An oil painting of a chemist (by Henrika Šantel in 1932).
Chemistry is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.
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 chemistry (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 (astrophysics), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics).
Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron(s); ionic bonds, in which a compound donates one or more electrons to another compound to produce ions (cations and anions); hydrogen bonds; and Van der Waals force bonds.
that slow or prevent the oxidation
of other chemicals
. Oxidation is a redox chemical reaction
that transfers electrons
from a substance to an oxidizing agent
. Oxidation reactions can involve the production of free radicals
, which can form dangerous chain reactions
. Antioxidants can terminate these chain reactions by removing radical intermediates and can inhibit other oxidation reactions by being oxidized themselves. As a result, antioxidants are often reducing agents
such as thiols
Although oxidation reactions are critical for life, they can also be damaging; hence, plants and animals maintain complex systems of multiple types of antioxidants, such as glutathione, vitamin C, and vitamin E as well as enzymes such as catalase, superoxide dismutase and various peroxidases. Low levels of antioxidant molecules or inhibition of these antioxidant enzymes causes oxidative stress and may damage or kill cells.
As oxidative stress has been implicated in the pathogenesis of many human diseases, the use of antioxidants in pharmacology is intensively studied, particularly as treatments for stroke and neurodegenerative diseases. Antioxidants are also widely used as ingredients in dietary supplements in the hope of maintaining health and preventing diseases such as cancer and coronary heart disease. In addition to these uses in medicine, antioxidants have many industrial uses, such as preservatives in food and cosmetics and preventing the degradation of rubber and gasoline.
History and Philosophy of Chemistry
(1893-1981) was an American physical chemist
, who won the 1934 Nobel Prize in Chemistry
for his work on isotopes
, specifically the discovery of deuterium
, a hydrogen
isotope, and the production of heavy water
. He also performed pioneering research in cosmochemistry
, which studies the origin and development of elements
and their isotopes, primarily within the solar system. Urey, along with his student Stanley Miller
, may be best remembered for the renowned Miller-Urey experiment
, which shows that a mixture of ammonia
, when exposed to ultraviolet radiation
, can interact to form amino acids
, the "building blocks" of terrestrial life. This experiment followed on from Urey's work on the oxygen
, and is considered to be pioneering work in the field of paleoclimatology
, as it attempts to explain the composition of the early Earth's atmosphere.
Techniques used by chemists
Equipment used by chemists
Chemistry in society
Chemistry in industry
Background color shows subcategory in the metal–metalloid–nonmetal trend: