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Electron affinity can be defined in two equivalent ways. First, as the energy that is released by adding an electron to an isolated gaseous atom. The second (reverse) definition is that electron affinity is the energy required to remove an electron from a singly charged gaseous negative ion.
The electron affinity of molecules is a complicated function of their electronic structure. For instance the electron affinity for benzene is negative, as is that of naphthalene, while those of anthracene, phenanthrene and pyrene are positive. In silico experiments show that the electron affinity of hexacyanobenzene surpasses that of fullerene. [5]
According to this scale, fluorine is the most electronegative element, while cesium is the least electronegative element. [ 17 ] Trend-wise, as one moves from left to right across a period in the modern periodic table , the electronegativity increases as the nuclear charge increases and the atomic size decreases.
It is to be expected that the electronegativity of an element will vary with its chemical environment, [7] but it is usually considered to be a transferable property, that is to say that similar values will be valid in a variety of situations. Caesium is the least electronegative element (0.79); fluorine is the most (3.98).
Chemically, the nonmetals mostly have higher ionisation energies, higher electron affinities (nitrogen and the noble gases have negative electron affinities) and higher electronegativity values [n 1] than metals noting that, in general, the higher an element's ionisation energy, electron affinity, and electronegativity, the more nonmetallic ...
Many of the highly radioactive elements have values that must be predictions or extrapolations, but are unfortunately not marked as such. This is especially problematic for francium, which by relativistic calculations can be shown to be less electronegative than caesium, but for which the only value (0.7) in the literature predates these ...
Configurations of elements 109 and above are not available. Predictions from reliable sources have been used for these elements. Grayed out electron numbers indicate subshells filled to their maximum. Bracketed noble gas symbols on the left represent inner configurations that are the same in each period. Written out, these are: He, 2, helium : 1s 2
See also: Electronegativities of the elements (data page) There are no reliable sources for Pm, Eu and Yb other than the range of 1.1–1.2; see Pauling, Linus (1960). The Nature of the Chemical Bond. 3rd ed., Cornell University Press, p. 93.