Arsenic - Chemistry Encyclopedia
Arsenic is the twentieth most abundant element in Earth's crust, averaging a concentration of approximately 2 ppm. Arsenopyrite (FeAsS) is its most common mineral.
Artificial Sweeteners - Chemistry Encyclopedia
There are presently four artificial, or synthetic, sweeteners that have been approved by the U.S. Food and Drug Administration (FDA): saccharin, aspartame, acesulfame-K, and sucralose.
Ascorbic Acid - Chemistry Encyclopedia
Ascorbic acid or vitamin C is an antiscorbutic agent. Scurvy is a disease that potentially ranks as the second most important nutritional deficiency, after protein-calorie malnutrition.
Astatine - Chemistry Encyclopedia
Astatine is a radioactive halogen (the heaviest of the halogen elements) and is a solid at room temperature. Dale R.
Astrochemistry - Chemistry Encyclopedia
In the night sky, the expanses of space between the stars of the Milky Way appear to be empty. In fact this space is occupied by a very thin gas that is mostly hydrogen and that has mere traces (less than 0.1% by number of atoms) of other elements such as oxygen, carbon, and nitrogen.
Atmospheric Chemistry - Chemistry Encyclopedia
With each breath, the lungs inhale air filled with nitrogen and oxygen, the most abundant natural gases in the atmosphere. Also inhaled, however, are small quantities of gases and particles that are pollutants.
Atomic Nucleus - Chemistry Encyclopedia
The atomic nucleus is a tiny massive entity at the center of an atom. Occupying a volume whose radius is 1/100,000 the size of the atom, the nucleus contains most (99.9%) of the mass of the atom.
Atomic Structure - Chemistry Encyclopedia
The atom is now known to consist of three primary particles: protons, neutrons, and electrons, which make up the atoms of all matter. A series of experimental facts established the validity of the model.
Atoms - Chemistry Encyclopedia
An atom is the smallest possible unit of an element. Since all forms of matter consist of a combination of one or more elements, atoms are the building blocks that constitute all the matter in the universe.
Barium - Chemistry Encyclopedia
The fifty-sixth element in the Periodic Table, barium has been known in various mineral forms since the 1600s. However, it was not until the 1770s that Carl W.
Base Pairing - Chemistry Encyclopedia
deoxyribose and phosphates groups occupying (or being oriented toward) the outer surfaces, interacting with water. The 20-angstrom (7.9 × 10−8-inch) diameter of the helix was consistent with the presence of two adjacent strands and supported the hypothesis that a purine base resided on one strand and a pyrimidine base on the equivalent (homologous) site of the complementary strand.
Bases - Chemistry Encyclopedia
Bases are considered the chemical opposite of acids because of their ability to neutralize acids. In 1887 the Swedish physicist and chemist Svante Arrhenius defined a base as the chemical substance that produces hydroxide ions (OH−) and cations.
Berkelium - Chemistry Encyclopedia
Berkelium, element 97, is a synthetic radioelement, first synthesized by Glenn Seaborg's group in 1949. A target of a few milligrams of an isotope of americium (241Am) was bombarded with α-particles within a cyclotron at the University of California at Berkeley.
Beryllium - Chemistry Encyclopedia
Beryllium was identified as a unique element and as a constituent of the mineral beryl and the gem emerald by the French chemist Louis Vauquelin in 1797. Metallic beryllium was isolated in 1828 by the scientists (working independently of one another) Antoine Bussy and Friedrich Wöhler.
Bioluminescence - Chemistry Encyclopedia
Bioluminescence is the emission of visible light by biological systems, which arises from enzyme-catalyzed chemical reactions. Bioluminescence can be distinguished from chemiluminescence in that it occurs in living organisms and requires an enzyme catalyst.
Bismuth - Chemistry Encyclopedia
Bismuth is a brittle, crystalline metal that is white with a pinkish tint. It is the heaviest and only nontoxic member of the heavy metals.
Bleaches - Chemistry Encyclopedia
When chlorine gas is bubbled through a cylinder of tomato juice, the chlorine/tomato juice mixture turns almost completely white within five minutes. This spectacular change is a result of the chemical action of chlorine, acting as an oxidizing bleaching agent, on the pigments in tomato juice.
Oswald Avery - Chemistry Encyclopedia
By the early 1940s, scientists knew that chromosomes existed and that they were composed of smaller units called genes. Chemical analysis had revealed that the eucaryotic chromosome consists of about 50 percent protein and 50 percent deoxyribonucleic acid (DNA).
Amedeo Avogadro - Chemistry Encyclopedia
In 1811, just three years after John Dalton published his atomic theory, a brilliant theoretician named Amedeo Avogadro proposed his molecular theory. Avogadro's molecular theory related gas densities to molecular weights, explained reacting proportions by volume in terms of molecular ratios and compositions, and suggested methods for determining both molecular weights and compositions.
Leo Baekeland - Chemistry Encyclopedia
Born in St. Martens-Latem, Belgium, Leo Hendrick Baekeland was the son of a cobbler (Karel Baekeland) and a housemaid (Rosalia Merchie).
Johann Jakob Balmer - Chemistry Encyclopedia
The name of Johann Jakob Balmer is immortalized in the Balmer series of spectral lines emitted from the hydrogen atom. Atoms that are excited to higher energies return to lower energies by emitting electromagnetic radiation at specific frequencies.
John Bardeen - Chemistry Encyclopedia
In 1972 John Bardeen did something that no other physicist, not even Albert Einstein, had ever done. He won his second Nobel Prize in physics.
Antoine-Henri Becquerel - Chemistry Encyclopedia
Antoine-Henri Becquerel was born the son of the physicist Alexandre-Edmond Becquerel, and the grandson of the physicist Antoine-César Becquerel, and it is not surprising that he followed in their footsteps. It is also not surprising that his research interests centered around solar radiation and phosphorescence, as these are phenomena that his father had investigated.
Paul Berg - Chemistry Encyclopedia
Paul Berg is considered to be one of the few pioneers in molecular biology, which is essentially the application of chemistry to biological systems. His work with recombinant DNA provided scientists with a very valuable laboratory technique.
Claude-Louis Berthollet - Chemistry Encyclopedia
Claude-Louis Berthollet was influential in four areas: theoretical chemistry, experimental chemistry, practical chemistry, and chemical writing. He was also a chemistry teacher and, with his contemporary Pierre-Simon de Laplace, a patron of young French scientists.
Jöns Jakob Berzelius - Chemistry Encyclopedia
Before the early 1800s the symbols used to denote chemical elements and compounds were obscure. Alchemists wanted to keep their work secret and so devised symbols for the chemicals they used that would not reveal anything about them.
Joseph Black - Chemistry Encyclopedia
Joseph Black was trained as a medical doctor. One of his early scientific undertakings was investigating means of treating "the stone" (kidney stones and gallstones).
Niels Bohr - Chemistry Encyclopedia
Niels Bohr was one of the founders of modern atomic and nuclear physics. He was born into a family of intellectual and academic distinction.