CHEMISTRY GLOSSARY

aerosol    →   aerosol

Aerosols are colloidal dispersions of liquid or solid particles in a gas, as in a mist or smoke. The commonly used aerosol sprays contain an inert propellant liquefied under pressure. The pressure of the gas causes the mixture to be released as a fine spray (aerosol) or foam (aerogel) when a valve is opened.

aliquot    →   alikvot

Aliquot is a known volume of liquid that represents a part of some larger volume. It is usually taken with a pipette from a measured flask.

allomerism    →   alomerija

Allomerism is the appearance of substances with different chemical composition but the same crystalline form.

allomorphism    →   alomorfija

Allomorphism is the existence of chemical substances with same chemical composition in two or more crystalline forms. See Polymorphism.

alkanes    →   alkani

Alkanes (paraffins) are acyclic branched or unbranched hydrocarbons having the general formula C_nH_2n+2, and therefore consisting entirely of hydrogen atoms and saturated carbon atoms. In the systematic chemical nomenclature alkane names end in the suffix -ane. They form a homologous series (the alkane series) methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), etc. The lower members of the series are gases; the high-molecular mass alkanes are waxy solid. Generaly the alkanes are fairly unreactive. They form haloalkanes with halogens when irradiated with ultraviolet radiation. Alkanes are present in natural gas and petroleum.

allotrope    →   alotrop

Allotropes are the elements which exist in two or more different forms in the same physical state. Allotropes generally differ in physical properties and may also differ in chemical activity.

Diamond, graphite and fullerenes are three allotropes of the element carbon. Graphite is a soft, black, slippery substance; by contrast, diamond is one of the hardest substances known. The different properties of the allotropes arise from their chemical structures. Diamonds typically crystallize in the cubic crystal system and consist of tetrahedrally bonded carbon atoms. Graphite crystallizes in the hexagonal system. In the fullerenes, the carbon atoms taking the form of a hollow sphere, ellipsoid, or tube.

In some cases, the allotropes are stable over a temperature range, with a definite transition point at which one changes into the other. For instance, tin has two allotropes: white (metallic) tin stable above 13.2 °C and grey (nonmetallic) tin stable below 13.2 °C.

The term allotropes may also be used to refer to the molecular forms of an element. Ozone is a chemically active triatomic allotrope of the element oxygen.

alum    →   alaun

Alums are a group of isomorphic glacial double sulphates with the general formula

where M^I can be univalent cation K, Na, Rb, Cs, NH₄ or Tl, and M^III is trivalent Al, Cr, or Fe.

amalgam    →   amalgam

Amalgams are metals alloyed with mercury. They can be solid or liquid, depending upon the mass ratio of thawed metal. Amalgam examples are gold/mercury, silver/mercury and copper/mercury all of which are used in dentistry.

anhydrous    →   anhidrid

Anhydrous (without water) is an applied to minerals which do not contain water of crystallization or water of chemical combination. For example, strongly heated copper (II) sulphate pent hydrate (CuSO₄•5H₂O) produces anhydrous copper (II) sulphate (CuSO₄). Less stable and more dangerous to use than hydrated.

antifreeze    →   antifriz

Antifreeze is a substance added to the liquid (usually water) in the cooling systems of internal-combustion engines to lower its freezing point so that it does not solidify at sub-zero temperatures. The commonest antifreeze is ethane- 1.2-diol (ethylene glycol).