Atom affinity chlorine

The enthalpy of atomization of copper does not differ at all for the two compounds, and the atomization of chlorine adds only a small difference for the second mole of chlorine. The major energy cost for CuCl2 is the second ionization energy of copper which is compensated by the electron affinity to form the second chloride ion and especially the lattice energy. Since the electron ionized to form Cu2 is a d electron and does not break a noble gas structure, IE2 is not excessive, and both CuCl and CuCl2 are stable compounds. 

Which atom has the greatest electron affinity chlorine, bromine, iodine ... 

For most elements, the first electron gained is exothermic (energy given off). Chlorine s electron affinity (E.A.) is —349 kJ per mole of electrons gained. The higher the first electron affinity (chlorine s is high), the more likely the element is to form an anion. The electron affinities of the elements display loose trends to increase in a period with the atomic number. 

Look now at the relationship between these measurements and some others that bear upon them. For example, measurements of the ionization energy of sodium show that 51 eV of energy is required to remove to an infinite distance one electron from an isolated atom of sodium. Measurements of the electron affinity of chlorine show that 3-7 eV of energy is returned when one electron is returned from an infinite distance to an isolated atom of chlorine. At first glance, passing one electron from a sodium atom to a chlorine atom may seem unfavourable, to the extent of 1 -4 eV per molecule of sodium chloride. 

Blister agents that generally contain halogen atoms (usually chlorine atoms), such as mustard gas (HD), have a low proton affinity and therefore do not form stable positive ions at ambient pressnre. However, these chemicals (termed H agents in military codes but called B in this section) can form adduct ions, that is, B 02 (H20) i in the negative polarity as shown in Equation 13.3 ... 

Frankland and Crum Brown (1866) represented a double bond by two short lines (C, Fig. 45). In a Royal Institution lecture Crum Brown represented the union of calcium oxide and water by the equation D, Fig. 45, the two residues remaining united on account of the double relatedness of the calcium atom. He distinguished between valency and affinity chlorine is said to be saturated by. .. sodium or. .. silver, although the intimacy or firmness of the combination is not the same in the two cases. Crum Brown s view that the formulae did not indicate the physical, but merely the chemical position of the atoms was approved by Frankland, whereas Naquet used the crude idea of atoms provided with hooks which link them together, and some of Kekule s later formulae also suggest this (see Fig. 47, p. 555). 

This compound, which contains atoms arranged tetrahedrally around the boron atom, can readily be isolated from a mixture of dimethyl ether and boron trichloride. On occasions a chlorine atom, in spite of its high election affinity, will donate an electron pair, an example being found in the dimerisation of gaseous monomeric aluminium chloride to give the more stable Al2Clg in which each aluminium has a tetrahedral configuration ... 

Electron affinity and hydration energy decrease with increasing atomic number of the halogen and in spite of the slight fall in bond dissociation enthalpy from chlorine to iodine the enthalpy changes in the reactions... 

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... 

Chloroformates are versatile, synthetic intermediates, based on the affinity of the chlorine atoms for active hydrogen atoms. Chloroformates should be considered as intermediates for syntheses of pesticides, perfumes, dmgs, polymers, dyes, and other chemicals. Some of these products, eg, carbonates, are used as solvents, plastici2ers, or as intermediates for further synthesis. A significant use of chloroformates is for conversion to peroxydicarbonates, which serve as free-radical initiators for the polymeri2ation of vinyl chloride, ethylene, and other unsaturated monomers. The most widely used percarbonate initiators are diisopropyl peroxydicarbonate (IPP), di-2-ethyIhexylperoxydicarbonate (2-EHP), and di-j -butylperoxydicarbonate (SBP). The following Hst includes most of the commercially used percarbonates. 

Because the electron has a lower energy when it occupies one of the atom s orbitals, the difference E(C1) — E(Cl-) is positive and the electron affinity of chlorine is positive. Like ionization energies, electron affinities are reported either in electronvolts for a single atom or in joules per mole of atoms. 

The electron affinity of chlorine atoms is +349 kj-mol 1 (see Fig. 1.54), and so we know that 349 k )-mol 1 of energy is released when electrons attach to chlorine atoms to form anions ... 

The electron affinity of chlorine is negative, which means that energy is released when a chlorine atom gains an electron Cl(g) + e -> Cl (g) A E=E A = -348.5 kJ/mol... 

Finally, derivatives of the endogenous compound 2-octyl- y-bromoacetate (65) have been reported as FAAH inhibitors [79]. In a limited SAR study, it was found that replacement of the bromine with a chlorine atom had little effect on affinity. The replacement of the alkyl chain with oleyl-chain mimics resulted in an increase of affinity for FAAH (approximately 5-fold). The removal of the halogen and replacement with either a proton or methyl resulted in inactive compounds. The most potent compound identified in this series was compound (66) with an IC50 value of 0.6/rM [79]. 

Figure 5.16. Plot of data for the external heavy-atom quenching of pyrene fluorescence in benzene at 20°C. Polaro-graphic half-wave reduction potentials Ein are used as a measure of the electron affinity of the quencher containing chlorine (O), bromine ( ), or iodine (3). From Thomaz and Stevens<148) with permission of W. A. Benjamin, New York.

Figure A.l 1 shows the change in density of states due to chemisorption of Cl and Li. Note that the zero of energy has been chosen at the vacuum level and that all levels below the Fermi level are filled. For lithium, we are looking at the broadened 2s level with an ionization potential in the free atom of 5.4 eV. The density functional calculation tells us that chemisorption has shifted this level above the Fermi level so that it is largely empty. Thus, lithium atoms on jellium are present as Li, with 8 almost equal to 1. Chemisorption of chlorine involves the initially unoccupied 3p level, which has the high electron affinity of 3.8 eV. This level has shifted down in energy upon adsorption and ended up below the Fermi level, where it has become occupied. Hence the charge on the chlorine atom is about-1.

---