CHEMISTRY GLOSSARY

chemical equation    →   kemijska jednadžba

Chemical equation is a way of denoting a chemical reaction using the symbol for the participating particles (atoms, molecules, ions, etc.); for example,

The single arrow is used for an irreversible reaction; double arrows are used for reversible reactions. When reactions involve different phases, it is usual to put the phase in brackets after the symbol.

The numbers a, b, c, and d, showing the relative numbers of molecules reacting, are called the stoichiometric coefficients. The convention is that stoichiometric coefficients are positive for reactants and negative for products. If the sum of the coefficients is zero, the equation is balanced.

cosmic rays    →   kozmičke zrake

Cosmic rays are high energy (10¹⁵ eV- 10¹⁷ eV) nuclear particles, electrons, and photons, originating mostly outside the solar system, which continually bombard the Earth’s atmosphere.

curium    →   kurij

Curium was discovered by Glenn T. Seaborg, Ralph A. James and Albert Ghiorso (USA) in 1944. Named in honour of Pierre and Marie Curie. It is silvery, malleable, synthetic radioactive metal. So radioactive it glows in the dark. Curium was made by bombarding plutonium with helium ions.

diffusion current    →   difuzijska struja

Diffusion current (i_d) is a current which is limited by the speed of particle diffusion in an electrolyte solution.

colloid    →   koloid

Colloids are systems in which there are two or more phases, with one (the dispersed phase) distributed in the other (the continuous phase). Moreover, at least one of the phases has small dimensions, in the range between 1 nm and 1 μm (10^-9 m – 10^-6 m). Dimension, rather than the nature of the material, is characteristic. In this size range, the surface area of the particle is large with respect to its volume so that unusual phenomena occur, e.g., the particles do not settle out of the suspension by gravity and are small enough to pass through filter membranes. Macromolecules (proteins and other high polymers) are at the lower limit of this range; the upper limit is usually taken to be the point at which the particles can be resolved in an optical microscope.

Colloidal particles may be gaseous, liquid, or solid, and occur in various types of suspensions:

Sols - dispersions of small solid particles in a liquid.

Emulsions - colloidal systems in which the dispersed and continuous phases are both liquids.

Gels - colloids in which both dispersed and continuous phases have a three-dimensional network throughout the material.

Aerosols - colloidal dispersions of liquid or solid particles in a gas.

Foams - dispersions of gases in liquids or solids.

colloid ion    →   koloidni ion

Colloid ions emerge when colloid particles adsorb certain type of ion from solution and thus become charged with the same charge. The charge can also originate form a chemical reaction of colloid particle’s surface. Colloid ions formed by absorption of silver chloride particle can be show as follows:

Adsorbed layer is monomolecular (one molecule thick) and which type of ion will be formed depends upon which ions are present in a greater number in the solution in. Because of this colloid particles are charged with the same charge, mutual repelling occurs, and the colloid solution becomes stable. Colloid charge can be determined by electrophoresis.

condensation    →   kondenzacija

1. Condensation is a process of changing from a gaseous to a liquid or solid state, usually done by cooling.

2. Condensation, in colloid systems, is a process where smaller particle join in one colloid size particle

3. Condensation, in chemical terms, is a sort of chemical reaction in which small molecules like water, carbon dioxide, or ammonia single out.

digestion    →   digeriranje

Digestion or precipitate ageing happens when freshly formed precipitate are left, usually at a higher temperature, in a solution from which it is precipitated. It results in cleaner and bigger particles.

dissolved substance    →   otopljena tvar

Dissolved substance is a solid, liquid or gas matter dissolved in a solvent. Depending upon the particle size of dissolved substance, solutions differ in properties and can be divided into real solutions (diameter of particles is smaller than 1 nm), colloid solutions (diameter of particles is from 1 nm to 200 nm) and suspensions (diameter of particles is greater than 200 nm).

Dalton’s atomic theory    →   Daltonova atomska teorija

Dalton’s atomic theory is a theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates:

1. Elements consist of indivisible small particles (atoms).

2. All atoms of the same element are identical; different elements have different types of atom.

3. Atoms can neither be created nor destroyed.

4. ’Compound elements’ (i.e. compounds) are formed when atoms of different elements join in simple ratios to form ’compound atoms’ (i.e. molecules).

Dalton also proposed symbols for atoms of different elements (later replaced by the present notation using letters).