Krypton - Chemistry Encyclopedia
Krypton (from the Greek word kryptos, meaning "hidden"), is the second heaviest of the noble gases. It was discovered in 1898 by Sir William Ramsay and Morris Travers during their experiments with liquid air, air that has been liquefied by cooling.
Lanthanides - Chemistry Encyclopedia
The lanthanide or rare earth elements (atomic numbers 57 through 71) typically add electrons to the 4f orbitals as the atomic number increases, but lanthanum (4f0) is usually considered a lanthanide. Scandium and yttrium are also chemically similar to lanthanides.
Lanthanum - Chemistry Encyclopedia
Elemental lanthanum has a ground state (electronic configuration) of [Xe]5d6s2. Naturally occurring lanthanum is a mixture of two stable isotopes, 138La and 139La.
Lawrencium - Chemistry Encyclopedia
Lawrencium is a synthetic radioactive element and the last member of the actinide series. It was discovered in 1961 by Albert Ghiorso and his coworkers, who bombarded a target of isotopes of californium (249Cf–252Cf) with boron projectiles (either 10B or 11B) using the Heavy Ion Linear Accelerator (HILAC) at the University of California, Berkeley, producing isotopes of unknown element 103 of masses 257 and 258.
Lead - Chemistry Encyclopedia
Lead makes up only about 0.0013 percent of Earth's crust but was well known in the ancient world and was even mentioned in the Book of Exodus. The word "lead" is derived from the Anglo-Saxon word laedan.
Lewis Structures - Chemistry Encyclopedia
In 1902, while trying to find a way to explain the Periodic Table to his students, the chemist Gilbert Newton Lewis discovered that the chemistry of the main-group elements could be explained using a model in which electrons arranged around atoms are conceived as occupying the faces of concentric cubes. This model was based on four assumptions.
Lipid Bilayers - Chemistry Encyclopedia
Lipid bilayers form the fundamental structures of cell membranes and thus provide a semipermeable interface between the interior and exterior of a cell and between compartments within the cell. Bilayer-forming lipids are amphipathic molecules (containing both hydrophilic and hydrophobic components).
Lipids - Chemistry Encyclopedia
Lipids are a class of biomolecules that is defined by their solubility in organic solvents, such as chloroform, and their relative insolubility in water. Interactions among lipids and of lipids with other biomolecules arise largely from their hydrophobic ("water-hating") nature.
Liquid Crystals - Chemistry Encyclopedia
In 1888 the Austrian botanist and chemist Friedrich Reinitzer, interested in the chemical function of cholesterol in plants, noticed that the cholesterol derivative cholesteryl benzoate had two distinct melting points. At 145.5°C (293.9°F) the solid compound melted to form a turbid fluid, and this fluid stayed turbid until 178.5°C (353.3°F), at which temperature the turbidity disappeared and the liquid became clear.
Liquids - Chemistry Encyclopedia
A liquid is one state in which matter can exist. A liquid can take the shape of any container it is placed in (unlike a solid), but the volume of the liquid will always remain constant (unlike a gas).
Lithium - Chemistry Encyclopedia
Lithium is a soft, silvery alkali metal and has the lowest density of any metal. The word "lithium" is derived from "lithos" (Greek for "stone").
Low Density Lipoprotein (LDL) - Chemistry Encyclopedia
Lipids are nonpolar molecules and are relatively insoluble in aqueous solutions. At low concentrations, cholesterol and cholesterol esters, as well as other lipids, may form microscopic droplets called chylomicrons (lipid-protein complexes) that are somewhat stable in solution.
Lucretius - Chemistry Encyclopedia
Little is known about Titus Lucretius Carus beyond what can be gathered from his poem De rerum natura. He was born in about 95 B.C.E., but the exact date is uncertain.
Lutetium - Chemistry Encyclopedia
The mixture of oxides known as ytterbia was obtained from yttria by Jean-Charles-Galissard de Marignac in 1878. From ytterbia the oxides of three elements were isolated: ytterbium (named after the town of Ytterby) by Marignac; scandium (named after Scandinavia) by L.
Magnesium - Chemistry Encyclopedia
Magnesium was first recognized as an element by Joseph Black in 1755. In 1808 Sir Humphry Davy isolated the element, and in 1831 H.
Magnetism - Chemistry Encyclopedia
The magnetic properties of materials were recognized by the ancient Greeks, Romans, and Chinese, who were familiar with lodestone, an iron oxide mineral that attracts iron objects. Although the attractive or repulsive forces that act between magnetic materials are manifestations of magnetism familiar to everybody, the origin of magnetism lies in the atomic structure of matter.
Manganese - Chemistry Encyclopedia
Manganese is a hard, brittle, gray-white metal in group 7B of the Periodic Table. It was recognized as an element in 1774 by Swedish chemist Carl Wilhelm Scheele and isolated by his assistant Johan Gottlieb Gahn later that year.
Antoine Lavoisier - Chemistry Encyclopedia
Antoine-Laurent Lavoisier, born in Paris, France, is considered the father of modern chemistry. During the course of his career, Lavoisier managed to transform just about every aspect of chemistry.
Ernest Lawrence - Chemistry Encyclopedia
Ernest Orlando Lawrence was a pioneer of "big science," the use of complicated and expensive instrumentation by large teams of researchers.
Joseph-Achille Le Bel - Chemistry Encyclopedia
Joseph-Achille Le Bel, born in Pechelbronn, France, was, with Dutch physical chemist Jacobus Hendricus van't Hoff, the cofounder of modern stereochemistry. They independently established the relation between optical activity and asymmetric carbon compounds.
Nicolas Leblanc - Chemistry Encyclopedia
Nicolas Leblanc invented a method of making alkali soda from salt that became one of the most important chemical processes of the nineteenth century. Leblanc was born in Issoudun, France; his father managed an iron-works.
Henri Le Châtelier - Chemistry Encyclopedia
Henri-Louis Le Châtelier was born into a family of architects, engineers, and scientists in Paris. His family home was like a drop-in center for France's leading chemists.
Georges Leclanché - Chemistry Encyclopedia
In 1866 Georges-Lionel Leclanché was granted French patent no. 71,865, which described a remarkable advancement in the technology of the primary electrochemical cell.
Luis Leloir - Chemistry Encyclopedia
Luis Leloir was born in Paris in 1906. His parents were Argentine, and he resided in Buenos Aires from the age of two and for most of his career until his death in 1987.
Gilbert N Lewis - Chemistry Encyclopedia
Gilbert Newton Lewis was born on October 25, 1875, in West Newton, Massachusetts. A precocious child, he received his early education at home and learned to read by the age of three.
Justus von Liebig - Chemistry Encyclopedia
Justus von Liebig, one of the founders of modern chemistry, was born on May 12, 1803, in Darmstadt, Hesse, Germany. His father was a manufacturer of drugs and paints.
Joseph Lister - Chemistry Encyclopedia
Joseph Lister is known as the founder of antiseptic surgery, a significant advance in medicine developed in the nineteenth century. Infection of wounds and surgical incisions was a major cause of hospital deaths before Lister developed a way of preventing these infections with chemical antiseptics.
Kathleen Lonsdale - Chemistry Encyclopedia
Kathleen Lonsdale was born Kathleen Yardley in Newbridge, Ireland, on January 28, 1903. She was the youngest of ten children (four of whom died in infancy).