CHEMISTRY GLOSSARY

base-centered monoclinic lattice    →   bazno centrirana monoklinska rešetka

Base-centered or side-centered or end-centered monoclinic lattice (monoclinic-C), like all lattices, has lattice points at the eight corners of the unit cell plus additional points at the centers of two parallel sides of the unit cell. It has unit cell vectors a≠b≠c, and interaxial angles α=γ=90°≠β.

base-centered orthorhombic lattice    →   bazno centrirana ortorompska rešetka

Base-centered or side-centered or end-centered monoclinic lattice (orthorhombic-C), like all lattices, has lattice points at the eight corners of the unit cell plus additional points at the centers of two parallel sides of the unit cell. It has unit cell vectors a≠b≠c and interaxial angles α=β=γ=90°.

weak electrolyte    →   slabi elektrolit

Weak electrolytes are those electrolytes which in water solutions dissociate only partially, giving ions and which are in equilibrium with undissociated molecules. Their water solutions conduct electric current weakly. For example, acetic acid partially dissociates into acetate ions and hydrogen ions, so that an acetic acid solution contains both molecules and ions.

acid    →   kiselina

Acid is a type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction for an acid HA is commonly written:

In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:

This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and produce colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water, (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. acetic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant.

In the Lowry-Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). An important feature of the Lowry-Brønsted concept is that when an acid gives up a proton, a conjugate base is formed that is capable of accepting a proton.

Similarly, every base produces its conjugate acid as a result of accepting a proton.

For example, acetate ion is the conjugate base of acetic acid, and ammonium ion is the conjugate acid of ammonia.

As the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa.

A further extension of the idea of acids and bases was made in the Lewis theory. In this, a G. N. Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses "traditional" acid-base reactions, but it also includes reactions that do not involve ions, e.g.

in which NH₃ is the base (donor) and BCl₃ the acid (acceptor).

buffer    →   pufer otopina

Buffer is a solution designed to maintain a constant pH when small amounts of a strong acid or base are added. Buffers usually consist of a fairly weak acid and its salt with a strong base. Suitable concentrations are chosen so that the pH of the solution remains close to the pK_a of the weak acid.

primary amine    →   primarni amin

Primary amine is an amine on which there is only one alkyl group bonded, it is a weak base, and has a fish odour.

acetylene    →   acetilen

Acetylene (ethyne) is a colourless unstable gas, C₂H₂, with a characteristic sweet odour. It is lighter than air, easily soluble in acetone (propanone) and it is explosive under high pressure.

alkaloid    →   alkaloid

Alkaloids are basic nitrogen organic compounds (mostly heterocyclic) derived from plants and having diverse pharmacological properties. Alkaloids include morphine, cocaine, atropine, quinine, and caffeine, most of which are used in medicine as analgesics or anaesthetics. Some alkaloids are poisonous, e.g. strychnine and coniine, and colchicine inhibit cell division.

amino acids    →   aminokiseline

Amino acids are compounds containing both a carboxylic acid group (-COOH) and an amino group (-NH₂ ). The most important are the α-amino acids, in which the -NH₂ group in attached to the C atom adjacent to the -COOH group. In the β-amino acids, there is an intervening carbon atom.

alkali metal    →   alkalijski metal

Alkali metal is a term that refers to six elements: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). These elements make up group 1 of the periodic table of elements. They all form singly charged positive ions, and are extremely reactive. They react violently with water, forming hydroxides and releasing hydrogen gas and heat. Caesium and francium are the most reactive and lithium is the least.