CHEMISTRY GLOSSARY

mass number    →   maseni broj

Mass number (A) is a characteristic property of a specific isotope of an element, equal to the sum of the number of protons and neutrons in the nucleus.

mass-energy equivalence    →   ekvivalencija mase i energije

In the special theory of relativity Einstein demonstrated that neither mass nor energy were conserved separately, but that they could be traded one for the other and only the total "mass-energy" was conserved. The relationship between the mass and the energy is contained in what is probably the most famous equation in science,

Where m is the mass of the object and c is the velocity of light. Cockcroft and Walton (1932) are routinely credited with the first experimental verification of mass-energy equivalence.

neutron    →   neutron

Neutron is an elementary particle on spin 1/2 and zero charge. The free neutron has an average lifetime of 887 seconds. Neutrons and protons, which are collectively called nucleons, are the constituents of the nucleus.

nucleon    →   nukleon

Nucleon is a collective term for the proton and neutron.

nuclide    →   nuklid

Nuclide is a species of atoms in which each atom has identical atomic number Z and identical mass number A. For example, a carbon-14 (C-14 or ¹⁴C) nuclide is the nucleus of a carbon atom, which has six protons and eight neutrons.

overpotential    →   prenapon

Overpotential (η) is a potential that must be applied in an electrolytic cell in addition to the theoretical potential required to liberate a given substance at an electrode. The value depends on the electrode material and on the current density.

molar mass    →   molarna masa

Molar mass is the mass of one mole of a substance.

It is normally expressed in units of g mol^-1, in which case its numerical value is identical with the relative molecular mass.

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.

nuclear magnetic resonance    →   nuklearna magnetska rezonancija

Nuclear magnetic resonance (NMR) is a type of radio-frequency spectroscopy based on the magnetic field generated by the spinning of electrically charged atomic nuclei. This nuclear magnetic field is caused to interact with a very large (1 T - 5 T) magnetic field of the instrument magnet. NMR techniques have been applied to studies of electron densities and chemical bonding and have become a fundamental research tool for structure determinations in organic chemistry.

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.