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Home >> Chemistry Dictionary >> Band Spectrum - Barometer
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Banana bond.
Informal name for the type of electron deficient bond which is holding the B-H-B bridges in boranes and similar compounds.
Band Spectrum.
The absorption of energy by a molecule may lead to the transition of an electron from an orbital of lower t one of higher energy (see line spectrum), but in addition there may be an increase in the energy of rotation of the molecule as a whole, and in the energy of vibration of the constituent atoms relative to each other. The simultaneous occurrence of these changes gives rise to many possible energy changes. The resulting spectrum is correspondingly complicated, and consists of numerous very closely spaced lines. The frequency of a line is determined by the algebraic sum of the energy change involved. An electronic transition is associated with so much more energy than vibration and rotational changes that it determines the general position of the line in the spectrum. The spectrum thus consist of well-defined group or bands, of closely packed lines. Such a spectrum characteristic of a molecule, is termed a band spectrum.
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Bans theory of solids.
In molecules, molecular orbital arise by combination of atomic orbitals. The ideals of delocalized electron can also be applied to large assemblies of atoms in solids. The quantum mechanical treatment of these electrons gives rise to the band theory of solids, in which there are bands of electron levels, sometimes over lapping, e.g. metals, sometimes with a forbidden energy gap, e.g. insulator oxides, between them.
Bar.
A unit of pressure used particularly at higher pressure.1 bar = 105Nm-2.1 bar ≈ 1 atm.
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Barbitone, diethylmalonylurea,
C8H12N2O3 White crystals, m.p. 191°C. A barbituric acid derivative. The sodium salt is administered orally as a sedative.
Barfoed’s test.
A biochemical test which is used to detect monosaccharide sugar in solution. Barfoed’s reagent, a mixture of ethanoic acid and copper acetate, is added to the test solution and boiled. If any reducing sugars are present, a red precipitate of copper oxide gets produced. The reaction will be negative in the presence of disaccharide sugar as they have been weaker reducing agents.
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Barite.
BaSO4. Natural barium sulphate. Transparent barite crystals are used in optical instrument, employed as protection from X-ray, as a material for coatings in the chemical industry.
Barium.
Ba. At.no. 56 at wt. 137.33, m.p. 725°C, d 3.51. An alkaline earth occurring principally as BaSO4(barytes) and as BaCO3(whiterite, alstonite). The metal (bcc) is prepared by electrolysis of fused BaCl2 or BaCl2 plus Na. It is silver white in colour, oxidizes easily in air. Used as a getter for oxygen removal. Ba salts find extensive use, BaSO4 used in paints (lithopone), X-rays diagnosis glass, oil well drilling fluids: BaCO3 as a rat poison. Ba compounds are poisonous.
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Barium carbonate.
BaCO3. A white crystalline solid occurring native (witherite) or prepared from a soluble Ba salt and Na2CO3.
Barium Chromate,
BaCrO4. A yellow pigment (Ba salt plus Na2CrO4) rather insoluble in water.
Barium diphenylamine-r-sulphonate.
A redox indicator, used particularly in CrO42-/Ee2+ titrations. In the oxidized from the indicator, is deep reddish-violent.
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Barium hydroxide (baryta).
A white solid, Ba(OH)2, sparingly soluble in water. r.d.2.18; m.p. 78°C. It can be produced by adding water to barium monoxide or by the action of sodium hydroxide on soluble barium compounds and is used as a weak alkali in volumetric analysis.
Barium nitrate,
Ba(NO3)2. Colourless barium salt (BaO plus HNO3) soluble in water.
Barium Oxide.
A white or yellowish solid BaO. Barium oxide is now used in the manufacture or lubricating oil additives.
Barium sulphide, black ash,
BaS. Important intermediate in Ba chemistry (BaSO4plus C). Strongly phosphorescent as normally prepared because of the impurities.
Barium titanate,
BaTiO3. An important solid state compound. Piezoelectric, used in transducers, ultrasonics, gramophone pick-ups and for polishing. Prepared from BaCO3 and TiO2 at high temperatures.
Barrel.
A measure of volume widely used in the petroleum industry. A barrel is approximately 0.159 m3 (5.61 ft3) and contains 35 U.K. gallons.
Barometer.
A device for measuring atmospheric pressure in terms of the height of a liquid column sustained by that pressure.
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