CHEMISTRY GLOSSARY

allotropy    →   alotropija

Allotropy (Gr. allos, other, and tropos, manner) is the phenomenon of an element existing in two or more physical forms in the same physical state. The difference between the forms involves either crystaline structure (white, red and black phosphorus), the number of atoms in the molecule of a gas (diatomic oxygen and triatomic ozone), or the molecular structure of a liquid (liquid helium an helium II).

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. This form allotropy is called enantiotropy. Form of allotropy, in which there is no transition temperature at which the two are in equilibrium, is called monotropy.

Allotropy does not apply to the substance existing in different physical states as, for example, when ice melts and changes from solid ice to liquid water.

Allotropy is generally restricted to describing polymorphic behaviour in elements, while polymorphism may refer to any material having multiple crystal structures.

californium    →   kalifornij

Californium was discovered by Stanley G. Thompson, Kenneth Street Jr. and Albert Ghiorso (USA) in 1950. Named after the State and University of California, USA. It is synthetic radioactive metal. Powerful neutron emitter. Californium was made by bombarding curium with helium ions.

aluminium    →   aluminij

Aluminium was discovered by Friedrich Wöhler (Germany) in 1827. The origin of the name comes from the Latin word alumen meaning alum. It is soft, lightweight, silvery-white metal. Exposed surfaces quickly form protective oxide coating. Metal reacts violently with oxidants. Third most abundant element in the earth’s crust. Aluminium is the most abundant metal to be found in the earth’s crust, but is never found free in nature. Aluminium is obtained by electrolysis from bauxite. Used for many purposes from airplanes to beverage cans. Too soft in its pure form so less than 1 % of silicon or iron is added, which hardens and strengthens it.

atmosphere    →   atmosfera

1. Atmosphere is the column of air which is extending several hundred kilometers above the surface the Earth's surface. The density of this air decreases as you proceed up from the surface. The air in the atmosphere consists of 78 % nitrogen, 21 % oxygen, and 0.9 % argon. The remaining 0.1 % of the atmosphere consists of ozone, water vapor, carbon dioxide, methane, helium, and neon. The atmosphere is divided into different regions. The lowest two layers are the troposphere (the layer closest to the earth) and the stratosphere respectively. These two layers contain more than 99 % of the atmospheric molecules.

2. Standard atmosphere (atm) is an obsolete pressure and stress unit which should be discontinued. It is unit of pressure equal to the air pressure measured at mean sea level.

1 atm = 101 325 Pa

Technical atmosphere (at) is an obsolete MKpS pressure and sttress derived unit.

1 at = 98 066.5 Pa

1 atm = 1.033 227 453 at

barium    →   barij

Barium was discovered by Sir Humphry Davy (England) in 1808. The origin of the name comes from the Greek word barys meaning heavy. It is soft, slightly malleable, silvery-white metal. Attacked by air and water. Soluble compounds toxic by ingestion. Barium is found in barytine (BaSO₄) and witherite (BaCO₃), never found in pure form due to its reactivity. Must be stored under kerosene to remain pure. Barite, or barium sulfate (BaSO₄), when ground is used as a filter for rubber, plastics and resins. It is insoluble in water and so is used in X-rays of the digestive system. Barium nitrate, Ba(NO₃)₂, burns brilliant green and is used in fireworks.

catalase    →   katalaza

Catalase is an enzyme which catalyzes the breakdown of hydrogen peroxide in the body into oxygen and water.

chalcogens    →   halkogeni elementi

Chalcogens are the Group 16 elements: oxygen (O), sulphur (S), selenium Se), tellurium (Te), and polonium (Po). Compounds of these elements are called chalcogenides.

combustion    →   gorenje

Combustion is a phenomenon when a substance is combined with oxygen in the presence of a flame accompanied by the production of heat and light. Combustion requires a supply of both fuel and oxygen (air) and can take place in the open atmosphere such as an open fire, or in a closed system, such as a car engine.

curium    →   kurij

Curium was discovered by Glenn T. Seaborg, Ralph A. James and Albert Ghiorso (USA) in 1944. Named in honour of Pierre and Marie Curie. It is silvery, malleable, synthetic radioactive metal. So radioactive it glows in the dark. Curium was made by bombarding plutonium with helium ions.

bomb calorimeter    →   kalorimetrijska bomba

Bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of samples which can be burned in oxygen. Four essential parts are required in any bomb calorimeter:

1. a bomb or vessel in which the combustible charges can be burned,
2. a bucket or container for holding the bomb in a measured quantity of water, together with a stirring mechanism,
3. an insulating jacket to protect the bucket from transient thermal stresses during the combustion process, and
4. a thermometer or other sensor for measuring temperature changes within the bucket.