CHEMISTRY GLOSSARY

congener    →   srodnost

Congener is a term in chemistry that refers to one of many variants or configurations of a common chemical structure. Elements belonging to the same group on the periodic table. For example, sodium and potassium are congeners.

bismuth    →   bizmut

Bismuth was discovered by Claude Geoffroy (France) in 1753. The origin of the name comes from the German words Weisse Masse meaning white mass; now spelled wismut and bisemutum. It is hard, brittle, steel-grey metal with a pink tint. Stable in oxygen and water. Dissolves in concentrated nitric acid. Bismuth can be found free in nature and in minerals like bismuthine (Bi₂S₃) and in bismuth ochre (Bi₂O₃) Main use is in pharmaceuticals and low melting point alloys used as fuses.

Bohr magneton    →   Bohrov magneton

Bohr magneton (μ_B) is the atomic unit of magnetic moment, defined as

where h is Planck’s constant, m_e the electron mass, and e the elementary charge. It is the moment associated with a single electron spin.

Born-Haber cycle    →   Born-Haberov kružni proces

Born-Haber cycle is a cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction

The standard enthalpy of formation of the ionic solid is the enthalpy of the reaction

The cycle involves equating this enthalpy (which can be measured) to the sum of the enthalpies of a number of steps proceeding from the elements to the ionic solid. The steps are:

1) Atomization of the metal

2) Atomization of the nonmetal

3) Ionisation of the metal

This is obtained from the ionisation potential.

4) Ionisation of the nonmetal

This is electron affinity.

5) Formation of the ionic solids

Equation of the enthalpies gives

from which ΔH_L can be found.

depression of freezing point    →   snižavanje ledišta

Depression of freezing point of a pure solvent is observed when substances are dissolved in it. The amount by which the freezing point is depressed is proportional to the number of molecules of solute and independent of their nature.

detergent    →   deterdžent

Detergent is a substance added to water to improve its cleaning properties. Although water is a powerful solvent for many compounds, it will not dissolve grease and natural oils. Detergents are compounds that cause such nonpolar substances to go into solution in water. Soap is the original example, owing its action to the presence of ions formed from long-chain fatty acids ion (e.g. stearat ion, CH₃(CH₂)₁₆COO^-).

elastomer    →   elastomer

Elastomer is a natural or synthetic rubber or rubberoid material, which has the ability to undergo deformation under the influence of a force and regain its original shape once the force has been removed.

boron    →   bor

Boron compounds have been known for thousands of years, but the element was not discovered until 1808 by Sir Humphry Davy (England) and independently by Joseph-Louis Gay-Lussac (France) and L. J. Thenard (France). The origin of the name comes from the Arabic word buraq and the Persian word burah meaning boraks. It is hard, brittle, lustrous black semimetal. Unreactive with oxygen, water, alkalis or acids. Combines with most metals to form borides. Boron is obtained from kernite, a kind of borax (Na₂B₄O₇·10H₂O). High purity boron is produced by electrolysis of molten potassium fluroborate and potassium chloride (KCl). Amorphous boron is used in pyrotechnic flares to provide a distinctive green color and in rockets as an igniter.

brass    →   mjed

Brasses are alloys of copper and zinc (generally 5 % to 40 %). Brass has been known to man since prehistoric times, long before zinc itself was discovered. It was produced by melting copper together with calamine, a zinc ore. Its ductility reaches a maximum with about 30 % zinc and its tensile strength with 45 % although this property varies greatly with the mechanical and heat treatment of the alloy. Typical applications included gears, plumbing ware fittings, adapters, valves and screw machine products. The French horn is a valved brass wind instrument.

Brass may contain small amounts of other alloying elements, such as aluminum, lead, tin, or nickel. Lead can be added as an alloying element resulting in a brass that can be rapidly machined and produces minimal tool wear. Additions of aluminium, iron and manganese to brass improve strength, whilst silicon additions improve wear resistance. Brass containing tin (< 2 % ) is less liable to corrosion in seawater; it is sometimes called naval brass and is used in naval construction.

Bunsen, Robert Wilhem    →   Bunsen, Robert Wilhem

Robert Wilhem Bunsen (1811-1899) is a German chemist who held professorships at Kassel, Marburg and Heidelberg. His early researches on organometallic compound of arsenic cost him an eye in an explosion. Bunsen's most important work was in developing several techniques used in separating, identifying, and measuring various chemical substances. He also improvement chemical battery for use in isolating quantities of pure metals - Bunsen battery.

The essential piece of laboratory equipment that has immortalized the name of Bunsen was not invented by him. Bunsen improved the burner's design, which had been invented by Faraday, to aid his endeavors in spectroscopy. Use of the Bunsen burner in conjunction with a glass prism led to the development of the spectroscope in collaboration with the German physicist Gustav Kirchoff and to the spectroscopic discovery of the elements rubidium (1860) and cesium (1861).