chemistry

Branch of science concerned with the study of the structure and composition of the different kinds of matter, the changes that matter may undergo, and the phenomena which occur in the course of these changes.

Organic chemistry is the branch of chemistry that deals with carbon compounds. Inorganic chemistry deals with the description, properties, reactions, and preparation of all the elements and their compounds, with the exception of carbon compounds. Physical chemistry is concerned with the quantitative explanation of chemical phenomena and reactions, and the measurement of data required for such explanations. This branch studies in particular the movement of molecules and the effects of temperature and pressure, often with regard to gases and liquids.

Atoms, molecules, and elements
All matter can exist in three states: gas, liquid, or solid. It is composed of minute particles called atoms which are constantly moving. Atoms may be joined together by covalent bonds to form molecules, which may contain only two (such as oxygen and nitrogen) or up to hundreds of thousands (such as DNA and proteins) of atoms.

A specific type of atom, as identified by its chemical properties, represents a chemical element. All elements are classified in the periodic table of the elements, developed by English chemist John Newlands in 1863 and established by Russian chemist Dmitri Mendeleyev in 1869. At first, it classified elements according to their relative atomic masses. Those elements that resemble each other in general properties were found to bear a relation to one another by weight, and these were placed in groups or families. Certain anomalies in this system were later removed by classifying the elements according to their atomic numbers. The latter is equivalent to the positive charge on the nucleus of the atom. A specific type of atom, as identified by the number of protons it contains, represents a chemical element. All elements are classified in the periodic table of the elements.

Elements are divided into metals, which have lustre and conduct heat and electricity, and nonmetals, which usually lack these properties.

Compounds and mixtures
A substance whose molecules contain different elements is a compound. Chemical compounds are produced by a chemical action that alters the arrangement of the atoms in the reacting molecules. Heat, light, vibration, catalytic action, radiation, or pressure, as well as moisture (for ionization), may be necessary to produce a chemical change. Examination and possible breakdown of compounds to determine their components is analysis, and the building up of compounds from their components is synthesis. When substances are brought together without changing their molecular structures they are said to be mixtures.

Formulas and equations
Symbols are used to denote the elements. The symbol is usually the first letter or letters of the English or Latin name of the element – for example, C for carbon; Ca for calcium; Fe for iron (ferrum). These symbols represent one atom of the element; molecules containing more than one atom of an element are denoted by a subscript figure – for example, water is H₂O. In some substances a group of atoms acts as a single entity, and these are enclosed in parentheses in the symbol – for example (NH₄)₂SO₄ denotes ammonium sulphate. The symbolic representation of a molecule is known as a formula. A figure placed before a formula represents the number of molecules of a substance taking part in, or being produced by, a chemical reaction – for example, 2H₂O indicates two molecules of water. Chemical reactions are expressed by means of equations as in:

NaCl + H₂SO₄ → NaHSO₄ + HCl

This equation states the fact that sodium chloride (NaCl) on being treated with sulphuric acid (H₂SO₄) is converted into sodium bisulphate (sodium hydrogen sulphate, NaHSO₄) and hydrogen chloride (HCl). See also chemical equation.

Alchemy
Ancient civilizations were familiar with certain chemical processes – for example, extracting metals from their ores, and making alloys. The alchemists endeavoured to turn base (nonprecious) metals into gold, and chemistry evolved towards the end of the 17th century from the techniques and insights developed during alchemical experiments.

Landmarks in chemistry
Robert Boyle defined elements as the simplest substances into which matter could be resolved. The alchemical doctrine of the four elements (earth, air, fire, and water) gradually lost its hold, and the theory that all combustible bodies contain a substance called phlogiston (a weightless ‘fire element’ generated during combustion) was discredited in the 18th century by the experimental work of Joseph Black, Antoine Lavoisier, and Joseph Priestley (who discovered the presence of oxygen in air).

Henry Cavendish discovered the composition of water, and John Dalton put forward the atomic theory, which ascribed a precise relative weight to the ‘simple atom’ characteristic of each element.

In the 19th century, synthetic dyes were discovered and their production became the foundation of the chemical industry. Numerous new elements and syntheses were discovered. Friedrich Wöhler's synthesis of urea in 1828 is often considered the birth of organic chemistry. Robert Brown discovered in 1827 the random thermal motion of molecules now known as Brownian motion. In 1848 Louis Pasteur made the discovery that certain molecules occur in two versions, which are mirror images of each other. Friedrich August Kekulé von Stradonitz realized in 1865 that carbon must be tetravalent and that alternating double and single bonds can account for the structure of benzene. Josiah W Gibbs stated some of the fundamental laws of thermodynamics, which became the foundation of physical chemistry.

In the 20th century, the new chemical disciplines such as polymer chemistry (leading to the production of a wide range of plastics, biochemistry, medicinal chemistry (see chemotherapy), quantum chemistry, and electrochemistry became increasingly important. The periodic table was expanded by the synthesis of new elements. New analytical methods have enabled chemists to investigate chemical processes at the level of single molecules. Many new materials developed by chemists replaced traditional materials in the production of consumer goods. Chemically produced fertilizers and s have had a huge impact on the food supply all over the world.

chemistry - events

297	China	The tomb of a Chinese military commander of this date contains metal belt ornaments made of aluminium, not isolated by Western scientists until 1827.
c. 1313	Germany	German Grey Friar Berthold der Schwarze is traditionally credited with the independent invention of gunpowder. He is also acknowledged as the first European to cast a bronze cannon.
1610	France	French chemist Jean Beguin publishes Tyrocinium chymicum/An introduction to chemistry, the first textbook on chemistry rather than alchemy.
1665	Ireland	Using vacuum pumps, Anglo-Irish chemist and physicist Robert Boyle proves that air is necessary for candles to burn and for animals to live.
1666	Germany	The German chemist Otto Tachenius publishes his Hippocrates chimicus/Chemistry of Hippocrates, proposing that all salts arise from the combination of an acid with a base.
1670	Ireland	Anglo-Irish chemist and physicist Robert Boyle discovers hydrogen (atomic number 1), produced when certain metals react with acid, although he does not identify it as an element.
1723	Germany	Georg Ernst Stahl develops his phlogiston theory and discusses its concepts in his Fundamenta Chemiae Dogmaticae et Experimertalis. He theorizes that all combustible substances contain a material called phlogiston, which escapes during burning and is replaced by contact with combustible materials.
1742	Sweden	Swedish scientist Anders Celsius proposes an international fixed temperature scale to the Swedish Academy of Sciences, with 100° set as the freezing point of water, and 0° set as the boiling point; this is later reversed.
1755	Scotland	Scottish chemist Joseph Black identifies carbon dioxide, which he calls ‘fixed air’.
1766	England	English scientist Henry Cavendish discovers the element hydrogen (atomic number 1) and delivers papers to the Royal Society of London, England, on the chemistry of gases.
1 November 1772	France	French chemist Antoine-Laurent Lavoisier disproves the phlogiston theory by demonstrating that combustion is caused by a reaction with a component of air.
1774	France	French chemist Antoine-Laurent Lavoisier demonstrates the conservation of mass in chemical reactions.
1 August 1774	England	English chemist Joseph Priestley discovers the element oxygen (atomic number 8).
1777	France	French chemist Antoine-Laurent Lavoisier presents his ‘Memoir’ paper to the French Academy of Sciences in which he refutes the phlogiston theory of combustion and forwards the idea oxygen-based combustion.
1777	Sweden	Swedish chemist Karl Scheele discovers that silver nitrate, when exposed to light, results in a blackening effect. This is an important discovery for the development of photography.
1784	England	English chemist and physicist Henry Cavendish discovers that water is a compound of hydrogen and oxygen.
1787	France	French chemist Antoine-Laurent Lavoisier, with collaborators, publishes Méthode de nomenclature chimie/Method of Chemical Nomenclature, a system for naming chemicals based on scientific principles.
1790	France	French chemist Nicolas Leblanc invents an inexpensive process for the manufacture of soda (sodium hydroxide and sodium carbonate) from salt (sodium chloride). This leads to the development of the soap industry in France and provides raw materials for the glass, porcelain, and paper-pulp industries.
1801	England	English chemist and physicist John Dalton formulates the law of partial pressure of gases.
1802	France	French chemist and physicist Joseph Louis Gay-Lussac demonstrates that all gases expand by the same fraction of their volume when their temperature is increased by the same amount.
1803	England	English chemist and physicist John Dalton proposes his atomic theory of matter. He revives the theory put forward by the Greek philosopher Democritus (460–370 BC) that elements are made up of minute indestructible particles, called atoms.
31 December 1808	France	French chemist Joseph-Louis Gay-Lussac publishes The Combination of Gases, in which he announces that gases combine chemically in simple proportions of volumes.
1813	Sweden	Swedish chemist Jöns Jakob Berzelius introduces the modern system of chemical symbols.
1814	Sweden	Swedish chemist Jöns Jakob Berzelius publishes his An Attempt to Establish a Pure Scientific System of Mineralogy through the Use of the Electrochemical Theory of Chemical Proportions, an extensive chemical classification of minerals in which he classifies over two thousand chemical compounds.
1828	Germany	German chemist Friedrich Wöhler synthesizes urea from ammonium cyanate. It is the first synthesis of an organic substance from an inorganic compound.
1837	Germany	German chemist Karl Friedrich Mohr enunciates the theory of conservation of energy.
1846	Italy	Italian chemist Ascanio Sobrero is the first to prepare the powerful explosive nitroglycerine.
1854	France	French scientist Henri-Etienne Sainte-Claire Deville develops a new process for making aluminium.
1855	UK	British chemist Alexander Parkes invents the first synthetic plastic.
1858	England	English chemists William Henry Perkin and B F Duppa synthesize the amino acid, glycine.
1858	Germany	German chemist Friedrich Kekulé von Stradonitz publishes Uber die Konstitution und die Metamorphosen der chemischen Verbindungen and über die chemische Natur des Kohlenstoffs/On the Constitution and Changes of Chemical Compounds and on the Chemical Nature of Carbon, in which he shows that carbon atoms can link together to form long chains, the basis of organic molecules.
1861	Belgium	Belgian chemist Ernest Solvay patents a method for the economic production of sodium carbonate, washing soda, from sodium chloride, ammonia, and carbon dioxide.
1863	England	English chemist John Alexander Reina Newlands devises the table of the elements.
1865	Germany	German chemist Friedrich August Kekulé von Stradonitz proposes the molecular structure of benzene.
1867	Sweden	Swedish chemist Alfred Bernhard Nobel patents the blasting explosive dynamite.
1869	Russia	Russian chemist Dmitry Ivanovich Mendeleyev develops the periodic table of the elements. He leaves gaps for elements yet to be discovered.
1869	USA	US inventor John Wesley Hyatt, in an effort to find a substitute for the ivory in billiard balls, invents celluloid. The first artificial plastic, it can be produced cheaply in a variety of colours, is resistant to water, oil, and weak acids, and quickly finds use in making such things as combs, toys, and false teeth.
1874	Netherlands, France	The Dutch chemist Jacobus Henricus van't Hoff and the French chemist Joseph-Achile Le Bel, independently propose a three-dimensional shape for organic molecules based on a tetrahedral carbon atom.
1879	USA	US chemist Ira Remsen and his German student Constantin Fahlberg discover the artificial sweetener saccharin; it is 500 times sweeter than sugar.
1886	Sweden	Swedish chemist Svante August Arrhenius introduces the idea that acids are substances that dissociate in water to yield hydrogen ions, H⁺, and that bases are substances that dissociate to yield hydroxide ions, OH^-.
1886	USA	US chemist Charles Martin Hall and French chemist Paul-Louis-Toussaint Héroult independently develop the same method for the production of aluminium by the electrolysis of aluminium oxide.
1892	France	French chemist Ferdinand-Frédéric Henri Moissan invents the first electric-arc furnace. He uses it to create many new compounds and to vaporize substances that had been considered to be impossible to melt.
1898	France	French chemists Pierre Curie and Marie Curie discover the radioactive elements polonium (atomic number 84) and radium (atomic number 88). Radium is discovered in pitchblende and is the first element to be discovered radiochemically.
1899	Germany	German chemist Emil Fischer postulates the ‘lock and key’ hypothesis to explain the specificity of enzyme action.
1906	Russian Empire	Russian botanist Mikhail Semyonovich Tsvet develops chromatography to separate plant pigments.
1909		Danish biochemist Søren Peer Lauritz Sørensen devises the pH scale for measuring acidity and alkalinity.
1913		English physicist Henry Gwyn-Jeffreys Moseley discovers the characteristic feature of an element, the atomic number. Moseley discovers that the X-ray spectra of the elements have a deviation that changes regularly through the periodic table.
1925	Austria	Austrian physicist Wolfgang Pauli discovers the exclusion principle, which accounts for the electronic structure of the atom and the chemical properties of the elements. Pauli's exclusion principle states that no two electrons can occupy the same state or configuration, which relates quantum theory to the observed properties of atoms.
1926	Germany	German chemist Hermann Staudinger proves that polymers are formed by chemical interaction between small monomer units.
1930		Swedish biochemist Arne Wilhem Kaurin Tiselius invents electrophoresis. This process, also known as ‘cataphoresis’, is defined as the movement of electrically charged particles through a liquid under the influence of an applied electric field.
1934	France	French physicists Frédéric and Irène Joliot-Curie bombard boron, aluminium, and magnesium with alpha particles and obtain radioactive isotopes of nitrogen, phosphorus, and aluminium – elements that are not normally radioactive. They are the first radioactive elements to be prepared artificially.
1937	Germany, UK	German-born British biochemist Hans Adolf Krebs describes the citric acid cycle in cells, which converts sugars, fats, and proteins into carbon dioxide, water, and energy – the ‘Krebs cycle’.
1944	USA	The role of deoxyribonucleic acid (DNA) in genetic inheritance is first demonstrated by US bacteriologist Oswald Theodore Avery, US biologist Colin M MacLeod, and US biologist Maclyn McCarthy.
1944	UK	British biochemists Archer John Porter Martin and Richard Laurence Millington Synge invent paper chromatography.
1946	USA	The US physicists Edward Mills Purcell and Felix Bloch independently discover nuclear magnetic resonance, which is used to study the structure of pure metals and composites.
1951	USA	US chemists Linus Pauling and Robert Corey establish the helical or spiral structure of proteins.
1952	UK	British biochemists Archer Martin and Anthony T James develop gas chromatography, a technique for separating the elements of a gaseous compound.
28 August 1976	USA	Indian-born US biochemist Har Gobind Khorana and his colleagues announce the construction of the first artificial gene to function naturally when inserted into a bacterial cell.
April 1983	USA	US biochemist Kary Banks Mullis invents the polymerase chain reaction (PCR). This is a method of copying genes or known sections of a DNA molecule a million times without the need for a living cell.
1985	England	English chemist Harold Walter Kroto and US chemists Robert Floyd Curl and Richard Erret Smalley discover fullerenes.
1988	USA	Researchers at IBM's Almaden Research Center in San José, California, using a scanning tunnelling microscope, produce the first image of the ring structure of benzene, the simplest aromatic hydrocarbon. The image confirms the structure of the molecule envisioned by Frederick Kekulé in 1865.
March 1999	Russia	Russian scientists at the Joint Institute for Nuclear Research at Dubna create ununquadium (atomic number 114).

chemistry (redirected from Chemics)

chemistry

Atoms, molecules, and elements

Compounds and mixtures

Formulas and equations

Alchemy

Landmarks in chemistry

chemistry - events

chemistry
(redirected from Chemics)