CHEMISTRY GLOSSARY

effective nuclear charge    →   efektivni naboj jezgre

Effective nuclear charge. (Z_eff) is the nuclear charge experienced by an electron when other electrons are shielding the nucleus.

insulator    →   izolator

Insulator is a material in which the highest occupied energy band (valence band) is completely filled with electrons, while the next higher band (conduction band) is empty. Solids with an energy gap of 5 eV or more are generally considered as insulators at room temperature. Their conductivity is less than 10^-6 S/m and increases with temperature.

metallic bond    →   metalna veza

Metallic bond is a electrostatic attraction binding the positive ions of a solid metal together by means of a "sea" of delocalised valence electrons

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).

VSEPR    →   VSEPR

Valence shell electron pair repulsion theory (VSEPR) is a model that explains the shapes of molecules by assuming that electron pairs arrange themselves around atoms in a way that minimizes electron-electron repulsions.

ionisation    →   ionizacija

Ionisation is the process of producing ions. Certain molecules ionise in a solution; for example, acids ionise when dissolved in water.

Electron transfer also causes ionisation in certain reactions, for example sodium and chlorine react by transfer of a valence electron from the sodium atom to the chlorine atom to form the ions that constitute a sodium chloride crystal.

Lewis structure    →   Lewisova struktura

Lewis structure is the representation of the electron arrangement in atoms, ions, or molecules by showing the valence electrons as dots placed around the symbols for the elements.

Lewis symbols    →   Lewisovi simboli

Lewis symbols are the shorthand electron dot structure of an atom.

molecular shape    →   oblik molekule

Molecular shape is the three dimensional arrangement of atoms in space around a central atom. The molecular formula of a substance does not give an indication of its shape. For example, CO₂ is a linear molecule, but SO₂ is angular.

The three-dimensional shapes of many small molecules can be predicted by applying the valence shell electron pair repulsion theory (VSEPR). When atoms combine to form molecules, pairs of valence electrons arrange themselves as far from each other as possible. Another way to characterize molecular shape is in terms of hybrid orbitals.

semiconductor    →   poluvodič

Semiconductor is a material in which the highest occupied energy band (valence band) is completely filled with electrons at T = 0 K, and the energy gap to the next highest band (conduction band) ranges from 0 to 4 or 5 eV. With increasing temperature electrons are excited into the conduction band, leading to an increase in the electrical conductivity.