الرئيسية » Simplified Chemistry (صفحه 6)

Simplified Chemistry

Azeotropic distillation

Azeotropic distillation Any of several processes by which liquid mixtures containing azeotropes may be separated into their pure components with the aid of an additional substance (called the entrainer, the solvent, or the mass separating agent) to facilitate the distillation. Distillation is a separation technique that exploits the fact that …

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Avogadro’s law

Avogadro’s law The principle that equal volumes of all gases and vapors, under the same conditions of temperature and pressure, contain identical number of molecules; also known as Avogadro’s hypothesis. From Avogadro’s law the converse follows that equal numbers of molecules of any gases under identical conditions occupy equal volumes. …

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Atropine

Atropine An alkaloid, C17H23NO3, with the chemical structure below. The sys­tematic chemical name is endo-(±)-a-(hydroxymethyl) phenylacetic acid 8-methyl- 8-azabicyclo[3.2.l]oct-3-yl ester, and in phamacy it is sometimes known as dl­hyoscyamine. It occurs in minute amounts in the leaves of Atropa belladonna, A. betica, Datura stramonium, D. innoxia, and D. sanguinea, as …

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Atomic structure and spectra

Atomic structure and spectra The idea that matter is subdivided into discrete and further indivisible building blocks called atoms dates back to the Greek philosopher Democritus, whose teachings of the 5th century B.C. are commonly ac­cepted as the earliest authenticated ones concerning what has come to be called atom­ism by …

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Atomic spectrometry

Atomic spectrometry A branch of chemical analysis that seeks to deter­mine the composition of a sample in terms of which chemical elements are present and their quantities or concentrations. Unlike other methods of elemental analysis, however, the sample is decomposed into its constituent atoms which are then probed spectroscopically. In …

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Atomic number

Atomic number The number of elementary positive charges (protons) con­tained within the nucleus of an atom. It is denoted by the letter Z. Correspondingly, it is also the number of planetary electrons in the neutral atom. The concept of atomic number emerged from the work of G. Moseley, done in …

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Atomic nucleus

Atomic nucleus The central region of an atom. Atoms are composed of nega­tively charged electrons, positively charged protons, and electrically neutral neutrons. The protons and neutrons (collectively known as nucleons) are located in a small central region known as the nucleus. The electrons move in orbits which are large in …

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Atomic mass unit

Atomic mass unit An arbitrarily defined unit in terms of which the masses of individual atoms are expressed. One atomic mass unit is defined as exactly 1fi2 of the mass of an atom of the nuclide 12C, the predominant isotope of carbon. The unit, also known as the dalton, is …

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Atom

Atom A constituent of matter consisting of z negatively charged electrons bound predominantly by the Coulomb force to a tiny, positively charged nucleus consisting of Z protons and (A – Z) neutrons. Z is the atomic number, and A is the mass or nucleon number. The atomic mass unit is …

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Art conservation chemistry

Art conservation chemistry The application of chemistry to the technical examination, authentication, and preservation of cultural property. Chemists working in museums engage in a broad range of investigations, most frequently studying the chemical composition and structure of artifacts, their corrosion products, and the ma­terials used in their repair, restoration, and …

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