CHEMISTRY GLOSSARY

isotope    →   izotop

Isotopes are two or more nuclides with the same atomic number Z but different mass number A. The term is sometimes used synonymously with nuclide, but it is preferable to reserve the word nuclide for a species of specific Z and A.

Dalton’s atomic theory    →   Daltonova atomska teorija

Dalton’s atomic theory is a theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates:

1. Elements consist of indivisible small particles (atoms).

2. All atoms of the same element are identical; different elements have different types of atom.

3. Atoms can neither be created nor destroyed.

4. ’Compound elements’ (i.e. compounds) are formed when atoms of different elements join in simple ratios to form ’compound atoms’ (i.e. molecules).

Dalton also proposed symbols for atoms of different elements (later replaced by the present notation using letters).

diastereoisomer    →   dijastereoizomer

Diastereoisomers (diastereomers) are stereoisomers of a compound having two or more chiral centers that are not a mirror image of another stereoisomer of the same compound. For example, in the structure below, 1 and 2 are enantiomers and so are 3 and 4; 1 and 3 are diastereoisomers, as are 2 and 4. Unlike enantiomers, diastereoisomers need not have closely similar physical and chemical properties

molecule    →   molekula

Molecule is the smallest part of a chemical compound that can take part in a chemical reaction. The atoms of a molecule are held together by chemical bonds.

groups in periodic system of elements    →   skupine periodnog sustava

Periodic system of elements is divided into 18 groups of chemical elements. Elements belonging to the same group have a same number of valence electrons and similar chemical properties. Elements of main groups are in 1., 2., and in groups 13. to 18. Different groups of elements can be named according to the first element in the group (elements of boron group, elements of carbon group), or they have some special names (noble gases, halogenic elements, halyde elements, earthalkali and alkali metals).

haematite    →   hematit

Haematite is a mineral of iron(III) oxide Fe₂O₃. It is the most important ore of iron and usually occurs in two main forms: as a massive red kidney-shaped ore and as grey to black metallic crystals known as specular iron ore. Haematite is the major red colouring agent in rocks; the largest deposits are of sedimentary origin. In industry haematite is also used as a polishing agent (jeweller’s rouge) and in paints.

glycoside    →   glikozid

Glycoside is one of a group of organic compounds in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bond. The sugar group is known as the glycon and the non-sugar group as the aglycon. According to the IUPAC definition, all disaccharides and polysaccharides are glycosides where the aglycone is another sugar.

In the free hemiacetal form, sugars will spontaneously equilibrate between the α and β anomers. However, once the glycosidic bond is formed, the anomeric configuration of the ring is locked as either α or β. Therefore, the alpha and beta glycosides are chemically distinct. They will have different chemical, physical, and biological properties. Many glycosides occur abundantly in plants, especially as flower and fruit pigments.

The term glycoside was later extended to cover not only compounds in which the anomeric hydroxy group is replaced by a group -OR, but also those in which the replacing group is -SR (thioglycosides), -SeR (selenoglycosides), -NR1R2 (N-glycosides), or even -CR1R2R3 (C-glycosides). Thioglycoside and selenoglycoside are legitimate generic terms; however the use of N-glycoside, although widespread in biochemical literature, is improper and not recommended here (glycosylamine is a perfectly acceptable term). C-Glycoside is even less acceptable. All other glycosides are hydrolysable; the C-C bond of C-glycosides is usually not. The use and propagation of names based on C-glycoside terminology is therefore strongly discouraged.

octet rule    →   pravilo okteta

Octet rule states that the chemical properties of the elements repeat on a regular basis with increasing atomic mass, and that the chemical properties of each eight element are similar. Since the inert gases, with the exception of helium have eight electrons in their outer shells, this stable electronic configuration is called the octet rule. In chemical reactions atoms of elements tend to react in such a way as to achieve the electronic configuration of the inert gas nearest to them in the periodic table. There are a number of exceptions to the octet rule.

periodic table of the elements    →   periodni sustav elemenata

Periodic table is a table of elements, written in sequence in the order of atomic number or atomic weight and arranged in horizontal rows (periods) and vertical columns (groups) to illustrate the occurrence of similarities in the properties of the elements as a periodic function of the sequence. The original form was proposed by Dmitri Mendeleev (1834-1907) in 1869, using relative atomic masses.

absorbance    →   apsorbancija

Absorbance (A) is a logarithm of the ratio of incident radiant power (P_o) to transmitted radiant power (P) through a sample (excluding the effects on cell walls).

The absorption of light by a substance in a solution can be described mathematically by the Beer-Lambert law

where A is the absorbance at a given wavelength of light, ε is the molar absorbtivity or extinction coefficient (L mol^-1 cm^-1), unique to each molecule and varying with wavelength, b is the length of light path through the sample (cm), and c is the concentration of the compound in solution (mol L^-1).