To understand the concept of electron affinity as a measure of the energy required to add an electron to an atom or ion. To acknowledge the inverse partnership of ionization energies and electron affinities

The electron affinity ((EA)) of an aspect (E) is characterized as the energy change that occurs when an electron is added to a gaseous atom or ion:

< E_(g)+e^- ightarrow E^-_(g) ;;;   extenergy change=EA label7.5.1>

Unlike ionization energies, i beg your pardon are always positive because that a neutral atom because energy is compelled to remove an electron, electron affinities deserve to be an unfavorable (energy is released as soon as an electron is added), hopeful (energy need to be included to the device to produce an anion), or zero (the procedure is energetically neutral). This sign convention is continual with a an adverse value synchronized to the energy adjust for an exothermic process, i m sorry is one in which warm is exit (Figure (PageIndex1)).

You are watching: Which element has the highest most negative electron affinity

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Figure (PageIndex1): A Plot of routine Variation that Electron Affinity with Atomic Number for the an initial Six Rows the the periodic Table. An alert that electron affinities deserve to be both negative and positive. Indigenous Robert J. Lancashire (University of the West Indies).

The chlorine atom has actually the most an unfavorable electron affinity of any element, which means that an ext energy is released when an electron is added to a gas chlorine atom than to one atom of any other element:

< ce Cl(g) + e^- ightarrow Cl^- (g) ;;;  EA=-346; kJ/mol label7.5.2>

In contrast, beryllium walk not kind a stable anion, for this reason its reliable electron affinity is

< ce Be(g) + e^- ightarrow Be^- (g) ;;;  EA ge 0 label7.5.3>

Nitrogen is unique in that it has an electron affinity of about zero. Including an electron no releases nor needs a far-ranging amount of energy:

< ce N(g) + e^- ightarrow N^- (g) ;;;  EA approx 0 label7.5.4>

Generally, electron six become more negative across a heat of the periodic table.

In general, electron six of the main-group facets become less an adverse as we proceed down a column. This is due to the fact that as n increases, the extra electrons go into orbitals that are increasingly far from the nucleus.

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Figure (PageIndex2): Electron six (in kJ/mol) of the s-, p-, and d-Block Elements.

Atoms through the largest radii, which have the lowest ionization energies (affinity because that their very own valence electrons), additionally have the shortest affinity for an included electron. Over there are, however, two major exceptions to this trend:

The electron affinities of aspects B with F in the second row that the periodic table are less an unfavorable than those of the elements immediately listed below them in the third row. Apparently, the boosted electron–electron repulsions knowledgeable by electron confined to the reasonably small 2p orbitals conquer the enhanced electron–nucleus attraction at brief nuclear distances. Fluorine, therefore, has actually a reduced affinity because that an added electron than does chlorine. Consequently, the elements of the third heat (n = 3) have actually the most negative electron affinities. Farther under a column, the attraction because that an added electron decreases since the electron is entering an orbital an ext distant indigenous the nucleus. Electron–electron repulsions additionally decrease because the valence electrons accounting a higher volume the space. These effects tend come cancel one another, for this reason the alters in electron affinity within a family are lot smaller than the transforms in ionization energy. The electron six of the alkaline earth metals become more negative from be to Ba. The energy separation in between the to fill ns2 and also the north np subshells to reduce with enhancing n, so that formation of an anion native the heavier facets becomes energetically an ext favorable.What Is The Theme Of Tom Sawyer Themes, The Adventures Of Tom Sawyer Themes

Solution:

A We recognize that electron affinities end up being less an adverse going under a column (except for the anomalously low electron affinities of the elements of the second row), therefore we can predict that the electron affinity of Se is much more negative than that the Te. We also know that electron affinities become much more negative from left to right throughout a row, and also that the team 15 aspects tend to have actually values that space less an adverse than expected. Because Sb is located to the left that Te and also belongs to team 15, we predict the the electron affinity that Te is much more negative than that the Sb. The all at once order is Se practice (PageIndex1): difference Electron affinities of Rb, Sr, and also Xe

Based on your positions in the regular table, i m sorry of Rb, Sr, or Xe would certainly you predict to many likely kind a gaseous anion?

Answer

Rb


Summary

The electron affinity (EA) of an element is the energy readjust that occurs when an electron is included to a gaseous atom to provide an anion. In general, aspects with the most an unfavorable electron affinities (the highest possible affinity because that an added electron) are those with the the smallest size and highest ionization energies and also are situated in the upper right corner of the periodic table.


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