CHEMISTRY GLOSSARY

electron    →   elektron

The electron is an elementary particle with a negative electric charge of (1.602 189 2±0.000 004 6)×10^-19 C and a mass of 1/1837 that of a proton, equivalent to (9.109 534±0.000 047)×10^-31 kg.

In 1897 the British physicist Joseph John (J.J.) Thomson (1856-1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of bodies much smaller than atoms that he calculated as having a very large value for the charge to mass ratio. Later he estimated the value of the charge itself.

Electrons are arranged in from one to seven shells around the nucleus; the maximum number of electrons in each shell is strictly limited by the laws of physics (2n²). The outer shells are not always filled: sodium has two electrons in the first shell (2×1² = 2), eight in the second (2×2² = 8), and only one in the third (2×3² = 18). A single electron in the outer shell may be attracted into an incomplete shell of another element, leaving the original atom with a net positive charge. Valence electrons are those that can be captured by or shared with another atom.

Electrons can be removed from the atoms by heat, light, electric energy, or bombardment with high-energy particles. Decaying radioactive nuclei spontaneously emit free electrons, called β particles.

gadolinium    →   gadolinij

Gadolinium was discovered by Jean de Marignac (France) in 1880. Named after the mineral gadolinite, named for J. Gadolin, a Finnish chemist and mineralogist. It is soft, ductile, silvery-white metal. Reacts slowly with water and oxygen. Dissolves in acids. Metal ignites and burns readily. Gadolinium is found with other rare earths in gadolinite and monazite sand. Used in steel alloying agents and the manufacture of electronic components.

gallium    →   galij

Gallium was discovered by Lecoq de Boisbaudran (France) in 1875. The origin of the name comes from the Latin word Gallia meaning France. It is soft, blue-white metal. Stable in air and water. Reacts violently with chlorine and bromine. Gallium is found throughout the crust in minerals like bauxite, germanite and coal. Used in semiconductor production. It us used in making LED’s (light-emitting diodes) and GaAs laser diodes.

germanium    →   germanij

Germanium was discovered by Clemens Winkler (Germany) in 1886. The origin of the name comes from the Latin word Germania meaning Germany. It is greyish-white semi-metal. Unaffected by alkalis and most (except nitric) acids. Stable in air and water. Germanium is obtained from refining copper, zinc and lead. Widely used in semiconductors. It is a good semiconductor when combined with tiny amounts of phosphorus, arsenic, gallium and antimony.

global warming    →   globalno zatopljenje

Global warming or greenhouse effect is an effect occurring in the atmosphere because of the presence of certain gases (greenhouse gases) that absorb infrared radiation. Light and ultraviolet radiation from the sun is able to penetrate the atmosphere and warm the Earth’s surface. This energy is re-radiated as infrared radiation which because of its longer wavelength, is absorbed by such substances as carbon dioxide. The overall effect is that the average temperature of the Earth and its atmosphere is increasing (so-called global Warming). The effect is similar to that occurring in a greenhouse, where light and long-wavelength ultraviolet radiation can pass through the glass into greenhouse but the infrared radiation is absorbed by the glass and part of it is re-radiated into the greenhouse.

The greenhouse effect is seen as a major environmental hazard. Average increases in temperature could change weather patterns and agricultural output. It might also lead to melting of the polar ice caps and a corresponding rise in sea level. Carbon dioxide, from fossil-fuel power stations and car exhausts, is the main greenhouse gas. Other contributory pollutants are nitrogen oxides, ozone, methane, and chloroflourocarbons.

glucose    →   glukoza

Glucose (grape sugar, blood sugar), C₆H₁₂O₆, is an aldohexose (a monosaccharide sugar having six carbon atoms and an aldehyde group). An older common name for glucose is dextrose, after its dextrorotatory property of rotating plane polarized light to the right. Glucose in free (in sweet fruits and honey) or combined form (sucrose, starch, cellulose, glycogen) is is probably the most abundant organic compound in nature. During the photosynthesis process, plants use energy from the sun, water from the soil and carbon dioxide gas from the air to make glucose. In cellular respiration, glucose is ultimately broken down to yield carbon dioxide and water, and the energy from this process is stored as ATP molecules (36 molecules of ATP across all processes).

Naturally occurring glucose is D isomers (OH group on the stereogenic carbon farthest from the aldehyde group, C-5, is to the right in the Fischer projection). Although often displayed as an open chain structure, glucose and most common sugars exist as ring structures. In the α form, the hydroxyl group attached to C-1 and the CH₂OH attached to C-5 are located on opposite sides of the ring. β-glucose has these two groups on the same side of the ring. The full names for these two anomers of glucose are α-D-glucopyranose and β-D-glucopyranose.

indium    →   indij

Indium was discovered by Ferdinand Reich and Hieronymus Theodor Richter (Germany) in 1863. Named after the indicum (colour indigo), the colour it shows in a spectroscope. It is rare, very soft, silver-white metal. Stable in air and water. Dissolves in acids. Metal can ignite and burn. Indium is found in certain zinc ores. Used to coat high speed bearings and as an alloy that lowers the melting point of other metals. Relatively small amounts are used in dental items and in electronic semiconductors.

Gratzel solar cell    →   Gratzelova sunčeva ćelija

Grätzel solar cell is photoelectrochemical cell, developed by Michael Grätzel and collaborators, simulates some characteristics of the natural solar cell, which enables photosynthesis take place. In natural solar cell the chlorophyll molecules absorb light (most strongly in the red and blue parts of the spectrum, leaving the green light to be reflected). The absorbed energy is sufficient to knock an electron from the excited chlorophyll. In the further transport of electron, other molecules are involved, which take the electron away from chlorophyll. In Grätzel cell, the tasks of charge-carrier generation and transport are also assigned to different species.

His device consists of an array of nanometre-sized crystallites of the semiconductor titanium dioxide, welded together and coated with light-sensitive molecules that can transfer electrons to the semiconductor particles when they absorb photons. So, light-sensitive molecules play a role equivalent to chlorophyll in photosynthesis. In Grätzel cell, the light-sensitive molecule is a ruthenium ion bound to organic bipyridine molecules, which absorb light strongly in the visible range; titanium dioxide nanocrystals carry the received photoexcited electrons away from electron donors. On the other hand, a donor molecule must get back an electron, so that it can absorb another photon. So, this assembly is immersed in a liquid electrolyte containing molecular species (dissolved iodine molecules) that can pick up an electron from an electrode immersed in the solution and ferry it to the donor molecule. These cells can convert sunlight with efficiency of 10 % in direct sunlight and they are even more efficient in diffuse daylight.

invert sugar    →   invertni šećer

Invert sugar is a mixture of equal parts of glucose and fructose resulting from the hydrolysis of sucrose (saccharose). The name stemming from the fact that it rotates of plane polarized light in the opposite direction of sucrose. Sucrose is dextrorotatory - it rotates polarized light clockwise ([α]_D = +66.5°). Invert sugar rotates the plane of the polarized light counterclockwise ([α]_D = -22°) due to the strongly levorotatory nature of fructose ([α]_D = -92°).

Homemade artificial honey (invert sugar syrup): Dissolve two parts of household sugar (1 kg) with stirring in one part of water (0.5 kg) in a saucepan over low heat. Add 1 g of citric acid or the juice of one lemon to the mixture. Bring the ingredients to a slow boil. It can take anywhere between 15 minutes to 1 hour. The end result is sticky, golden syrup. Let it sit at room temperature until it is cool.

lanthanum    →   lantan

Lanthanum was discovered by Carl Gustaf Mosander (Sweden) in 1839. The origin of the name comes from the Greek word lanthanein meaning to lie hidden. It is soft, silvery-white, malleable, ductile metal. Readily tarnishes in air. Reaction with water releases hydrogen gas. Metal ignites and burns readily. Reacts with oxidants. Lanthanum is found with rare earths in monazite and bastnasite. Monazite sand typical contains 25 % lanthanum. It is used in the electrodes of high-intensity, carbon-arc lights. Because it gives glass refractive properties, it is used in expensive camera lenses.