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

The electron affinity ((EA)) of an element (E) is identified as the energy change that occurs when an electron is included 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 constantly positive for a neutral atom since energy is required to eliminate an electron, electron affinities deserve to be an unfavorable (energy is released as soon as an electron is added), hopeful (energy should be added to the mechanism to develop an anion), or zero (the procedure is energetically neutral). This authorize convention is consistent with a an unfavorable value synchronized to the energy adjust for one exothermic process, which is one in which warm is released (Figure (PageIndex1)).

You are watching: Select the element with the most negative electron affinity

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Figure (PageIndex1): A Plot of routine Variation the Electron Affinity with Atomic Number because that the first Six Rows that the routine Table. An alert that electron affinities have the right to be both an unfavorable and positive. Indigenous Robert J. Lancashire (University that the West Indies).

The chlorine atom has the most an unfavorable electron affinity of any kind of element, which way that more energy is released as soon as an electron is added to a gaseous chlorine atom than to one atom of any type of other element:

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

In contrast, beryllium does not type a steady anion, so 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 actually an electron affinity of roughly zero. Including an electron neither releases nor calls for a significant amount that energy:

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

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

In general, electron six of the main-group facets become less an unfavorable as we continue down a column. This is due to the fact that as n increases, the extra electrons get in orbitals that room increasingly far from the nucleus.

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

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

The electron six of facets B with F in the 2nd row of the routine table room less an adverse than those that the aspects immediately listed below them in the third row. Apparently, the raised electron–electron repulsions proficient by electrons confined come the relatively small 2p orbitals get rid of the enhanced electron–nucleus attraction at quick nuclear distances. Fluorine, therefore, has a lower affinity because that an added electron than does chlorine. Consequently, the facets of the third heat (n = 3) have the most an unfavorable electron affinities. Farther under a column, the attraction because that an included electron decreases due to the fact that the electron is start an orbital more distant native the nucleus. Electron–electron repulsions additionally decrease since the valence electrons occupy a greater volume of space. These effects tend come cancel one another, for this reason the transforms in electron affinity within a family members are lot smaller 보다 the transforms in ionization energy. The electron six of the alkaline planet metals become much more negative from it is in to Ba. The energy separation in between the fill ns2 and also the empty np subshells reduce with raising n, so that development of one anion indigenous the heavier elements becomes energetically an ext favorable.Chrome Vanadium Steel Vs Carbon Steel Vs Carbon Steel, Chrome Vanadium Steel

Solution:

A We recognize that electron affinities end up being less an unfavorable going down a column (except because that the anomalously low electron affinities of the elements of the 2nd row), so we deserve to predict the the electron affinity the Se is an ext negative 보다 that of Te. We also know that electron affinities become an ext negative indigenous left come right throughout a row, and that the group 15 aspects tend to have values that space less negative than expected. Due to the fact that Sb is located to the left the Te and also belongs to group 15, we predict the the electron affinity of Te is much more negative 보다 that of Sb. The in its entirety order is Se exercise (PageIndex1): difference Electron six of Rb, Sr, and also Xe

Based on your positions in the periodic table, which of Rb, Sr, or Xe would you predict to many likely kind a gas anion?

Answer

Rb


Summary

The electron affinity (EA) the an aspect is the energy change that occurs as soon as an electron is added to a gas atom to give an anion. In general, facets with the most an adverse electron affinities (the greatest affinity for an included electron) are those v the smallest size and also highest ionization energies and also are situated in the upper right corner of the periodic table.


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