CHEMISTRY GLOSSARY

trigonal pyramidal molecular geometry    →   trigonska piramidalna geometrija molekule

Trigonal pyramidal is a molecular shape that results when there are three bonds and one lone pair on the central atom in the molecule. Molecules with an tetrahedral electron pair geometries have sp³ hybridization at the central atom. Ammonia (NH₃) is a trigonal pyramidal molecule.

triple bond    →   trostruka veza

Triple bond. (≡) is a covalent bond that involves 3 bonding pairs. In the valence bond theory, one of the bonds in a triple bond is a sigma bond and the other two are pi bonds. For example, the central bond in acetylene is a triple bond: H-C≡C-H.

U-tube    →   U-cijev

U-tube filled with a sodium hydroxide is used for a cleaned and dried gas.

U-tube filled with a 1 mol dm^-3 aqueous potassium nitrate solution is used as a permanent salt bridge.

U-tube is a device used for water electrolysis, for laboratory hydrogen and oxygen obtaining.

ultraviolet light    →   ultraljubičasto svjetlo

Ultraviolet light (UV light or UV radiation) is an electromagnetic radiation with a wavelength longer than that of x-rays, but shorter than that of visible light. Ultraviolet light can break some chemical bonds and cause cell damage.

visible radiation    →   vidljivo zračenje

Human eye can only see electromagnetic radiation of wavelengths form 400 nm to 760 nm. This narrow part of electromagnetic spectrum is called visible radiation. Visible (white) light is a mixture of light of all kind of colours, it can be separated, with the help of a glass prism, into its component colours - visible light spectrum, and each colour corresponds to a certain area of wavelengths:

Volta, Alessandro    →   Volta, Alessandro

The Italian physicist Alessandro Giuseppe Antonio Anastasio Volta (1745-1827) was the inventor of the voltaic pile, the first electric battery (1800). In 1775 he invented the electrophorus, a device that, once electrically charged by having been rubbed, could transfer charge to other objects. Between 1776 and 1778, Volta discovered and isolated methane gas (CH₄). The electrical unit known as the volt was named in his honor.

work    →   rad

Work is the energy required to move an object against an opposing force. Work is usually expressed as a force times a displacement.

When a constant force F acts on a point-like object while the object moves through a displacement s, the force does work W on the object. If force and displacement are at a constant angle Θ to each other, the work is expressed by the scalar product of these two vectors:

When the force F on a point-like object is not constant that is, it depends on the position of the object, the work done by force while object moves from initial position with coordinates (x_i, y_i, z_i) to final position with coordinates (x_f, y_f, z_f)is given by expression:

Where F_x, F_y and F_z are scalar components of the force.

SI unit for work is joule (J); 1 J = 1 Nm = 1 kg m² s^-2. The electron-volt (eV) is commonly used in atomic and nuclear physics.

X-ray tube    →   rendgenska cijev

X-ray tube is a cathode ray tube that focuses energetic streams of electrons on a metal target, causing the metal to emit X-rays. The basic principle of the X-ray tube has not changed significantly since Roentgen's 1895 discovery. Current applied to a metal cathode (about 50 000 V) produces free electrons. The X-rays are produced when the rapidly moving electrons are suddenly stopped as they strike the metal target of the tube.

Heyrovsky-Ilkovic equation    →   Heyrovsky-Ilkovičeva jednadžba

The Heyrovsky-Ilkovic equation describes the entire current-potential curve (polarographic wave) of a reversible redox system in polarography

where R is the gas constant, T is the absolute temperature, F is the Faraday constant, n denotes the number of electrons taking part in the electrode reaction. E_1/2 is a unique potential (for a given reaction and supporting electrolyte) termed the half-wave potential.

In order to obtain E_1/2 from the above equation, we plot a graph of ln[(i_d-i)/i] against E. The intercept on the x-axis gives then an accurate value of E_1/2. The slope of the obtained straight line is equal to nF/RT from which n is determined.