CHEMISTRY GLOSSARY

carbohydrate    →   ugljikohidrat

Carbohydrates (often called carbs for short) are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. They are also known as saccharides, a term derived from the Latin word saccharum for sugar. Carbohydrates are the most abundant class of compounds in the biological world, making up more than 50 % of the dry weight of the Earth’s biomass. Every type of food we eat can have its energy traced back to a plant. Plants use carbon dioxide and water to make glucose, a simple sugar, in photosynthesis. Other carbohydrates such as cellulose and starch are made from the glucose. Light from the sun is absorbed by chlorophyll and this is converted to the energy necessary to biosynthesize carbohydrates

The term carbohydrate was applied originally to monosaccharides, in recognition of the fact that their empirical composition can be expressed as C_x(H₂O)_y. Later structural studies revealed that these compounds were not hydrates but the term carbohydrate persists.

Carbohydrates are generally classed as either simple or complex. Simple sugars, or monosaccharides, are carbohydrates that can’t be converted into smaller subunits by hydrolysis. Complex carbohydrates are made of two (disaccharides) or more (oligosaccharides, polysaccharides) simple sugars linked together by acetal (glycosidic) bonds and can be split into the former by hydrolysis.

Einstein, Albert    →   Einstein, Albert

Albert Einstein (1879-1955) is a German born American physicist, who took Swiss nationality in 1901. A year later he went to work in the Bern patent office. In 1905. he published five enormously influential papers, one on Brownian movement, one on the photoelectric effect, one on the special theory of relativity, and one on energy and inertia (which included the famous expression E = mc²). In 1915 he published the general theory of relativity, concerned mainly with gravitation. In 1921 he was awarded the Nobel Prize. In 1933, as a Jew, Einstein decided to remain in the USA (where he was lecturing), as Hitler had come to power. For the remainder of his life he sought a unified field theory. In 1939 he informed president Roosevelt that an atom bomb was feasible and that. Germany might be able to make one.

radiography    →   radiografija

Radiography is nondestructive method of internal examination in which metal objects are exposed to a beam of X-ray or gamma radiation. Differences in thickness, density, or absorption caused by internal defects or inclusions are apparent in the shadow image produced on a fluorescent screen or photographic film placed behind the object.

wave-particle duality    →   valno-čestična dualnost

Wave-particle duality is an observation that electrons, photons, and other very small entities behave like particles in some experiments and like waves in others.

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.

Geiger counter    →   Geigerov brojač

Geiger counter (Geiger-Muller counter) is a device used to detect and measure ionising radiation. It consists of a tube containing a low-pressure gas (usually argon or neon with methane) and a cylindrical hollow cathode through the centre of which runs a fine-wire anode. A potential difference of about 1 000 V is maintained between the electrodes. An ionising particle or photon passing through a window into the tube will cause an ion to be produced and the high potential will accelerate it towards its appropriate electrode, causing an avalanche of further ionisations by collision. The consequent current pulses can be counted in electronic circuits or simply amplified to work a small loudspeaker in the instrument. It was first devised in 1908 by the German physicist Hans Geiger (1882-1945). Geiger and W. Muller produced an improved design in 1928.

luminescence    →   luminiscencija

Luminescence (from Latin lumen, light) is the emission of electromagnetic radiation (UV, visible or IR) from atoms or molecules as a result of the transition of an electronically excited state to a lower energy state, usually the ground state. Luminescence can be divided into categories by duration (fluorescence or phosphorescence) or by the mechanism that creates the light (radioluminescence, electroluminescence, photoluminescence, thermoluminescence, triboluminescence, chemiluminescence, bioluminescence). The prefix identifies the energy source responsible for generating or releasing the light.

Phosphorescence is emission of light from a substance exposed to radiation and persisting as an afterglow after the source of excitation has been removed. Fluorescence, on the other hand, is an almost instantaneous effect, ending within about 10^-8 second after excitation.

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.

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.

potassium    →   kalij

Potassium was discovered by Sir Humphry Davy (England) in 1807. The origin of the name comes from the Arabic word qali meaning alkali (the origin of the symbol K comes from the Latin word kalium). It is soft, waxy, silver-white metal. Fresh surface has silvery sheen. Quickly forms dull oxide coating on exposure to air. Reacts strongly with water. Reacts with water to give off flammable gas. Reacts violently with oxidants. Occurs only in compounds. Potassium is found in minerals like carnallite [(KMgCl₃)·6H₂O] and sylvite (KCL). Pure metal is produced by the reaction of hot potassium chloride and sodium vapours in a special retort. Used as potash in making glass and soap. Also as saltpetre, potassium nitrate (KNO₃) to make explosives and to colour fireworks in mauve. Vital to function of nerve and muscle tissues.