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Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during reactions with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds.

In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth ( botany), the formation of igneous rocks ( geology), how atmospheric ozone is formed and how environmental pollutants are degraded ( ecology), the properties of the soil on the moon ( cosmochemistry), how medications work ( pharmacology), and how to collect DNA evidence at a crime scene ( forensics).

Chemistry has existed under various names since ancient times. Over this time frame, it has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. The applications of various fields of chemistry are used frequently for economic purposes in the chemical industry. ( Full article...)

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Coffee beans; a coffee bean contains between 0.8 - 2.5% caffeine.
Caffeine is a xanthine alkaloid compound that acts as a stimulant in humans. Caffeine is sometimes called guaranine when found in guarana, mateine when found in mate, and theine when found in tea. It is found in the leaves and beans of the coffee plant, in tea, yerba mate, and guarana berries, and in small quantities in cocoa, the kola nut and the Yaupon Holly. Overall, caffeine is found in the beans, leaves, and fruit of over 60 plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding upon them.

Caffeine is a central nervous system (CNS) stimulant, having the effect of temporarily warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks enjoy great popularity: caffeine is the world's most widely consumed psychoactive substance. In North America, 90% of adults consume caffeine daily.

Many natural sources of caffeine also contain widely varying mixtures of other xanthine alkaloids, including the cardiac stimulants theophylline and theobromine and other substances such as tannins.


History and Philosophy of Chemistry

Antoine Lavoisier
Antoine Lavoisier

Many chemists have an interest in the history of chemistry. Those with philosophical interests will be interested that the philosophy of chemistry has quite recently developed along a path somewhat different from the general philosophy of science.

Other articles that might interest you are:

There is a Wikipedia Project on the History of Science.

Chemistry Resources

Wikipedia:WikiProject Chemicals/Data is a collection of links and references that are useful for chemistry-related works. This includes free online chemical databases, publications, patents, computer programs, and various tools. A good place to figure out what equals what.

General Chemistry Online Clear text and comprehensive coverage of general chemistry topics by Fred Senese, Dept. of Chemistry Frostburg State University

General Chemistry Demonstration at Purdue Video clips (and descriptions) of lecture demonstrations.

Chemistry Webercises Directory A large listing of chemistry resources maintained by Steven Murov, Emeritus Chemistry Professor Modesto Junior College.

MathMol MathMol (Mathematics and Molecules) is a good starting point for those interested in the field of molecular modeling.

ABC-Chemistry A directory of free full-text journals in chemistry, biochemistry and related subjects.

The Element Song A goofy little song about all of the elements.

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Paclitaxel is an important drug used for the treatment of cancer. Its complex structure provided a challenging target for its total synthesis by the Nicolaou group. The colors indicate the approach they used.

Selected biography

Hermann Emil Fischer
Hermann Emil Fischer (1852-1919) was a German chemist, and recipient of the Nobel Prize for Chemistry in 1902. Many consider Fischer to be the most brilliant chemist who ever lived, because of his numerous contributions to science, especially chemistry and biochemistry. Among these is his discovery of phenylhydrazine. He also undertook vast studies on purines. This work showed that various substances such as adenine, xanthine, caffeine, uric acid, and guanine, all belonged to one homogeneous family, and could be derived from one another. He reasoned this to be due to their common origins from a parent molecule, a bicyclic nitrogenous structure into which the characteristic urea group entered. Fischer regarded this structure as hypothetical, and named it 'purine' in 1884. He synthesised it in 1898. He is also famed for his work on sugars.

Techniques used by chemists

Equipment used by chemists

Chemistry in society

Chemistry in industry



Periodic Table

Group 1 2   3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Hydrogen &
alkali metals
Alkaline earth metals Triels Tetrels Pnicto­gens Chal­co­gens Halo­gens Noble


Hydro­gen1H1.0080 He­lium2He4.0026
2 Lith­ium3Li6.94 Beryl­lium4Be9.0122 Boron5B10.81 Carbon6C12.011 Nitro­gen7N14.007 Oxy­gen8O15.999 Fluor­ine9F18.998 Neon10Ne20.180
3 So­dium11Na22.990 Magne­sium12Mg24.305 Alumin­ium13Al26.982 Sili­con14Si28.085 Phos­phorus15P30.974 Sulfur16S32.06 Chlor­ine17Cl35.45 Argon18Ar39.95
4 Potas­sium19K39.098 Cal­cium20Ca40.078 Scan­dium21Sc44.956 Tita­nium22Ti47.867 Vana­dium23V50.942 Chrom­ium24Cr51.996 Manga­nese25Mn54.938 Iron26Fe55.845 Cobalt27Co58.933 Nickel28Ni58.693 Copper29Cu63.546 Zinc30Zn65.38 Gallium31Ga69.723 Germa­nium32Ge72.630 Arsenic33As74.922 Sele­nium34Se78.971 Bromine35Br79.904 Kryp­ton36Kr83.798
5 Rubid­ium37Rb85.468 Stront­ium38Sr87.62 Yttrium39Y88.906 Zirco­nium40Zr91.224 Nio­bium41Nb92.906 Molyb­denum42Mo95.95 Tech­netium43Tc​[97] Ruthe­nium44Ru101.07 Rho­dium45Rh102.91 Pallad­ium46Pd106.42 Silver47Ag107.87 Cad­mium48Cd112.41 Indium49In114.82 Tin50Sn118.71 Anti­mony51Sb121.76 Tellur­ium52Te127.60 Iodine53I126.90 Xenon54Xe131.29
6 Cae­sium55Cs132.91 Ba­rium56Ba137.33 1 asterisk Lute­tium71Lu174.97 Haf­nium72Hf178.49 Tanta­lum73Ta180.95 Tung­sten74W183.84 Rhe­nium75Re186.21 Os­mium76Os190.23 Iridium77Ir192.22 Plat­inum78Pt195.08 Gold79Au196.97 Mer­cury80Hg200.59 Thallium81Tl204.38 Lead82Pb207.2 Bis­muth83Bi208.98 Polo­nium84Po​[209] Asta­tine85At​[210] Radon86Rn​[222]
7 Fran­cium87Fr​[223] Ra­dium88Ra​[226] 1 asterisk Lawren­cium103Lr​[266] Ruther­fordium104Rf​[267] Dub­nium105Db​[268] Sea­borgium106Sg​[269] Bohr­ium107Bh​[270] Has­sium108Hs​[269] Meit­nerium109Mt​[278] Darm­stadtium110Ds​[281] Roent­genium111Rg​[282] Coper­nicium112Cn​[285] Nihon­ium113Nh​[286] Flerov­ium114Fl​[289] Moscov­ium115Mc​[290] Liver­morium116Lv​[293] Tenness­ine117Ts​[294] Oga­nesson118Og​[294]
1 asterisk Lan­thanum57La138.91 Cerium58Ce140.12 Praseo­dymium59Pr140.91 Neo­dymium60Nd144.24 Prome­thium61Pm​[145] Sama­rium62Sm150.36 Europ­ium63Eu151.96 Gadolin­ium64Gd157.25 Ter­bium65Tb158.93 Dyspro­sium66Dy162.50 Hol­mium67Ho164.93 Erbium68Er167.26 Thulium69Tm168.93 Ytter­bium70Yb173.05  
1 asterisk Actin­ium89Ac​[227] Thor­ium90Th232.04 Protac­tinium91Pa231.04 Ura­nium92U238.03 Neptu­nium93Np​[237] Pluto­nium94Pu​[244] Ameri­cium95Am​[243] Curium96Cm​[247] Berkel­ium97Bk​[247] Califor­nium98Cf​[251] Einstei­nium99Es​[252] Fer­mium100Fm​[257] Mende­levium101Md​[258] Nobel­ium102No​[259]

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  1. ^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi: 10.1515/pac-2015-0305.
  2. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi: 10.1515/pac-2019-0603. ISSN  1365-3075.
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