CHEMISTRY GLOSSARY

hydrogen bond    →   vodikova veza

Hydrogen is a bond formed by a hydrogen atom to an electronegative atom, and is denoted by dashed lines H-X---H-B. A hydrogen atom covalently bound to an oxygen (electronegative atom) has a significant positive charge and can form a weak bond to another electronegative atom.

ionic radius    →   ionski radijus

Ionic radius is the radius of anions and cations in crystalline ionic compounds, as determined by consistently partitioning the center-to-center distance of ions in those compounds. In general, negative ions have larger ionic radii than positive ions.

ionic strength    →   ionska jakost otopine

Ionic strength (μ or I) is a measure of the total concentration of ions in a solution, defined by

where z_i is the charge of ionic species i and c_i is its concentration.

isoelectric point    →   izoelektrična točka

Isoelectric point (pI or IEP) is the pH of a solution or dispersion at which the net charge on the molecules or colloidal particles is zero. In electrophoresis there is no motion of the particles in an electric field at the isoelectric point. The net charge (the algebraic sum of all the charged groups present) of any amino acid, peptide or protein, will depend upon the pH of the surrounding aqueous environment. For example, alanine can have a charge of +1, 0, or -1, depending on the pH of the solution in which it is dissolved.

lawrencium    →   lawrencij

Lawrencium was discovered by Albert Ghiorso, Torbjorn Sikkeland, Almon E. Larsh and Robert M. Latimer (USA) in 1961. Named in honour of Ernest O. Lawrence, inventor of the cyclotron. It is synthetic radioactive metal. Lawrencium was produced by bombarding a mixture of three isotopes of californium with boron-10 and boron-11 ions. Eight isotopes of lawrencium have been synthesized to date, with the longest-lived being lawrencium-256, which has a half-life of about 30 seconds.

mass spectrometry    →   masena spectrometrija

Mass spectrometry is an analytical technique in which ions are separated according to the mass/charge (m/e) ratio and detected by a suitable detector.

In a mass spectrometer a sample is ionised and the positive ions produced are accelerated into a high-vacuum region containing electric and magnetic fields. These fields deflect and focus the ions onto a detector. A mass spectrum is thus obtained, consisting of a series of peaks of variable intensity to which m/e values can be assigned. Different molecules can be identified by their characteristic pattern of lines.

nobelium    →   nobelij

Nobelium was discovered by Nobel Institute of Physics in Stockholm and later by Albert Ghiorso, Torbjorn Sikkeland, J. R. Walton and Glenn T. Seaborg (USA) in 1958. Named in honour of Alfred Nobel, Swedish chemist who discovered dynamite and founder of the Nobel Prizes. It is synthetic radioactive metal. Nobelium was made by bombarding curium with carbon-13.

nonpolar molecule    →   nepolarna molekula

Nonpolar molecule is a molecule which has no separation of charge, so no positive or negative poles are formed. For example, the Cl₂ molecule has no polar bonds (molecule with one type of atom), CH₄ is a non-polar molecule (due to its symmetry). Nonpolar molecules do not dissolve in water as they cannot form hydrogen bonds (thus are hydrophobic) but do dissolve in lipids or fats (lipophilic).

nuclear magnetic resonance    →   nuklearna magnetska rezonancija

Nuclear magnetic resonance (NMR) is a type of radio-frequency spectroscopy based on the magnetic field generated by the spinning of electrically charged atomic nuclei. This nuclear magnetic field is caused to interact with a very large (1 T - 5 T) magnetic field of the instrument magnet. NMR techniques have been applied to studies of electron densities and chemical bonding and have become a fundamental research tool for structure determinations in organic chemistry.

nuclear reactor    →   nuklearni reaktor

Nuclear reactor is an assembly of fissionable material (uranium-235 or plutonium-239) designed to produce a sustained and controllable chain reaction for the generation of electric power.

The essential components of a nuclear reactor are:

1. The core, metal rods containing enough fissionable material to maintain a chain reaction at the necessary power level (as much as 50 t of uranium may be required).
2. A source of neutrons to initiate the reaction (such as a mixture of polonium and beryllium)
3. A moderator to reduce the energy of fast neutrons for more efficient fission (material such as graphite, beryllium, heavy water, and light water are used)
4. A coolant to remove the fission-generated heat (water, sodium, helium, and nitrogen may be used)
5. A control system such as rods of boron or cadmium that have high capture cross sections (to absorb neutrons)
6. Adequate shielding, remote-control equipment, and appropriate instrumentation are essential for personnel safety and efficient operation.