stands revealed as a compound (H2O).

1782-Lavoisier established the law of conservation of mass.

He said,” In a chemical  change nothing is lost and nothing is created and everything is transformed.”  He was considered the father of modern chemistry.

1789-For the first time, He Made a list of 23 known elements. He wrote the elementary treatise on chemistry. This text clarified the concept of an element as a substance that could not be broken down by any known method of chemical analysis.

1793-Alessandro Volta, an Italian Physicist, and chemist discovered the Principle of the primary battery.

In 1800, 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. Volta's method of stacking round plates of copper and zinc separated by disks of cardboard moistened with a salt solution was termed a voltaic pile. 

 Volta's invention was built on Luigi Galvani's 1780s discovery of how a circuit of two metals and a frog's leg can cause the frog's leg to respond. Volta demonstrated in 1794 that when two metals and brine-soaked cloth or cardboard are arranged in a circuit they produce an electric current. In 1800, Volta stacked several pairs of alternating copper (or silver) and zinc discs (electrodes) separated by cloth or cardboard soaked in brine (electrolyte) to increase the electrolyte conductivity. When the top and bottom contacts were connected by a wire, an electric current flowed through the voltaic pile and the connecting wire.

Thus, Volta is considered to be the founder of the discipline of electrochemistry.

 A Galvanic cell (or voltaic cell) is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell. It generally consists of two different metals connected by a salt bridge, or individual half-cells separated by a porous membrane.

 A voltaic cell is an electrochemical cell that uses a chemical reaction to produce electrical energy. The important parts of a voltaic cell: The anode is an electrode where oxidation occurs. The cathode is an electrode where reduction occurs.

 In redox reactions, electrons are transferred from one species to another. If the reaction is spontaneous, energy is released, which can then be used to do useful work. To harness this energy, the reaction must be split into two separate half-reactions: the oxidation and reduction reactions. The reactants are put into two different containers and a wire is used to drive the electrons from one side to the other. In doing so, a Voltaic/ Galvanic Cell is created.

1794- The great chemist, Lavoisier was executed in the French Revolution.

1803-Dalton's atomic theory.

Dalton 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).

1803-The law of multiple proportions by Dalton.

The law of multiple proportions is one of the basic laws of stoichiometry used to establish the atomic theory.

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.

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

1804-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.

 In chemistry, the law of definite proportion, sometimes called Proust's law or the law of definite composition, or the law of constant composition states that a given chemical compound always contains its component elements in a fixed ratio (by mass) and does not depend on its source and method of preparation.

1808- Law of combining volumes by Gay-Lussac. 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".

1811-Avogadro's law, which states that equal volumes of different gases at the same temperature and pressure must contain the same number of particles. 

Amedeo Avogadro (1776-1856), 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.

 

1812-using Volta's battery, Humphry Davy isolated new elements like, potassium, Sodium, Magnesium, Calcium, Strontium, Barium, and Boron. He went on to electrolyse molten salts and discovered several new metals, including sodium and potassium, highly reactive elements known as alkali metals. During the first half of 1808, Davy conducted a series of further electrolysis experiments on alkaline earths including lime, magnesia, strontites, and barytes.

1814-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. The observations gathered from these experiments also led to Davy isolating boron in 1809

1817-Jacob Berzelius was a Swedish Chemist.

Berzelius, [disciple of Dalton], named the elements and used symbols to represent elements in a chemical formula. He also calculated the atomic weights of different elements.

Berzelius began his career as a physician but his researches in physical chemistry were of lasting significance in the development of the subject. He is especially noted for his determination of atomic weights; his experiments led to a more complete depiction of the principles of stoichiometry, or the field of chemical combining proportions. In 1803 Berzelius demonstrated the power of an electrochemical cell to decompose chemicals into pairs of electrically opposite constituents.

Berzelius's work with atomic weights and his theory of electrochemical dualism led to his development of a modern system of chemical formula notation that could portray the composition of any compound both qualitatively (by showing its electrochemically opposing ingredients) and quantitatively (by showing the proportions in which the ingredients were united). His system abbreviated the Latin names of the elements with one or two letters and applied subscripts to designate the number of atoms of each element present in both the acidic and basic ingredients

1834-Michael Faraday

Faraday discovered that when electricity is passed through ionic solutions, the amount of chemical change produced was proportional to the quantity of electricity passed through it.

Electrochemistry is a branch of chemistry concerned with the relation between electricity and chemical change. Many spontaneously occurring chemical reactions liberate electrical energy, and some of these reactions are used in batteries and fuel cells to produce electric power. Conversely, electric current can be utilized to bring about many chemical reactions that do not occur spontaneously. In the process called electrolysis, electrical energy is converted directly into chemical energy, which is stored in the products of the reaction. This process is applied in refining metals, electroplating, and in producing hydrogen and oxygen from water.

An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy. They are often used to decompose chemical compounds, in a process called electrolysis—the Greek word lysis means to break up.

An electrolytic cell has three component parts: an electrolyte and two electrodes (a cathode and an anode). The electrolyte is usually a solution of water or other solvents in which ions are dissolved.

 

Faraday's law states that “the amount of any substance deposited or liberated during electrolysis is proportional to the quantity of electric charge passed and to the equivalent weight of the substance.” 

Faraday's First Law of Electrolysis. The mass of the substance (m) deposited or liberated at any electrode is directly proportional to the quantity of electricity or charge (Q) passed. Faraday further observed that 1 Faraday (96,485C) of charge liberates 1 gram equivalent of the substance at the electrodes.

Faraday’s First Law of Electrolysis states that the chemical deposition due to the flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.

  Faraday’s second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.

Chemical Equivalent or Equivalent Weight

The chemical equivalent or equivalent weight of a substance can be determined by Faraday’s laws of electrolysis, and it is defined as the weight of that substance which will combine with or displace the unit weight of hydrogen.
The chemical equivalent of hydrogen is, thus, unity. Since the valency of a substance is equal to the number of hydrogen atoms, which it can replace or with which it can combine, the chemical equivalent of a substance, therefore may be defined as the ratio of its atomic weight to its valency.

In 1841, the chemical society of London was founded in England by 77 scientists as a result of increased interest in scientific matters. Chemist Robert Warrington was the driving force behind its creation. The Chemical Society of London is a "fruitful amalgamation of the technological and academic chemists". 1845-the Royal College of Chemistry was founded.

1851-The Royal School of Mines was established in London

 

1852-concept of valency by Edward Frankland.

Research beginning about 1850 led him to the idea that an atom of an element can combine only with a certain limited number of atoms of other elements. He thus established a theory of valency (1852), which became the basis of modern structural chemistry.

In 1866 he published an influential textbook, Lecture Notes, in which he adopted Crum Brown’s graphic (structural) formulas and argued (against Kekulé) that elements could exhibit more than one valence below a fixed upper maximum. 

 From 1863 to 1870 he and Baldwin Duppa exploited zinc ethyl and other organic reagents, including ethyl acetate, in the synthesis of ethers, dicarboxylic acids, unsaturated monocarboxylic acids, and hydroxy acids. This meticulous work revealed clearly the structure and relationship of these compounds, and of course, its methodology had a great bearing on the growth of the chemical industry.

Reagents are "substances or compounds that are added to a system in order to bring about a chemical reaction or are added to see if a reaction occurs. 

In1860-world's first chemical conference was held in Europe [Karlsruhe Congress] by Kekule.140 delegates participated in it. The young Siberian Mendeleyev was also present in the meeting.

 An important long-term result of the Karlsruhe Congress was the adoption of the now-familiar atomic weights.

Prior to the Karlsruhe meeting, and going back to Dalton's work in 1803, several systems of atomic weights were in use. In one case, a value of 1 was adopted as the weight of hydrogen (the base unit), with 6 for carbon and 8 for oxygen. As long as there were uncertainties over atomic weights then the compositions of many compounds remained in doubt. Following the Karlsruhe meeting, values of about 1 for hydrogen, 12 for carbon, 16 for oxygen, and so forth were adopted. This was based on the recognition that certain elements, such as hydrogen,  nitrogen, and oxygen, were composed of diatomic molecules and not individual atoms.

Rocke says. “If you believed Avogadro’s theory, then you could get the correct molecular formula for molecules, as well as the correct atomic weights, which was the groundwork required to construct the periodic table,“ he says.

When the 1860 conference began, the chemistry was in a total state of disarray.

Participants broke into groups to discuss contentious issues, such as stoichiometry or representation of molecular formulas, and then they would return to the plenary hall to share their deliberations, Podlech says. However, sometimes a group’s consensus was undermined by the presenter’s personal opinions

In fact, the conference was mostly dominated by voices from the old guard—so much so that the organizers began to fear their efforts were in vain and that the conference was going to be a complete failure. But just before the meeting’s close, a relatively unknown Italian chemist named Stanislao Cannizzaro gave a long, impassioned, and eloquent lecture that argued for Avogadro’s perspective on molecules. After Cannizzaro’s lecture, one of his friends handed out a paper that effectively reiterated his speech and that several important delegates read on their trips home.

“It was as though the scales fell from my eyes; doubt vanished, and it was replaced by a feeling of peaceful certainty,“ wrote Meyer, who would later go on to construct a correct periodic table around the same time as Mendeleev put his together. Mendeleev wrote that the meeting “produced such a remarkable effect on the history of our science that I consider it a duty ... to describe all the sessions ... and the results.“

But Cannizzaro’s plea needed some time to sink in, and it took about a decade before scientists hashed out the correct molecular weights that enabled the periodic table to emerge. “On that last day in Karlsruhe, there were no cheers, no sudden enlightenment, no ovation,” Rocke notes. “The assembled chemists simply quietly filed out of the hall and went home.

The Karlsruhe meeting was the first international meeting of chemists and it led to the eventual founding of the International Union of Pure and Applied Chemistry (IUPAC).

Later, German chemist Lothar Meyer, and the Russian chemist Dmitri Mendeleev, who had both been in attendance at Karlsruhe, constructed element arrangements using the Cannizzaro numbers - on tables: with the elements arranged in rows and columns - for schoolbooks. 

In1869-Mendeleyev constructed the periodic table of elements, based on increasing atomic weights of elements.

1898-discovery of Nobel gases by William Ramsay.

 

Antoine Lavoisier:

Antoine Lavoisier (1743-1794) is often called the father of modern chemistry. He is possibly the greatest scientist France ever produced. The son of a wealthy Parisian lawyer, Lavoisier completed a law degree to please his parents, but his real interest was in science. In 1768 he was elected to the prestigious French Academy of Sciences in which he was a rising star, becoming director in 1785.

Peter Atkins, the noted UK chemist, credits Lavoisier as "The Father of Modern Chemistry" for three reasons.

First, Lavoisier introduced a new language of chemistry, which swept away the old terminology based on the natural origins of things, such as flowers and trees - terminologies that said nothing about the chemical composition of the material.

Second, Lavoisier emphasized the fundamental distinction between elements and compounds and established the basic rules of chemical combination. One of his most famous experiments was a public demonstration that water is made up of the two elements, hydrogen and oxygen.

Third, Lavoisier introduced precise measurement into chemistry and so turned it into an exact physical science.

Lavoisier is best remembered for overturning the theory of phlogiston.

Phlogiston was a hypothetical substance, postulated in the 17th century to explain combustion. The theory held that combustible substances contain phlogiston and combustion is essentially the process of losing phlogiston.

The British chemist Joseph Priestley (1733-1804) discovered that air is composed of several gases, one of which is essential to animal life, which Priestley called "dephlogisticated air". He generated it by heating mercuric oxide and collecting the gas that was given off. Priestley showed Lavoisier how to make dephlogisticated air.

Lavoisier re-named dephlogisticated air as oxygen. The emanation of oxygen from mercuric oxide suggested to Lavoisier that chemical decomposition could be quantified. He ran the experiment in both directions. First he burned mercury in oxygen and measured the amount of oxygen that combines with the mercury to make mercuric oxide.

Next he took the mercuric oxide and heated it to expel the oxygen, leaving mercury behind. When he measured the oxygen generated, it was exactly the amount that had been taken up before.

The overall process was revealed as the combination and uncoupling of fixed quantities of mercury and oxygen. Combustion of mercury was revealed as chemical combination with oxygen and therefore, phlogiston was no more. 

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 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 the 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

Joseph Priestley, an English chemist known for isolating oxygen, which he termed "dephlogisticated air."

In the spring of 1774 Lavoisier carried out experiments on the calcination of tin and lead in sealed vessels 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 that released air 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 famous memoir On the Nature of the Principle Which Combines with Metals during Their Calcination and Increases Their Weight, read to the Academy on 26 April 1775. In the original memoir Lavoisier showed that the mercury calx was a true metallic calx in that it could be reduced with 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.
After returning from Paris, Priestley took up once again his investigation of the air from mercury calx. His results now showed that this air was not just an especially pure form of common air but was "five or six times better than common air, for the purpose of respiration, inflammation, and ... every other use of common air." He called the air dephlogisticated air, as he thought it was common air deprived of its phlogiston. Since it was therefore in a state to absorb a much greater quantity of phlogiston given off by burning bodies and respiring animals, the greatly enhanced combustion of substances and the greater ease of breathing in this air were explained.

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 "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).