CHEMISTRY GLOSSARY

corticosteroid    →   kortikosteroid

Corticosteroids are general term for hormones produced by the adrenal gland. Includes cortisol and cortisone which regulate the use of nutrients in the body.

crystal    →   kristal

Crystal is a solid with a regular geometric shape, having a characteristic internal structure and enclosed by symmetrically arranged plane surfaces, intersecting at definite and characteristic angles. In crystals the particles (atoms, ions, or molecules) have a regular three-dimensional repeating arrangement in space. This is called the crystal structure. The crystal lattice is the arrangement of points in space at which the particles are positioned.

cross-linking    →   umrežavanje

Cross-linking is an attachment of two chains of polymer molecules by bridges, composed of either an element, a group, or a compound, that join certain carbon atoms of the chains by primary chemical bonds, as indicated in the schematic diagram

Cross-linking occurs in nature in substances made up of polypeptide chains that are joined by the disulfide bonds of the cysteine residue, as in keratins or insulin. Cross-linking can be artificially effected, either adding a chemical substance (cross-linking agent), or by subjecting the polymer to high-energy radiation. Examples are: vulcanisation of rubber with sulphur, cross-linking of polystyrene with divinylbenzene, or cross-linking of polyethylene by means of high-energy radiation.

Cross-linking has the effect of changing a plastic from thermoplastic to thermosetting. Thus, it also increases strength, heat and electrical resistance, and especially resistance to solvents and other chemicals.

deuterium lamp    →   deuterijeva svjetiljka

Deuterium or hydrogen lamp is used as a source of continuous radiation in UV part of the spectrum.

dielectric constant    →   dielektrična konstanta

Dielectric constant or permittivity (ε) is an index of the ability of a substance to attenuate the transmission of an electrostatic force from one charged body to another. The lower the value, the greater the attenuation. The standard measurement apparatus utilises a vacuum whose dielectric constant is 1. In reference to this, various materials interposed between the charged terminal have the following value at 20 °C:

The exceptionally high value for water accounts for its unique behaviour as a solvent and in electrolytic solutions. Dielectric constant values decrease as the temperature rises.

diffusion    →   difuzija

Diffusion is the spontaneous mixing of one substance with another when in contact or separated by a permeable membrane. Diffusion is a result of the random motions of their component atoms, molecules, ions, or other particles. Diffusion occurs most readily in gases, less so in liquids, and least in solids. The rate of diffusion is proportional to the concentration of the substance and increases with temperature. The theoretical principles are stated in Fick’s laws.

dysprosium    →   disprozij

Dysprosium was discovered by Paul Emile Lecoq de Boisbaudran (France) in 1886. The origin of the name comes from the Greek word dysprositos meaning hard to obtain. It is soft, lustrous, silvery metal. Reacts with oxygen. Reacts rapidly with water; dissolves in acids. Metal ignites and burns readily. Reductant. Dysprosium usually found with erbium, holmium and other rare earths in some minerals such as monazite sand. Dysprosium uses are limited to the experimental and esoteric. Some isotopes of dysprosium are effective absorbers of thermal neutrons and are being considered for use in the control rods in nuclear reactors.

electromagnetic spectrum    →   elektromagnetski spektar

See Electromagnetic radiation spectrum

electromagnetic wave    →   elektromagnetski val

All matter absorbs and emits radiation covering a broad band of frequencies and wavelengths. Thus electromagnetic radiation has the velocity of light (2.998×10⁸ ms^-1) and arises from the vibrating electric charges in atoms and bonds. The range of wavelengths, also known as the electromagnetic spectrum, is shown below:

explosion    →   eksplozija

Explosion is a rapid violent chemical reaction that produces large amounts of gas and heat, accompanied by light, sound and a high-pressure shock wave.