Selection, Assignment, and Correlations of Atomic Electron Affinities

Selection, Assignment, and Correlations of Atomic Electron Affinities 

The electron affinities Ea of the main group atoms are the most precisely measured values. Recall that the Ea is the difference in energy between the most stable state of the neutral and a specific state of a negative ion. It was once believed that only one bound anion state of atoms and molecules could exist. However, multiple bound states for atomic and molecular anions have been observed. This makes it necessary to assign the experimental values to the proper state. The random uncertainties of some atomic Ea determined from photodetachment thresholds occur in parts per million. These are confirmed by photoelectron spectroscopy, surface ionization, ion pair formation, and the Born Haber cycle. Atomic electron affinities illustrate the procedure for evaluating experimental Ea. 

Random and systematic errors are characteristics of the method, not the values. Random errors can be determined by repeating the experiment. Systematic errors can only be determined by comparisons of values determined by different methods. Uncertainties can be estimated from precision and accuracy plots if it is assumed that there are only random errors. The Ea of the d and f block elements, electronegativities, and work functions of the elements will be evaluated in this chapter using this procedure. 

The extrapolation of values in the Periodic Table for the main group of elements can be examined and applied to the transition elements. The evaluated values can be combined with ionization potentials to obtain Mulliken electronegativities. These may be correlated with other electronegativities and the work functions of the elements. This provides another example of the use of the Periodic Table to evaluate and predict values. 

The Electron Capture Detector and the Study of Reactions with Thermal Electrons 

---

SELECTION, ASSIGNMENT, AND CORRELATIONS OF ATOMIC ELECTRON AFFINITIES... 

---