CHEMISTRY GLOSSARY

histidine    →   histidin

Histidine is an electrically charged amino acids with basic side chains. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested. Histidine is perhaps the most common and versatile catalytic residue in proteins. The imidazole sidechain of histidine has a pKa of approximately 6.0. This means that, at physiologically relevant pH values, relatively small shifts in pH will change its average charge. The unprotonated imidazole is nucleophilic and can serve as a general base, while the protonated form can serve as a general acid. In addition, it is often a ligand for transition metal ions such as iron and zinc.

• Abbreviations: His, H
• IUPAC name: 2-amino-3-(1H-imidazol-5-yl)propanoic acid
• Molecular formula: C₆H₉N₃O₂
• Molecular weight: 155.15 g/mol

holmium    →   holmij

Holmium was discovered by Per Theodore Cleve (Sweden) in 1879. The origin of the name comes from the Greek word Holmia meaning Stockholm. It is fairly soft, malleable, lustrous, silvery metal. Reacts slowly with oxygen and water. Dissolves in acids. Can react violently with air or halogens. Holmium occurs in gadolinite. Most often from monazite sand. It has very few practical applications; however, it has some unusual magnetic properties that offer some hope for future applications.

hydrogen    →   vodik

Hydrogen was discovered by Sir Henry Cavendish (England) in 1766. The origin of the name comes from the Greek words hydro and genes meaning water and generate. It is colourless, odourless gas, burns and forms explosive mixtures in air. Reacts violently with oxidants. Hydrogen is the most abundant element in the universe. Commercial quantities of hydrogen are produced by reacting superheated steam with methane or carbon. In lab work from reaction of metals with acid solutions or electrolysis. Most hydrogen is used in the production of ammonia and in metal refining. Also used as fuel in rockets. Its two heavier isotopes (deuterium and tritium) used respectively for nuclear fusion.

indium    →   indij

Indium was discovered by Ferdinand Reich and Hieronymus Theodor Richter (Germany) in 1863. Named after the indicum (colour indigo), the colour it shows in a spectroscope. It is rare, very soft, silver-white metal. Stable in air and water. Dissolves in acids. Metal can ignite and burn. Indium is found in certain zinc ores. Used to coat high speed bearings and as an alloy that lowers the melting point of other metals. Relatively small amounts are used in dental items and in electronic semiconductors.

inert electrode    →   inertna elektroda

Inert electrode is an electrode that serves only as a source or sink for electrons without playing a chemical role in the electrode reaction. Precious metals, mercury, and carbon are typically used as inert electrodes. The inert nature of the electrode can sometimes be questioned. While the electrode may not take part in the reaction as a reactant or product, it still can act as an electrocatalyst.

iodine    →   jod

Iodine was discovered by Bernard Courtois (France) in 1811. The origin of the name comes from the Greek word iodes meaning violet. It is shiny, black, non-metallic solid with characteristic odour. Sublimes easily and as a gas it is violet and intensely irritating to the eyes, nose and throat. Iodine occurs on land and in the sea in sodium and potassium compounds. Required in small amounts by humans. Once used as an antiseptic, but no longer due to its poisonous nature.

iridium    →   iridij

Iridium was discovered by Smithson Tennant (England) in 1803. The origin of the name comes from the Latin word iris, meaning rainbow, because its salts are highly colored. It is heavy, brittle, white metal. Unreactive in air, water and acids. Attacked by fused NaOH. Metal ignites and burns readily. Iridium is found in gravel deposits with platinum. Used with osmium to tip gold pen points, to make crucible and special containers. Also to make alloys used for standard weights and measures and heat-resistant alloys. Also as hardening agent for platinum.

iron    →   željezo

Iron has been known since ancient times. The origin of the name comes from the Latin word ferrum meaning iron. It is malleable, ductile, silvery-white metal. Exposed surfaces form red-brown oxides. Forms very strong alloys (steel). Ferromagnetic. Metal dust flammable. Fourth most abundant element in the earth’s crust. Iron is obtained from iron ores. Pure metal produced in blast furnaces by layering limestone, coke and iron ore and forcing hot gasses into the bottom. This heats the coke red hot and the iron is reduced from its oxides and liquefied where it flows to the bottom. Iron is the most common metal in human society. More than 90 % of all metal refined in the world is iron. Used in steel and other alloys. It is the chief constituent of hemoglobin which carries oxygen in blood vessels. Its oxides are used in magnetic tapes and disks.

lanthanides    →   lantanoidi

Lanthanides (lanthanons, lanthanoids or rare-earth elements) are a series of fourteen elements in the periodic table, generally considered to range in proton number from cerium to lutetium inclusive. It was convenient to divide these elements into the cerium group or light earth: cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu); and the yttrium group or heavy earths: gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) i lutetium (Lu). The position of lanthanum is somewhat equivocal and, although not itself a lanthanide, it is often included with them for comparative purpose. The lanthanides are sometimes simply called the rare earths. Apart from unstable Pm, the lanthanides are actually not rare. Cerium is the 26. most abundant of all elements, 5 times as abundant as Pb. All are silvery very reactive metals.

lanthanum    →   lantan

Lanthanum was discovered by Carl Gustaf Mosander (Sweden) in 1839. The origin of the name comes from the Greek word lanthanein meaning to lie hidden. It is soft, silvery-white, malleable, ductile metal. Readily tarnishes in air. Reaction with water releases hydrogen gas. Metal ignites and burns readily. Reacts with oxidants. Lanthanum is found with rare earths in monazite and bastnasite. Monazite sand typical contains 25 % lanthanum. It is used in the electrodes of high-intensity, carbon-arc lights. Because it gives glass refractive properties, it is used in expensive camera lenses.