CHEMISTRY GLOSSARY

Born-Haber cycle    →   Born-Haberov kružni proces

Born-Haber cycle is a cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction

The standard enthalpy of formation of the ionic solid is the enthalpy of the reaction

The cycle involves equating this enthalpy (which can be measured) to the sum of the enthalpies of a number of steps proceeding from the elements to the ionic solid. The steps are:

1) Atomization of the metal

2) Atomization of the nonmetal

3) Ionisation of the metal

This is obtained from the ionisation potential.

4) Ionisation of the nonmetal

This is electron affinity.

5) Formation of the ionic solids

Equation of the enthalpies gives

from which ΔH_L can be found.

osmometry    →   osmometrija

Osmometry is a determination of the average molecular weight of a dissolved substance from measurements of osmotic pressure.

quasicrystal    →   kvazikristal

Quasicrystal is a solid having conventional crystalline properties but whose lattice does not display translational periodicity.

white light    →   bijela svjetlost

White light is a mixture of lights of all colours. If white light is passed through a glass prism or an optical lattice, it is separated into several colours (the visible light spectrum).

Bragg angle    →   Braggov kut

Bragg angle (Θ) is the angle between an incident X-ray beam and a set of crystal planes for which the secondary radiation displays maximum intensity as a result of constructive interference. British physicist Sir William Henry Bragg and his son Sir William Lawrence Bragg developed a simple relation for scattering angles, now call Bragg’s law.

which relates the angle θ between a crystal plane and the diffracted X-ray beam, the wavelength λ of the x-rays, the crystal plane spacing d, and the diffraction order n (any integer).

The diffraction experiment as presently considered is intended to provide quantitative information on the lattice constant and shape characteristics of the unit cell.

Curie temperature    →   Curiejeva temperatura

For a ferromagnetic material, Curie temperature or Curie point (T_C) is the critical temperature above which the material becomes paramagnetic. For iron the Curie point is 760 °C and for nickel 356 °C. It was named after the French physicist Pierre Curie (1859-1906).

cysteine    →   cistein

Cysteine is neutral amino acids with polar side chains. Because of its high reactivity, the thiol group of cysteine has numerous biological functions. It serves as a potent nucleophile and metal ligand (particularly for iron and zinc), but is best known for its ability to form disulfide bonds, which often make an important contribution to the stability of extracellular proteins. Cysteine is a non-essential amino acid, which means that it is biosynthesized in humans.

• Abbreviations: Cys, C
• IUPAC name: 2-amino-3-sulfanylpropanoic acid
• Molecular formula: C₃H₇NO₂S
• Molecular weight: 121.16 g/mol

free radical    →   slobodni radikal

Free radical is a molecular fragment having one or more unpaired electrons, usually short-lived and highly reactive. They can be produced by photolysis or pyrolysis in which a bond is broken without forming ions. In formulas, a free radical is conventionally indicated by a dot (·CH₃, ·SnH₃, ·Cl). Free radicals are known to be formed by ionising radiation and thus play a part in deleterious degradation effects that occur in irradiated tissue. They also act as initiators or intermediates in oxidation, combustion, photolysis, and polymerisation.

fructose    →   fruktoza

Fructose (fruit sugar) is a ketohexose (a six-carbon ketonic sugar), which occurs in sweet fruits and honey. Glucose and fructose have the same molecular formula, C₆H₁₂O₆, but have different structures. Pure, dry fructose is a very sweet, white, odorless, crystalline solid. Fructose is one of the sweetest of all sugars and is combined with glucose to make sucrose, or common table sugar. An older common name for fructose is levulose, after its levorotatory property of rotating plane polarized light to the left (in contrast to glucose which is dextrorotatory). The polysaccharide inulin is a polymer of fructose.

glass electrode    →   staklena elektroda

Glass electrode is a hydrogen-ion responsive electrode usually consisting of a bulb, or other suitable form, of special glass attached to a stem of high resistance glass complete with internal reference electrode and internal filling solution system. Glass electrode is also available for the measurement of sodium ions.

The glass electrode, which consists of a thin wall glass bulb, has an extremely high electrical resistance. The membrane of a typical glass electrode (with a thickness of 0.03 mm to 0.1 mm) has an electrical resistance of 30 MΩ to 600 MΩ. The surface of a glass membrane must be hydrated before it will function as a pH electrode. When a glass surface is immersed in an aqueous solution then a thin solvated layer (gel layer) is formed on the glass surface in which the glass structure is softer. This applies to both the outside and inside of the glass membrane.

The simplest explanation for the working of the thin glass electrode is that the glass acts as a weak acid (Glass-H).

The hydrogen ion activity of the internal solution is held constant. When a solution of different pH from the inside comes in contact with the outside of the glass membrane, the glass is either deprotonated or protonated relative to the inside of the glass. The difference in pH between solutions inside and outside the thin glass membrane creates electromotive force in proportion to this difference in pH.