Charged atoms

Appealing and important as this concept of a molecule consisting of partially charged atoms has been for many decades for explaining chemical reactivity and discussing reaction mechanisms, chemists have only used it in a qualitative manner, as they can hardly attribute a quantitative value to such partial charges. Quantum mechanical methods (see Section 7.4) as well as empirical procedures (see... 

AMBER. BlO-t-. and OPLS calciilations use information on atomic charges. Atomic charges can come from these sources ... 

Ambident reactivity occurs for any substance displaying protomeric behavior. In basic medium anions in which negative charge is delocalized are formed this may be represented by the resonance formulas in Scheme 2. Each charged atom may react with an electrophilic center. The... 

When two or more structures satisfy the octet rule the most stable one is the one with the smallest separation of oppositely charged atoms... 

Many biological processes involve an associa tion between two species in a step prior to some subsequent transformation This asso ciation can take many forms It can be a weak associ ation of the attractive van der Waals type or a stronger interaction such as a hydrogen bond It can be an electrostatic attraction between a positively charged atom of one molecule and a negatively charged atom of another Covalent bond formation between two species of complementary chemical re activity represents an extreme kind of association It often occurs in biological processes in which aide hydes or ketones react with amines via imine inter mediates... 

The red part of the map identifies oxy gen as a negatively charged atom and the blue part identifies the most posi tively charged hydrogen atom... 

Ylide (Section 17 12) A neutral molecule in which two oppo sitely charged atoms each with an octet of electrons are di rectly bonded to each other The compound... 

For extremely small penetrations a technique may be employed which depends upon the weak penetration of charged atoms with a known absorption law. The a-particles, which are He + ions, have a linear absorption... 

Calculation of the energies and forces due to the long-range Coulomb interactions between charged atoms is a major problem in simulations of biological molecules (see Chapter 5). In an isolated system the number of these interactions is proportional to N-, where N is the number of charged atoms, and the evaluation of the electrostatic interactions quickly becomes intractable as the system size is increased. Moreover, when periodic... 

A SSIMS spectrum, like any other mass spectrum, consists of a series of peaks of dif ferent intensity (i. e. ion current) occurring at certain mass numbers. The masses can be allocated on the basis of atomic or molecular mass-to-charge ratio. Many of the more prominent secondary ions from metal and semiconductor surfaces are singly charged atomic ions, which makes allocation of mass numbers slightly easier. Masses can be identified as arising either from the substrate material itself from deliberately introduced molecular or other species on the surface, or from contaminations and impurities on the surface. Complications in allocation often arise from isotopic effects. Although some elements have only one principal isotope, for many others the natural isotopic abundance can make identification difficult. 

ANION A negatively charged atom or group of atoms, or a radical which moves to the positive pole (anode) during electrolysis. 

The predominant species observed in SIMS spectra are singly charged atomic and molecular ions [51], However, inorganic and organic cluster ions can also be formed. If the sample consists of a simple single-component metal, then clusters such as M, M, etc., are observed in addition to M+ [52], Oxidation of the metal results in formation of MO ", MO/, M Oll", etc. The relative yield of MO+ to M+ depends on the bond dissociation energy of the oxide [52], For a two-component, oxidized metal, clusters of the type M/", M N, MjO, and M N O/ are observed [51]. 

The exact expression for the dipole moment does n( consider atoms as point charges, but rather as nuclei (eat with a positive charge equal to the atomic number) ar electrons (each with unit negative charge). Atoms wii lone pairs may contribute to the dipole moment, even the atom is neutral, as long as the lone pair electrons a not symmetrically placed around the nucleus. 

The favorability of acid-base reactions is affected, in pa by electrostatic interactions between charged atoms a dipoles within the same molecule. The equilibrium w shift in the direction of an ion that is stabilized 1 intramolecular ion-dipole interactions. 

It has recently been suggested that the imino hydrogen atom in 1,2,4-triazoles is not attached to any of the nitrogen atoms but rather that it exists as a charged atom closely bound by a negatively charged triazole nucleus stabilized by resonance (e.g., 34 and 35), but such a representation is considered to be incorrect and misleading by the present authors. 

To generate electrical energy from chemical energy, the reactant molecules must be separated into oppositely charged ions (electrically charged atoms or groups of atoms) and the exothermic reaction (gives... 

Fermi had been fascinated by the discovery of the neutron by James Chadwick in 1932. He gradually switched his research interests to the use of neutrons to produce new types of nuclear reactions, in the hope of discovering new chemical elements or new isotopes of known elements. He had seen at once that the uncharged neutron would not be repelled by the positively-charged atomic nucleus. For that reason the uncharged neutron could penetrate much closer to a nucleus without the need for high-energy particle accelerators. lie discovered that slow neutrons could... 

When feed contacts the regenerated catalyst, the feed vaporizes. Then positive-charged atoms called carbocations are formed. Carbo-cation is a generic term for a positive-charged carbon ion. Carbocations can be either carbonium or carbenium ions. 

In the case of a singly charged atomic ion in aqueous solution we have estimated the mutual potential energy between the ion and an adjacent water molecule when they are of nearly the same size, and have found the value to be about four times as great as the mutual potential energy of two adjacent water molecules. We conclude then that in the vicinity of an atomic ion the water structure will have to build itself round the ion, insofar as this is possible. 

The electrophilic sink must be able to accept an electron pair, usually because it has either a positively charged atom or a positively polarized atom in a functional group, for example ... 

The reactions that we discuss in this chapter will be represented by nuclear equations. An equation of this type uses nuclear symbols such as those written above in other respects it resembles an ordinary chemical equation. A nuclear equation must be balanced with respect to nuclear charge (atomic number) and nuclear mass (mass number). To see what that means, consider an equation that we will have a lot more to say about later in this chapter ... 

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