CHEMISTRY GLOSSARY

pascal    →   paskal

Pascal (Pa) is the SI derived unit of pressure. One pascal is the pressure generated by a force of one newton acting on an area of one square metre (Pa = N/m²). It was named after the French mathematician, physicist and philosopher Blaise Pascal (1623-1662).

tesla    →   tesla

Tesla (T) is the SI derived unit of magnetic flux density. The tesla is magnetic flux density of a magnetic flux of one weber per square metre (T = Wb/m²). The unit was named after the Croatian scientist Nikola Tesla (1857-1943), equal to V s/m².

Graham’s law    →   Grahamov zakon

Graham’s law is the rates at whish gases diffuse are inversely proportional to the square roots of their densities. This principle is made use of in the diffusion method of separating isotopes. The law was formulated in 1829 by British chemist Thomas Graham (1805-1869).

octahedral molecular geometry    →   oktaedarska geometrija molekule

Octahedral molecular geometry (square bipyramidal shape) describes the shape of compounds where six atoms or ligands are symmetrically arranged around a central atom. The sulfur hexafluoride (SF₆), with six bonding pairs, is predicted and found to be a regular octahedron. Four of the attachments are positioned in a square plane with 90° bond angles. The remaining two attachments are positioned perpendicular (90°) to the square plane at opposite ends of the central atom. Molecules with an octahedral electron pair geometries have sp³d² (or d²sp³) hybridization at the central atom.

paper chromatography    →   papirna kromatografija

Paper chromatography is one of the types of chromatography procedures which runs on a piece of specialized paper. It is a planar chromatography systems wherein a cellulose filter paper acts as a stationary phase on which separation of compounds occurs. The edge of the paper is immersed in a solvent, and the solvent moves up the paper by capillary action.

Newton’s gravitational law    →   Newtonov zakon gravitacije

Every object in the universe attracts every other object with a force (gravitational force F_G) directed along the line through centres of the two objects that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

m₁ and m₂ are masses of the two objects and r is the distance between them. G is universal constant of gravitation, which equals 6.67•10^-26 N m² kg^-2. Strictly speaking, this law applies only to objects that can be considered pointlike object. Otherwise, the force has to be found by integrating the forces between various mass elements.

It is more properly to express Newton’s gravitational law by vector equation:

in which r₁ and r₂ are position vectors of masses m₁ and m₂.

Gravitational forces act on distance. Newton’s gravitational law is derived from Kepler’s law for planetary motion, using a physical assumption considering Sun as the centre and the source of gravitational force.

Additionally, every object moves in the direction of the force acting on it, with acceleration that is inversely proportional to the mass of object. For bodies on the surface of Earth, the distance r in gravitational law formula is practically equal to the Earth radius, R_E. If the mass of the body on Earth surface is m and the mass of earth is M_E, the gravitational force acting on that body can be expressed as:

where g is gravitational acceleration which is, although dependent on geographical latitude, usually considered as constant equal to 9.81 m s^-2.

porphyrin    →   porfirin

Porphyrin is a planar ligand with a central ring structure and various substituent groups at the edges of the ring.

retardation factor    →   faktor zaostajanja

Retardation factor, R_F, (in planar chromatography) is a ratio of the distance travelled by the centre of the spot to the distance simultaneously travelled by the mobile phase:

The R_F value is characteristic for any given compound on the same stationary phase using the same mobile phase for development of the plates. Hence, known R_F values can be compared to those of unknown substances to aid in their identifications.

second-order reactions    →   reakcije drugog reda

Second-order reaction is a reaction with a rate law that is proportional to either the concentration of a reactant squared, or the product of concentrations of two reactants.

For a general unimolecular reaction,

The reaction rate expression for a second order reaction is

If assumed that the concentration of reactant A is [A]_o at t=0 and [A] at time T, the variables in the rate equation and integrate can be separated. The integrated rate law for a second-order reaction can be easily shown to be