Simplified Chemistry

 

Atropine

Atropine An alkaloid, C17H23NO3, with the chemical structure below. The sys­tematic chemical name is endo-(±)-a-(hydroxymethyl) phenylacetic acid 8-methyl- 8-azabicyclooct-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 well as many related plants. It is chiefly manufactured by racemization of 1-hyoscyamine, which is isolated from the…

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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 students of Greek philosophy. The weaving of the philosophical thread of atom­ism into the analytical fabric of physics…

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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 routine atomic spectrometry, a device called the atom source or atom cell is responsible for producing atoms from…

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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 1913-1914. He measured the wavelengths of the most energetic rays (Kand L lines) produced by using the elements…

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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 comparison with the dimensions of the nucleus itself. Protons and neutrons possess ap­proximately equal masses, each roughly 1840…

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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 often abbreviated amu, and is designated by the symbol u. The relative atomic mass of a…

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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 u = 1.6605397 x 10-24 g. Electrically neutral atoms (z = Z) with the range Z = 1…

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Astatin

Astatine A chemical element, At, atomic number 85. Astatine is the heaviest of the halogen groups, filling the place immediately below iodine in group 17 of the periodic table. Astatine is a highly unstable element existing only in short-lived radioactive forms. About 25 isotopes have been prepared by nuclear reactions of artificial transmutation. The longest-lived of these is 210At, which decays with a half-life of only 8.3 h….

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Aspartame

Aspartame A white, crystalline compound, 1-aspartyl-1-phenylalanine methyl ester (APM), with formula as shown in the figure. It is slightly soluble in water. Its sweetening pro­perties were discovered accidentally in 1965 when the compound, a dipeptide, was produced as an intermediate in the synthesis of the C-terminal tetrapeptide of gastrin. Aspartame is the L,L-diastereoisomer; the three other possible diastereoiso­mers are not…

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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 conservation. The effects of the museum environment, including air pollutants, fluctuations in temperature and relative humid­ity, biological activity,…

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