CHEMISTRY GLOSSARY

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.

neutron number    →   neutronski broj

Neutron number (N) is a characteristic property of a specific isotope of an element, equal to the number of neutrons in the nucleus.

concentration    →   koncentracija

1. Group of four quantities characterizing the composition of a mixture with respect to the volume of the mixture (mass, amount, volume and number concentration).

2. Short form for amount (of substance) concentration (substance concentration in clinical chemistry).

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.

electronegativity    →   elektronegativnost

Electronegativity is a parameter originally introduced by L. Pauling which describes, on a relative basis, the power of an atom to attract electrons. For example, in hydrogen chloride, the chlorine atom is more electronegative than the hydrogen and the molecule is polar, with a negative charge on the chlorine atom.

There are various ways of assigning values for the electronegativity of an element. Pauling electronegativities are based on bond dissociation energies using a scale in which fluorine, the most electronegative element, has the value 4 and francium, the lowest electronegative element, has the value 0.7.

energy    →   energija

Energy (E, U) is the characteristic of a system that enables it to do work. Like work itself, it is measured in joules (J).

The internal energy of a body is the sum of the potential energy and the kinetic energy of its component atoms and molecules.

Potential energy is the energy stored in a body or system as a consequence of its position, shape, or state (this includes gravitation energy, electrical energy, nuclear energy, and chemical energy).

Kinetic energy is the energy of motion and is usually defined as the work that will be done by a body possessing the energy when it is brought to rest. For a body of mass m having a speed v, the kinetic energy is mv²/2. Kinetic energy is most clearly exhibited in gases, in which molecules have much greater freedom of motion than in liquids and solids.

In an isolated system energy can be transferred from one form to another but the total energy of the system remains constant.

paramagnetism    →   paramagnetizam

Paramagnetism is a type of magnetism characterised by a positive magnetic susceptibility, so that the material becomes weakly magnetised in the direction of an external field. The magnetisation disappears when the field in removed.

PCl5 reaction    →   reakcija s PCl5

Reaction with phosphorus pentachloride (PCl₅) is a characteristic of organic compounds containing a hydroxyl group and this reaction is used to identify these compounds in an organic analysis.

Fajans’ rules    →   Fajansova pravila

Fajans’ rules, formulated by American chemist of Polish origin. Kazimierz Fajans (1887-1975), indicating the extent to which an ionic bond has covalent character caused by polarisation of the ions. Covalent character is more likely if:

1. the charge of the ions is high;

2. the positive ion is small or the negative ion is large;

3. the positive ion has an outer electron configuration that is not a noble- gas configuration.