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

The electron affinity ($$EA$$) of an element $$E$$ is defined as the energy change that occurs as soon as an electron is added to a gaseous atom or ion:

\< E_(g)+e^- \rightarrow E^-_(g) \;\;\;  \textenergy change=EA \label7.5.1\>

Unlike ionization energies, i beg your pardon are always positive for a neutral atom because energy is forced to remove an electron, electron affinities can be negative (energy is released when an electron is added), positive (energy need to be added to the system to create an anion), or zero (the process is energetically neutral). This authorize convention is constant with a negative value coincided to the energy adjust for an exothermic process, i m sorry is one in which heat is released (Figure $$\PageIndex1$$).

You are watching: Do noble gases have electron affinity Figure $$\PageIndex1$$: A Plot of routine Variation that Electron Affinity through Atomic Number because that the first Six Rows that the regular Table. An alert that electron affinities have the right to be both an adverse and positive. From Robert J. Lancashire (University of the West Indies).

The chlorine atom has the most an adverse electron affinity of any kind of element, which method that much more energy is released when an electron is added to a gas chlorine atom than to an atom of any kind of other element:

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

In contrast, beryllium does not form a secure anion, for this reason its efficient electron affinity is

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

Nitrogen is distinct in the it has an electron affinity of roughly zero. Adding an electron neither releases nor calls for a significant amount of energy:

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

Generally, electron six become more negative throughout a row of the routine table.

In general, electron affinities of the main-group facets become less negative as we proceed down a column. This is due to the fact that as n increases, the extra electrons go into orbitals that room increasingly far from the nucleus. Figure $$\PageIndex2$$: Electron affinities (in kJ/mol) of the s-, p-, and also d-Block Elements.

Atoms v the largest radii, which have actually the shortest ionization energies (affinity because that their very own valence electrons), likewise have the shortest affinity because that an added electron. There are, however, two major exceptions to this trend:

The electron six of elements B with F in the 2nd row that the routine table room less an unfavorable than those of the elements immediately listed below them in the 3rd row. Apparently, the enhanced electron–electron repulsions competent by electron confined to the reasonably small 2p orbitals conquer the enhanced electron–nucleus attraction at quick nuclear distances. Fluorine, therefore, has a reduced affinity for an added electron than does chlorine. Consequently, the aspects of the third row (n = 3) have the most an adverse electron affinities. Farther down a column, the attraction for an added electron decreases because the electron is entering an orbital more distant indigenous the nucleus. Electron–electron repulsions likewise decrease because the valence electrons occupy a greater volume of space. These effects tend to cancel one another, so the transforms in electron affinity within a household are lot smaller 보다 the alters in ionization energy. The electron affinities 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 north np subshells reduce with enhancing n, for this reason that formation of an anion from the heavier facets becomes energetically an ext favorable.[Image_Link]https://ptcouncil.net/

Example $$\PageIndex1$$: difference Electron six of Sb, Se, and Te

Based on your positions in the regular table, i m sorry of Sb, Se, or Te would you guess to have the most an unfavorable electron affinity?

Given: three elements

Asked for: element with most an unfavorable electron affinity

Strategy:

find the elements in the periodic table. Usage the patterns in electron six going down a shaft for elements in the exact same group. Similarly, usage the patterns in electron affinities from left to best for elements in the very same row. Ar the aspects in order, listing the facet with the most an adverse electron affinity first.

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Solution:

A We know that electron affinities become less an unfavorable going down a obelisk (except for the anomalously short electron affinities of the facets of the 2nd row), therefore we have the right to predict the the electron affinity the Se is an ext negative than that the Te. We additionally know that electron six become an ext negative indigenous left come right throughout a row, and also that the team 15 elements tend to have actually values that are less an unfavorable than expected. Since Sb is situated to the left of Te and belongs to team 15, we predict the the electron affinity the Te is much more negative 보다 that the Sb. The all at once order is Se exercise $$\PageIndex1$$: contrasting Electron affinities of Rb, Sr, and Xe

Based on your positions in the periodic table, i m sorry of Rb, Sr, or Xe would certainly you guess to most likely form a gas anion?