Sodium electron affinity

S = Heat of sublimation of sodium D = Dissociation energy of chlorine / = Ionization energy of sodium = Electron affinity of chlorine Uq = Lattice energy of sodium chloride AHf = Heat of formation of sodium chloride. 

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... 

Even the chemically robust perfluoroalkanes can undergo electron-transfer reactions (equation 4) because of their relatively high electron affinities [89]. Strong reduemg agents like alkali metals [90] or sodium naphthahde [91] are normally required for reaction, but perfluoroalkanes with low-energy, tert-C-F a anti-... 

Which element of each of the following pairs has the higher electron affinity (a) oxygen or fluorine (b) nitrogen or carbon (c) chlorine or bromine (d) lithium or sodium ... 

Using the appropriate data for the formation of sodium chloride, U (kj mol-1) = 109 + 121 + 496 — 349 — ( — 411) = 786 kj mol-1. Although this is a useful approach for determining the lattice energy of a crystal, the electron affinity of the atom gaining the electron is difficult to measure experimentally. 

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

The Effects of Complexing Agents. Cai et al.66 replaced the sodium counterion of MX-DNA with various aliphatic amine cations, e.g. spermine cation, and alkyltrimethylammonium cation as well as polymeric amine cations, such as poly-L-lysine and polyethylenimine to vary the separation between DNA duplexes. The radiation-produced electrons from the complexing agents readily transfer to the more electron affinic DNA. 

Electron transfer from polycyclic aromatic radical anions in polar solvents can also initiate propagation.120 168 169173 One of the early and best understood systems is naphthalene-sodium, a green solution of stable, solvated naphthalene radical anion.176 177 The electron transfer from the radical anion to the monomer yields a new radical anion [Eq. (13.33)]. The dominant reaction of the latter is its head-to-head dimerization to the stabile dimeric dicarbanion [Eq. (13.34)], which is the driving force for the electron transfer even when electron affinity of the monomer is less than that of the polycyclic molecule. Propagation proceeds at both ends of the chain ... 

The enthalpy of formation of sodium fluoride is —571 kj mol. Estimate the electron affinity of fluorine Compare your value with that giver in Table 23. 

Electron Affinity. In the formation of sodium chloride one of the steps involves the attachment of an electron to a gaseous chlorine atom, producing a chloride ion. 

The Principle of Hard and Soft Acids and Bases states that hard acids form more stable complexes with hard bases and soft bases form more stable complexes with soft acids. In orbital terms hard molecules have a large gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and soft molecules have a small HOMO-LUMO gap. In recent years it has been possible to correlate the hardness with the electronic properties of the atoms involved. Thus, if the enthalpy of ionisation (I) and the electron affinity (A) are known the so-called absolute hardness (t ) and absolute electronegativity (%) can be found from r = (I - A) / 2 and % = (I + A) / 2. For example, the first and second ionisation enthalpies of sodium are 5.14 and 47.29 eV. Thus for Na+, I = + 47.29 and A = + 5.14, so r = (47.29 - 5.14) / 2 = 21.1. Similarly for silver the first and second ionisation enthalpies are 7.58 and 21.49eV, so for Ag+ we have, n = (21.49 - 7.58) 12 = 6.9. 

The primary advantage of laser desorption is that abundant molecular or pseudomolecular ions are produced for many different classes of compounds. Positive pseudomolecular ions are most often formed by attachment of a cation, typically a proton, potassium, or sodium ion, to the parent molecule. Negative pseudomolecular ions can also be formed by laser desorption, usually by loss of a proton, or by electron attachment to molecules with a positive electron affinity. Often little fragmentation occurs (making this... 

Small quantities of excess oxygen had the effect of increasing the degree of ionization of sodium, whereas no such effect was observed when adding comparable quantities of N2 to the flame. We ascribe this difference to the different electron affinities, which are 0.44 eV for 02 and -1.5 eV for N2. 

Sample Why is it that sodium has a negative electron affinity while magnesium has a positive value ... 

The electron affinities of elements (Chap, 7) that form negative ions may be calculated by considering the formations of compounds containing such negative ions. The formation of such a compound from the elements (the heat of such a reaction being directly measurable) may be broken down into a series of simpler steps. The treatment is again called a Born-Haber cycle and is analogous to the treatment of the conversion of an alkali metal to its hydrated ion (discussed in Chap. 6). Consider the formation of sodium chloride from the elements ... 

As seen from the diagram, the heat of sublimation of sodium metal is S, the ionization potential of sodium is 7, the heat of dissociation of CU is Z>, the electron affinity of Cl is EA and the lattice energy (crystal energy) is designated by Exattice. The heat given off in the entire reaction, (often designated as Q) would be ... 

If we combine the ionization energy of sodium with the electron affinity of chlorine, we deduce that an overall energy input is required for the reaction... 

The transition from the atom to the cluster to the bulk metal can best be understood in the alkali metals. For example, the ionization potential (IP) (and also the electron affinity (EA)) of sodium clusters Na must approach the metallic sodium work function in the limit N - . We previously displayed this (1) by showing these values from the beautiful experiments by Schumacher et al. (36, 37) (also described in this volume 38)) plotted versus N". The electron affinity values also shown are from (39), (40) and (34) for N = 1,2 and 3, respectively. A better plot still is versus the radius R of the N-mer, equivalent to a plot versus as shown in Figure 1. The slopes of the lines labelled "metal sphere" are slightly uncertain those shown are 4/3 times the slope of Wood ( j ) and assume a simple cubic lattice relation of R and N. It is clear that reasonably accurate interpolation between the bulk work function and the IP and EA values for small clusters is now possible. There are, of course, important quantum and statistical effects for small N, e.g. the trimer has an anomalously low IP and high EA, which can be readily understood in terms of molecular orbital theory (, ). The positive trimer ions may in fact be "ionization sinks" in alkali vapor discharges a possible explanation for the "violet bands" seen in sodium vapor (20) is the radiative recombination of Na. Csj may be the hypothetical negative ion corresponding to EA == 1.2 eV... 

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