Electron endothermic

Noble gases have filled shells or subshells. Therefore, they have little tendency to accept electrons (endothermic). 

To date there is no evidence that sodium forms any chloride other than NaCl indeed the electronic theory of valency predicts that Na" and CU, with their noble gas configurations, are likely to be the most stable ionic species. However, since some noble gas atoms can lose electrons to form cations (p. 354) we cannot rely fully on this theory. We therefore need to examine the evidence provided by energetic data. Let us consider the formation of a number of possible ionic compounds and first, the formation of sodium dichloride , NaCl2. The energy diagram for the formation of this hypothetical compound follows the pattern of that for NaCl but an additional endothermic step is added for the second ionisation energy of sodium. The lattice energy is calculated on the assumption that the compound is ionic and that Na is comparable in size with Mg ". The data are summarised below (standard enthalpies in kJ) ... 

Pure hydrazine is a colourless liquid, melting point 275 K, and boiling point 387 K. It is surprisingly stable for an endothermic compound = -i- 50.6 kJ mol ). Each nitrogen atom has a lone pair of electrons and either one or both nitrogen atoms are able to accept protons to give and the less stable... 

Were we to simply add the ionization energy of sodium (496 kJ/mol) and the electron affin ity of chlorine (—349 kJ/mol) we would conclude that the overall process is endothermic with AH° = +147 kJ/mol The energy liberated by adding an electron to chlorine is msuf ficient to override the energy required to remove an electron from sodium This analysis however fails to consider the force of attraction between the oppositely charged ions Na" and Cl which exceeds 500 kJ/mol and is more than sufficient to make the overall process exothermic Attractive forces between oppositely charged particles are termed electrostatic, or coulombic, attractions and are what we mean by an ionic bond between two atoms... 

Bonding of Hydrogen to Other Atoms. The hydrogen atom can either lose the 1 valence electron when bonding to other atoms, to form the ion, or conversely, it can gain an electron in the valence shell to form the hydride ion, (see Hydrides). The formation of the ion is a very endothermic process ... 

A guide to tire stabilities of inter-metallic compounds can be obtained from the semi-empirical model of Miedema et al. (loc. cit.), in which the heat of interaction between two elements is determined by a contribution arising from the difference in work functions, A0, of tire elements, which leads to an exothermic contribution, and tire difference in the electron concentration at tire periphery of the atoms, A w, which leads to an endothermic contribution. The latter term is referred to in metal physics as the concentration of electrons at the periphery of the Wigner-Seitz cell which contains the nucleus and elecUonic structure of each metal atom within the atomic volume in the metallic state. This term is also closely related to tire bulk modulus of each element. The work function difference is very similar to the electronegativity difference. The equation which is used in tire Miedema treatment to... 

The shock-modified composite nickel-aluminide particles showed behavior in the DTA experiment qualitatively different from that of the mixed-powder system. The composite particles showed essentially the same behavior as the starting mixture. As shown in Fig. 8.5 no preinitiation event was observed, and temperatures for endothermic and exothermic events corresponded with the unshocked powder. The observations of a preinitiation event in the shock-modified mixed powders, the lack of such an event in the composite powders, and EDX (electron dispersive x-ray analysis) observations of substantial mixing of shock-modified powders as shown in Fig. 8.6 clearly show the first-order influence of mixing in shock-induced solid state chemistry. 

The ground-state electronic structure of As, as with all Group 15 elements features 3 unpaired electrons ns np there is a substantial electron affinity for the acquisition of 1 electron but further additions must be effected against considerable coulombic repulsion, and the formation of As is highly endothermic. Consistent with this there are no ionic compounds containing the arsenide ion and... 

Under the influence of thermal motion and on endothermic electron transition from the OH ion to the Me ion in alkali metal hydroxides the formation of the Me. and OH. radicals takes place. As a result, free va-... 

The decompositions of these compounds are of interest since they are used as binders in electron-emissive coatings [1023]. The initial stage of the endothermic reaction in vacuum or nitrogen (520—820 K) yields residual carbonate and a small quantity of carbon. Changes in surface area during reactions have been measured. The main volatile product is HCHO, but secondary, exothermic reactions occur on the surface of the product carbonate so that the overall reaction is... 

Reactions of D with D20 and of 0 with 02, N20, and N02 have been studied with a magnetic sector mass spectrometer. Competition between electron transfer and ion-atom interchange has been observed in the production of 02 by reaction of 0 with 02, an endothermic reaction. The negative ion of the reacting neutral molecule is formed in 02, N2Of and N02 but not in D20. Rate constants have been estimated as a function of repeller potential. 

The initial kinetic energy of 0 ions produced by dissociative attachment in 02 at an electron energy of 6.9 e.v. may be determined from Equation 4 to be 1.64 e.v. using values of 1.465 e.v. (1) for A(0) and 5.09 e.v. (7) for D(O—O). The residence time for 0 ions calculated from Equation 1 is 6.0 X 10 7 sec. at 10 volts repeller potential. Rate constants for Reaction 6 determined from data at varying Vr are shown in Table I and are seen to increase sharply with increasing repeller potential, as expected for an endothermic process. 

The most interesting results of the computational data, however, concern the addition of the second electron which is strongly endothermic in all cases. In other words, these dianions are predicted to dissociate an electron in the gas phase spontaneously. In solution or the solid state, it is possible that the ions could be stabilized by the effects of counter cations. This stabilization has been accomplished for the boron dianions which crystallized as contact ion pairs [47-50]. However, as indicated above, no success has been achieved so far in... 

The basic information is the fact that formation of PC/Cu alloys is rather exothermic (15) so that one would expect more pronounced changes in the electronic structure of Pt and Cu, than with, e.g. Pt/Au, Pt/Ag, (endothermic alloy formation) or Pt/Re, Pd/Ag, Pd/Au (moderately exothermic). 

The mechanism involves a metal atom insertion into the O—H bond, thus resulting in the formation of an adsorbed metal—OH species (at the same or similar binding site) and a new metal—H bond. This is a classic bond activation process, which involves a significant stretch of the O—H bond in order to lower the antibonding ooh orbital to enable it to accept electron density from the metal. The reaction has been calculated by DFT to be endothermic by +90 kJ/mol over Pt(lll) surfaces with an activation barrier of +130 kJ/mol [Desai et al., 2003b]. 

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