CHEMISTRY GLOSSARY

beta radiation    →   beta zračenje

Streams of beta particles are known as beta ray or beta radiation. Beta rays may cause skin burns and are harmful within the body. A thin sheet of metal can afford protection to the skin.

charge number    →   nabojni broj

Charge number represents ion charge of an atom or a group. It is denoted as a right superscript (Fe²⁺ or SO₄^2-).

conductivity    →   vodljivost

Conductivity is a measure of the ability of a material to conduct electric current.

alpha particle    →   alfa-čestica

Alpha particle is a helium nucleus emitted spontaneously from radioactive elements, both natural and manufactured. Its energy is in range 4-8 MeV and is dissipated in a very short path, i.e. a few centimetres of air or less than 0.005 mm of aluminium. As helium nucleus consists of two protons and two neutrons bound together as a stable entity the loss of an alpha particle involves a decrease in nucleon number of 4 and decrease of 2 in the atomic number, e.g.

A stream of alpha particles is known as an alpha ray or alpha-radiation.

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.

ampere    →   amper

Ampere (A) is the SI base unit of electric current.

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2×10^-7 newton per metre of length.

aspartic acid    →   asparaginska kiselina

Aspartic acid is an electrically charged amino acids with acidic side chains. As a group the charged amino acids are relatively abundant and are generally located on the surface of the protein. Aspartic acid and glutamic acid play important roles as general acids in enzyme active centers, as well as in maintaining the solubility and ionic character of proteins. Aspartic acid (sometimes referred to as asparate depending on pH) is non-essential in mammals, being produced from oxaloacetate by transamination.

• Abbreviations: Asp, D
• IUPAC name: 2-aminobutanedioic acid
• Molecular formula: C₄H₇NO₄
• Molecular weight: 133.10 g/mol

Donnan potential    →   Donnanov potencijal

Donnan potential is the electrical potential difference between two solutions separated by an ion-exchange membrane in the absence of any current flowing through the membrane

analytical balance    →   analitička vaga

Analytical balances are instruments used for precise determining mass of matter. Analytical balances are sensitive and expensive instruments, and upon their accuracy and precision the accuracy of analysis result depends. The most widely used type of analytical balances are balances with a capacity of 100 g and a sensitivity of 0.1 mg. Not one quantitative chemical analysis is possible without usage of balances, because, regardless of which analytical method is being used, there is always a need for weighing a sample for analysis and the necessary quantity of reagents for solution preparation.

The working part of the balance is enclosed in a glass-fitted case. The baseplate is usually of black glass or black slate. The beam has agate knife-edges at its extremes, supporting stirrups from which balance pans are suspended. Another agate or steel knife-edge is fixed exactly in the middle of the beam on its bottom side. This knife-edge faces downwards and supports the beam. When not in use and during loading or unloading of the pans, the balance should be arrested.

The principle of operation of a modern laboratory balance bears some resemblance to its predecessor - the equal arm balance. The older instrument opposed the torque exerted by an unknown mass on one side of a pivot to that of an adjustable known weight on the other side. When the pointer returned to the center position, the torques must be equal, and the weight was determined by the position of the moving weights.

Modern electronic laboratory balances work on the principle of magnetic force restoration. In this system, the force exerted by the object being weighed is lifted by an electromagnet. A detector measures the current required to oppose the downward motion of the weight in the magnetic field.

atom radius    →   radijus atoma

Atoms and molecules have no strict boundaries. The volume of a free atom is usually defined as that volume that contains 90 % of electron cloud. The radius of an atom represents half of interatom distance of two identical atoms which are in touch but are not interconnected either by a covalent or an ionic bond, but with a very weak van der Waals’s bond.