CHEMISTRY GLOSSARY

electron    →   elektron

The electron is an elementary particle with a negative electric charge of (1.602 189 2±0.000 004 6)×10^-19 C and a mass of 1/1837 that of a proton, equivalent to (9.109 534±0.000 047)×10^-31 kg.

In 1897 the British physicist Joseph John (J.J.) Thomson (1856-1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of bodies much smaller than atoms that he calculated as having a very large value for the charge to mass ratio. Later he estimated the value of the charge itself.

Electrons are arranged in from one to seven shells around the nucleus; the maximum number of electrons in each shell is strictly limited by the laws of physics (2n²). The outer shells are not always filled: sodium has two electrons in the first shell (2×1² = 2), eight in the second (2×2² = 8), and only one in the third (2×3² = 18). A single electron in the outer shell may be attracted into an incomplete shell of another element, leaving the original atom with a net positive charge. Valence electrons are those that can be captured by or shared with another atom.

Electrons can be removed from the atoms by heat, light, electric energy, or bombardment with high-energy particles. Decaying radioactive nuclei spontaneously emit free electrons, called β particles.

erbium    →   erbij

Erbium was discovered by Carl Gustaf Mosander (Sweden) in 1843. Named after Ytterby, a village in Sweden. It is soft, malleable, silvery metal. Reacts slowly with water. Dissolves in acids. Metal ignites and burns readily. Erbium is found with other heavier rare earths in xenotime and euxenite. Erbium oxide is used in ceramics to obtain a pink glaze. Also a few uses in the nuclear industry and as an alloying agent for other exotic metals.

europium    →   europij

Europium was discovered by Eugene Demarcay (France) in 1896. Named for the continent of Europe. It is soft, silvery-white metal. Extremely reactive with oxygen and water. Europium is obtained from monazite sand, which is a mixture of phosphates of calcium, thorium, cerium and most other rare earths. Used with yttrium oxide to make red phosphors for colour televisions.

explosive    →   eksploziv

Explosive is a compound or mixture that, when ignited or detonated, undergoes rapid violent chemical reaction that produces large amount of gas and heat, accompanied by light, sound and a high pressure shock wave.

flammable limit    →   granica zapaljivosti

Flammable limits refer to the conditions under which a mixture of a flammable material and air may catch fire or explode. When vapour s of a flammable or combustible liquid are mixed with air in the proper proportions in the presence of a source of ignition, rapid combustion or an explosion can occur. The proper proportion is called the flammable range and is also often referred to as the explosive range. The flammable range includes all concentrations of flammable vapour or gas in air, in which a flash will occur or a flame will travel if the mixture is ignited.

The lower flammable limit (LEL) or the lower explosive limit is the lowest concentration of a flammable vapour or gas in air that will propagate a flame from an ignition source. The upper flammable limit (UEL) or the upper explosive limit is the highest concentration of a flammable vapour or gas in air that will propagate a flame from an ignition source. Any concentration between these limits can ignite or explode.

foam    →   pjena

Foams are dispersions of gases in liquids or solids. The gas globule may be of any size, from colloidal to macroscopic, as in soap bubbles. Bakers’ bread and sponge rubber are examples of solid foams. Typical liquid foams are those used in fire-fighting, shaving creams, etc. Foams made by mechanical incorporation of air are widely used in the food industry (e.g. whipped cream, egg white, ice cream, etc.). Foams can be stabilized by surfactants.

Frasch proces    →   Fraschov postupak

Frasch proces is a method of obtaining sulphur from underground deposits using a tube consisting of three concentric pipes. Superheated steam is passed down the outer pipe to melt the sulphur, which is forced up through the middle pipe by compressed air fed through the inner tube. The steam in the outer casing keeps the sulphur molten in the pipe. It was named after the German-born American chemist Herman Frasch (1851-1914).

fuel cell    →   gorivi članak

Fuel cell is a device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues as long as fuel and oxidising agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell where spontaneous chemical reactions occur at the electrodes. The fuel is oxidised at the anode, and the oxidising agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., petrol or natural gas) must be converted (reformed) into hydrogen before they can be utilised in a fuel cell.

Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte. These fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at temperatures of several hundred degrees centigrade (Celsius). Others employ ionically conductive solids as electrolyte and must operate close to 1 000 °C.

gadolinium    →   gadolinij

Gadolinium was discovered by Jean de Marignac (France) in 1880. Named after the mineral gadolinite, named for J. Gadolin, a Finnish chemist and mineralogist. It is soft, ductile, silvery-white metal. Reacts slowly with water and oxygen. Dissolves in acids. Metal ignites and burns readily. Gadolinium is found with other rare earths in gadolinite and monazite sand. Used in steel alloying agents and the manufacture of electronic components.

gallium    →   galij

Gallium was discovered by Lecoq de Boisbaudran (France) in 1875. The origin of the name comes from the Latin word Gallia meaning France. It is soft, blue-white metal. Stable in air and water. Reacts violently with chlorine and bromine. Gallium is found throughout the crust in minerals like bauxite, germanite and coal. Used in semiconductor production. It us used in making LED’s (light-emitting diodes) and GaAs laser diodes.