CHEMISTRY GLOSSARY

Neel temperature    →   Neelova temperatura

Néel temperature (T_N) is the critical temperature above which an antiferromagnetic substance becomes paramagnetic. The phenomenon was discovered around 1930 by the French physicist L.E.F. Néel (1904-2000).

neutrino    →   neutrino

Neutrino is a stable elementary particle in the lepton family. Neutrinos have zero (or at least near-zero) rest mass and spin 1/2.

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.

Gratzel solar cell    →   Gratzelova sunčeva ćelija

Grätzel solar cell is photoelectrochemical cell, developed by Michael Grätzel and collaborators, simulates some characteristics of the natural solar cell, which enables photosynthesis take place. In natural solar cell the chlorophyll molecules absorb light (most strongly in the red and blue parts of the spectrum, leaving the green light to be reflected). The absorbed energy is sufficient to knock an electron from the excited chlorophyll. In the further transport of electron, other molecules are involved, which take the electron away from chlorophyll. In Grätzel cell, the tasks of charge-carrier generation and transport are also assigned to different species.

His device consists of an array of nanometre-sized crystallites of the semiconductor titanium dioxide, welded together and coated with light-sensitive molecules that can transfer electrons to the semiconductor particles when they absorb photons. So, light-sensitive molecules play a role equivalent to chlorophyll in photosynthesis. In Grätzel cell, the light-sensitive molecule is a ruthenium ion bound to organic bipyridine molecules, which absorb light strongly in the visible range; titanium dioxide nanocrystals carry the received photoexcited electrons away from electron donors. On the other hand, a donor molecule must get back an electron, so that it can absorb another photon. So, this assembly is immersed in a liquid electrolyte containing molecular species (dissolved iodine molecules) that can pick up an electron from an electrode immersed in the solution and ferry it to the donor molecule. These cells can convert sunlight with efficiency of 10 % in direct sunlight and they are even more efficient in diffuse daylight.

half-cell    →   polučlanak

Half-cell is a part of galvanic cell in which oxidations or reduction of an element in contact with water or water solution one of its compounds.

nominal    →   nominalno

Nominal is used to describe a process where 100 % accuracy is not guaranteed. For example, sand filtres are usually sold to filtre to a nominal 10 μm, which means that they will filtre most particles of 10 μm and larger, but not all. A filtre which is guaranteed to filtre all particles of 10 μm would be termed absolute rather than nominal.

nucleophile    →   nukleofil

Nucleophiles are negatively charged or bear a partial negative charge. Examples are lone pairs or a hydroxide ion.

oxidation    →   oksidacija

The term oxidation originally meant a reaction in which oxygen combines chemically with another substance. More generally, oxidation is a part of a chemical reaction in which a reactant loses electrons (increases oxidation number). Simultaneous reduction of a different reactant must occur (redox reaction).

halogens    →   halogeni elementi

Halogens are the elements fluorine (F) chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are non-metals, and make up part of the 17 group in the periodic table. Compounds of these elements are called halogenides or halides.

The halogens all have a strong unpleasant odour and will burn flesh. They do not dissolve well in water. The five elements are strongly electronegative. They are oxidising agents, with fluorine being the strongest and astatine being the weakest. They react with most metals and many non-metals.

Halogens form molecules which consist of atoms covalently bonded. With increasing atomic weight there is a gradation in physical properties. For example: Fluorine is a pale green gas of low density. Chlorine is a greenish-yellow gas 1.892 times as dense as fluorine. Bromine is a deep reddish-brown liquid which is three times as dense as water. Iodine is a grayish-black crystalline solid with a metallic appearance. And astatine is a solid with properties which indicate that it is somewhat metallic in character.

heavy water    →   teška voda

Water molecules are composed of two hydrogen atoms and one oxygen atom (H₂O). If the hydrogen atoms of a water molecule are replaced by deuterium atoms, the result is heavy water (D₂O). Deuterium differs from hydrogen by having one neutron in the nucleus of the atom. There is approx. one part in 5000 D₂O in normal water and it can be concentrated by electrolysis. Heavy water has a higher boiling point (101.4 °C) and melts at 3.6 °C. Heavy water is 20/18=1.11 times heavier than ordinary water.