CHEMISTRY GLOSSARY

density    →   gustoća

In the most common usage, density (ρ) is mass density or mass per unit volume. In Si units it is measured in kg m^-3. More commonly, densities are given in kg dm^-3.

More generally, it is the amount of some quantity (mass, charge, energy, etc.) divided by a length, area, or volume.

Relative density is the ratio of the density of a substance to the density of some reference substance. For liquids or solids, it is the ratio of the density (usually at 20 °C) to the density of water at 4 °C. This quantity was formerly called specific gravity.

deoxyribonucleic acid    →   dezoksiribonukleinska kiselina

Deoxyribonucleic acid (DNA) is a nucleic acid with 2-deoxy-D-ribose as the sugar in its nucleotides. DNA contains encoded genetic information, specifically templates for the synthesis of all of an organism’s proteins and enzymes.

DNA was first identified in the 1869 by Swiss chemist Friedrich Miescher (1844-1895). In 1953, American biologist James Dewey Watson (1928-) and English physicist Francis Harry Compton Crick (1916–2004) had discovered that DNA occurs in the cell as a double helix, with two long strands of the molecule wound around each other, and further that the chemical structure of the molecule dictates that adenine (A) always aligns or pairs with thymine (T), and cytosine (C) always pairs with guanine (G). It is this base pairing that allows DNA in a cell to copy itself, and transfer its information to a new cell. The diameter of the helix is 2.0 nm and there is a residue on each chain every 0.34 nm in the z direction. The angle between each residue on the same strand is 36°, so that the structure repeats after 10 residues (3.4 nm) on each strand.

isothermal process    →   izotermni proces

Isothermal process is a thermodynamic process in which the temperature of the system does not change.

lanthanides contraction    →   kontrakcija lantanoida

Lanthanides contraction is a reduction of metal and ion diameters from lanthanum to lutetium and it is caused by a core charge growth inside the same shell. Elements which in the periodic system of elements come after lanthanides have, because of lanthanides contraction, smaller diameter than they should have according to their position in the periodic system of elements.

diamagnetism    →   dijamagnetizam

In diamagnetism the magnetisation is in the opposite direction to that of the applied field, i.e. susceptibility is negative. It results from changes induced in the orbits of electrons in the atoms of a substance by the applied field, the direction of the change opposing the applied flux.

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.

differential thermal analysis    →   diferencijalna termalna analiza

Differential thermal analysis (DTA) is a technique that is often used to analyze materials that react or decompose at higher temperatures. The difference in temperature between the sample and an inert reference material is monitored as both are heated in a furnace. Phase transitions and chemical reactions taking place in the sample on heating cause the temperature difference to become larger, at temperatures that are characteristic of the sample.

dipole    →   dipol

Dipole is a pair of separated opposite electric charges. Electric dipole is an assemblage of atoms or subatomic particles having equal electric charges of opposite sign separated by a finite distance. In the case of HCl, the electrons are attracted towards the more electronegative chlorine atom.

dipole molecule    →   dipolna molekula

Dipole molecules are created when mutual electronic pair at covalent bond is asymmetrical. If different atoms are bonded by a covalent bond, which can have different electron affinity, then the the atom with greater electron affinity will attract the electron pairs more strongly. In this way an asymmetrical distribution of negative charge appears in a molecule, so one part of the molecule becomes relatively negatively (the one closer to the electron pair) and the other becomes relatively positively charged.

line spectrum    →   linijski spektar

Red-hot gases give line spectrum, i.e. is they emit electromagnetic rays of defined wavelengths. That kind of emission line of spectrum is characteristic of each chemical element.