Acetaminophen - Chemistry Encyclopedia

The drug acetaminophen is a pain reliever (an analgesic) and a fever-reducing agent (an antipyretic). It is found in over-the-counter medicines such as Tylenol and Excedrin.

Acetylcholine - Chemistry Encyclopedia

Acetylcholine is the neurotransmitter produced by neurons referred to as cholinergic neurons. In the peripheral nervous system acetylcholine plays a role in skeletal muscle movement, as well as in the regulation of smooth muscle and cardiac muscle.

Acetylsalicylic Acid - Chemistry Encyclopedia

Aspirin (acetylsalicylic acid, see Figure 1) was introduced as an analgesic (pain-relieving agent) in the late nineteenth century by chemists at Bayer, a German pharmaceutical company. Acetylsalicylic acid is a prodrug and is transformed in the body to salicylate, the active form of the drug.

Acid-Base Chemistry - Chemistry Encyclopedia

Acids and bases have been known by their properties since the early days of experimental chemistry. The word "acid" comes from the Latin acidus, meaning "sour" or "tart," since water solutions of acids have a sour or tart taste.

Acne Medication - Chemistry Encyclopedia

Acne is a skin condition in which pimples (comedones) appear on the skin, usually on the face, chest, or back. Adolescents and young adults are most often afflicted.

Actinides - Chemistry Encyclopedia

The actinide elements (atomic numbers 89 through 103) involve the filling of 5f orbitals. All actinides are radioactive, but only uranium and the lighter actinides have half-lives long enough to be present in Earth's environment.

Actinium - Chemistry Encyclopedia

Actinium has thirty-six isotopes, all of which are radioactive and which range in mass number from 209 to 234. The longest-lived isotope has a mass number of 227 and a half-life of 21.8 years.

Active Site - Chemistry Encyclopedia

Enzymes play a vital role in the majority of biochemical reactions. Not only do they allow for life as we know it, they demonstrate remarkable specificity in many cases.

Adhesives - Chemistry Encyclopedia

An adhesive is a substance that sticks to the surface of an object such that two surfaces become bonded. A typical home improvement store carries many different adhesives for many different applications.

Agricultural Chemistry - Chemistry Encyclopedia

Agricultural chemistry must be considered within the context of the soil ecosystem in which living and nonliving components interact in complicated cycles that are critical to all living things. Carbon inputs from photosynthetic organisms ultimately provide the fuel for many soil organisms to grow and reproduce.

Air Pollution - Chemistry Encyclopedia

Air pollution is the presence in the atmosphere of any substance at a concentration great enough to produce an undesirable effect on humans, animals, vegetation, or materials, or to significantly alter the natural balance of any ecosystem. Air pollutants can be solids, liquids, or gases, and can have local, regional, and global impacts.

Alchemy - Chemistry Encyclopedia

The alchemical period corresponds to the span of human history that preceded the era in which fundamental understanding in the chemical sciences began to be acquired by humankind. Most scholars believe that alchemy had its roots in ancient Egypt.

Alkali Metals - Chemistry Encyclopedia

Alkali metals are the six elements that comprise Group I in the Periodic Table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Especially when dissolved in water, these elements form strong bases (alkalis) capable of reacting with and neutralizing strong acids.

Alkaline Earth Metals - Chemistry Encyclopedia

Alkaline earth metals are the six elements forming Group IIa in the Periodic Table: beryllium (Be), magnesium (Mg), Calcium (Ca), Barium (Ba), Strontium (Sr), and Radium (Ra)✶. Their oxides are basic (alkaline), especially when combined with water.

Allosteric Enzymes - Chemistry Encyclopedia

Enzymes are biological catalysts. They accelerate the rates of reactions in cells without being changed themselves during the process of reaction.

Allotropes - Chemistry Encyclopedia

Allotropes are different forms of the same element. Different bonding arrangements between atoms result in different structures with different chemical and physical properties.

Aluminum - Chemistry Encyclopedia

Aluminum is a silvery-white metallic element discovered in 1825 by Danish chemist Hans Christian Ørsted. It is the most abundant metal found in Earth's crust, comprising 8.3 percent of the crust's total weight.

Americium - Chemistry Encyclopedia

Americium is a synthetic radioelement, first produced in 1944 via the bombardment of plutonium with neutrons by Glenn Seaborg and coworkers as part of the Manhattan Project. The first isolation of a compound of americium, Am(OH)3, was achieved by B.

Amino Acid - Chemistry Encyclopedia

In 1953, Harold Urey and Stanley Miller carried out an amazing experiment in which they produced "molecules of life" from a mixture of gases that they proposed existed in a primordial earth. The experiments simulated what would happen when lightning strikes provided energy for chemical reactions in the atmosphere and suggested a hypothesis for how life might have developed on our planet.

Analytical Chemistry - Chemistry Encyclopedia

Analytical chemistry is the branch of chemistry that deals with determining the identity and concentration of chemical substances (analytes). G.

Antibiotics - Chemistry Encyclopedia

Antibiotics are substances that inhibit the growth of microorganisms (anti-metabolites) or their replication (a bacteriostatic effect). They were traditionally obtained by extracting them from cultures of microbes.

Antimony - Chemistry Encyclopedia

Antimony is a metalloid element, or a semimetal, its chemical behavior being between those of metals and nonmetals. It is a substance that was known in the ancient world.

Argon - Chemistry Encyclopedia

Argon is an odorless, colorless monatomic gas at room temperature. Although it constitutes about 1 percent of the atmosphere, it was not discovered until 1894, when John William Strutt (Lord Rayleigh) and William Ramsay isolated it from the more reactive components of air.

Aromaticity - Chemistry Encyclopedia

The literal meaning of "aromaticity" is "fragrance," but the word has a special meaning in chemistry. Aromaticity has to do with the unusual stability of the compound benzene and its derivatives, as well as certain other unsaturated ring compounds.

Abu-Bakr Muhammed ibn Zakariya Al-Razi - Chemistry Encyclopedia

Abu-Bakr Muhammed ibn Zakariya al-Razi (also transliterated as ar-Razi) was born around 854 in Ray, near the city of Teheran (the Persian Empire, now Iran). Al-Razi (in the Latinized West, Rhazes) achieved mastery in a number of fields, including philosophy, logic, poetry, and music.

Christian Anfinsen - Chemistry Encyclopedia

Christian Boehmer Anfinsen was born in Monessen, Pennsylvania, on March 26, 1916. He earned a B.A.

Svante Arrhenius - Chemistry Encyclopedia

Svante August Arrhenius, born in Vik, Sweden, is regarded as the cofounder of modern physical chemistry. For his theory of electrolytic dissociation, Arrhenius received the Nobel Prize in chemistry in 1903.