Polyatomic ion

Summary

A polyatomic ion (also known as a molecular ion) is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. The term molecule may or may not be used to refer to a polyatomic ion, depending on the definition used. The prefix poly- carries the meaning "many" in Greek, but even ions of two atoms are commonly described as polyatomic. In older literature, a polyatomic ion may instead be referred to as a radical (or less commonly, as a radical group). In contemporary usage, the term radical refers to various free radicals, which are species that have an unpaired electron and need not be charged. A simple example of a polyatomic ion is the hydroxide ion, which consists of one oxygen atom and one hydrogen atom, jointly carrying a net charge of −1; its chemical formula is . In contrast, an ammonium ion consists of one nitrogen atom and four hydrogen atoms, with a charge of +1; its chemi

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Degradation mechanism of slag blended mortars immersed in sodium sulfate solution

Karen Scrivener, Wei Sun, Cheng Yu

Additions of slag are usually considered to give cementitious materials which perform well in sulfate bearing environments. This paper compares the deterioration of slag cement blends to those of plain Portland cement and demonstrates that this occurs more through loss of surface than macroscopic expansion. When slag blended mortar is immersed in sodium sulfate solution, the sulfate ions penetrating into samples are mostly fixed by aluminate phases in a relatively narrow region close to surface, due to the refinement of pore size and buffering effect by slag addition. After all available aluminate phases have been reacted, the concentration of sulfate ion in pore solution will increase. Once the solution concentration reaches a critical level, fine AFm crystals confined within the C-S-H can react to form ettringite, exerting expansion force. If the system contains sufficient confined AFm phases, this process can cause spalling of the surface layer. Then, sulfate ions can penetrate into the sound area, manifesting another expansive area. Furthermore, the penetration depth of slag sample does not depend strongly on the concentration of sulfate solution, but higher concentration increases the crystallization pressure of ettringite, thereby causing more damage. (C) 2015 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2015

Resonances are among the clearest quantum mechanical signatures of scattering processes. Previously, shape resonances and Feshbach resonances have been observed in inelastic and reactive collisions involving atoms or diatomic molecules. Structure in the integral cross section has been observed in a handful of elastic collisions involving polyatomic molecules. The present paper presents the observation of shape resonances in the reactive scattering of a polyatomic molecule, NH3. A merged-beam study of the gas phase He(S-3(1)) + NH3 Penning ionization reaction dynamics is described in the collision energy range 3.3 mu eV < E-coll < 10 meV. In this energy range, the reaction rate is governed by long-range attraction. Peaks in the integral cross section are observed at collision energies of 1.8 meV and 7.3 meV and are assigned to l = 15,16 and l = 20,21 partial wave resonances, respectively. The experimental results are well reproduced by theoretical calculations with the short-range reaction probability P-sr = 0.035. No clear signature of the orbiting resonances is visible in the branching ratio between NH3+ and NH2+ formation. (C) 2015 AIP Publishing LLC.

American Institute of Physics2015

The H2O+ radical ion, produced in an electrospray ion source via charge transfer from Eu3+, is encapsulated in benzo-15-crown-5 (B15C5) or benzo-18-crown-6 (B18C6). We measure UV photodissociation (UVPD) spectra of the (H2O·B15C5)+ and (H2O·B18C6)+ complexes in a cold, 22-pole ion trap. These complexes show sharp vibronic bands in the 35 700–37 600 cm–1 region, similar to the case of neutral B15C5 or B18C6. These results indicate that the positive charge in the complexes is localized on H2O, giving the forms H2O+·B15C5 and H2O+·B18C6, in spite of the fact that the ionization energy of B15C5 and B18C6 is lower than that of H2O. The formation of the H2O+ complexes and the suppression of the H3O+ production through the reaction of H2O+ and H2O can be attributed to the encapsulation of hydrated Eu3+ clusters by B15C5 and B18C6. On the contrary, the main fragment ions subsequent to the UV excitation of these complexes are B15C5+ and B18C6+ radical ions; the charge transfer occurs from H2O+ to B15C5 and B18C6 after the UV excitation. The position of the band origin for the H2O+·B18C6 complex (36323 cm–1) is almost the same as that for Rb+·B18C6 (36315 cm–1); the strength of the intermolecular interaction of H2O+ with B18C6 is similar to that of Rb+. The spectral features of the H2O+·B15C5 complex also resemble those of the Rb+·B15C5 ion. We measure IR–UV spectra of these complexes in the CH and OH stretching region. Four conformers are found for the H2O+·B15C5 complex, but there is one dominant form for the H2O+·B18C6 ion. This study demonstrates the production of radical ions by charge transfer from multivalent metal ions, their encapsulation by host molecules, and separate detection of their conformers by cold UV spectroscopy in the gas phase.

American Chemical Society2015