Electron affinity is characterized as the adjust in power (in kJ/mole) of a neutral atom (in the gas phase) when an electron is included to the atom to type a negative ion. In various other words, the neutral atom"s likelihood of getting an electron.

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Energy of an atom is defined when the atom loses or gains energy through sdrta.netistry reactions that reason the lose or gain of electrons. A sdrta.netistry reaction the releases energy is dubbed an exothermic reaction and also a sdrta.netistry reaction that absorbs power is called an endothermic reaction. Power from an exothermic reaction is negative, thus power is offered a negative sign; whereas, energy from one endothermic reaction is positive and energy is given a optimistic sign. An example that demonstrates both processes is once a person drops a book. When he or she lifts a book, he or she offers potential power to the publication (energy absorbed). However, when the that or she fall the book, the potential energy converts chin to kinetic energy and comes in the kind of sound once it access time the ground (energy released).

When one electron is added to a neutral atom (i.e., an initial electron affinity) energy is released; thus, the an initial electron affinities space negative. However, an ext energy is forced to add an electron to a negative ion (i.e., 2nd electron affinity) i m sorry overwhelms any the release of energy from the electron attachment procedure and hence, second electron affinities are positive.

very first Electron Affinity (negative energy because energy released):

< ceX (g) + e^- ightarrow X^- (g) label1>

2nd Electron Affinity (positive energy since energy needed is much more than gained):

< ceX^- (g) + e^- ightarrow X^2- (g) label2>

First Electron Affinity

Ionization energies are constantly concerned with the formation of optimistic ions. Electron affinities are the an unfavorable ion equivalent, and their use is almost always border to facets in groups 16 and also 17 of the routine Table. The first electron affinity is the power released as soon as 1 mole of gaseous atom each obtain an electron to type 1 mole of gas -1 ions. It is the power released (per mole that X) once this change happens. First electron six have negative values. For example, the very first electron affinity the chlorine is -349 kJ mol-1. Through convention, the an unfavorable sign shows a relax of energy.

When one electron is included to a metal element, power is necessary to get that electron (endothermic reaction). Metals have a much less likely chance to get electrons due to the fact that it is much easier to shed their valance electron and kind cations. It is easier to lose their valence electrons because metals" nuclei execute not have actually a strong pull on your valence electrons. Thus, metals are known to have actually lower electron affinities.

Example (PageIndex1): team 1 Electron Affinities

This tendency of reduced electron affinities for steels is described by the group 1 metals:

Lithium (Li): -60 KJ mol-1 sodium (Na): -53 KJ mol-1 Potassium (K): -48 KJ mol-1 Rubidium (Rb): -47 KJ mol-1 Cesium (Cs): -46 KJ mol-1

Notice the electron affinity decreases down the group.

When nonmetals gain electrons, the energy adjust is usually an unfavorable because they give off power to kind an anion (exothermic process); thus, the electron affinity will certainly be negative. Nonmetals have actually a better electron affinity than metals since of their atomic structures: first, nonmetals have an ext valence electron than steels do, hence it is less complicated for the nonmetals to get electrons to fulfill a steady octet and also secondly, the valence electron covering is closer come the nucleus, therefore it is more tough to eliminate an electron and it simpler to attract electrons from other elements (especially metals). Thus, nonmetals have a higher electron affinity than metals, meaning they are much more likely to gain electrons 보다 atoms v a lower electron affinity.

Example (PageIndex2): team 17 Electron Affinities

For example, nonmetals like the aspects in the halogens collection in team 17 have a greater electron affinity 보다 the metals. This trend is described as below. Notice the negative sign for the electron affinity which mirrors that energy is released.

Fluorine (F) -328 kJ mol-1 Chlorine (Cl) -349 kJ mol-1 Bromine (Br) -324 kJ mol-1 Iodine (I) -295 kJ mol-1

Notice that electron affinity decreases down the group, however increases up through the period.

As the surname suggests, electron affinity is the capacity of an atom to accept an electron. Unequal electronegativity, electron affinity is a quantitative measure up of the energy readjust that occurs once an electron is included to a neutral gas atom. The an ext negative the electron affinity value, the greater an atom"s affinity because that electrons.

api/deki/files/55500/ElectronAffinity.png?revision=1&size=bestfit&width=780&height=456" />Figure (PageIndex1): A Plot of routine Variation the Electron Affinity v Atomic Number for the an initial Six Rows of the periodic Table. An alert that electron affinities have the right to be both an adverse and positive. Native Robert J. Lancashire (University of the West Indies).

Why is Fluorine an Anomaly?

The incoming electron is going to be closer come the nucleus in fluorine than in any kind of other of this elements, so girlfriend would mean a high worth of electron affinity. However, due to the fact that fluorine is such a tiny atom, friend are putting the new electron right into a an ar of room already crowded v electrons and also there is a significant amount of repulsion. This repulsion lessens the attraction the just arrived electron feels and so lessens the electron affinity. A comparable reversal that the supposed trend happens between oxygen and also sulfur in group 16. The first electron affinity the oxygen (-142 kJ mol-1) is smaller than the of sulfur (-200 kJ mol-1) for exactly the same reason that fluorine"s is smaller than chlorine"s.

Comparing group 16 and also Group 17 values

As you could have noticed, the an initial electron affinity of oxygen ((-142; kJ; mol^-1)) is less than the of fluorine ((-328; kJ; mol^-1)). Likewise sulfur"s ((-200; kJ; mol^-1)) is less than chlorine"s ((-349; kJ; mol^-1)). Why? It"s merely that the team 16 element has 1 less proton in the nucleus than its following door neighborhood in group 17. The quantity of screening is the very same in both. That method that the net pull indigenous the cell core is much less in team 16 보다 in group 17, and so the electron affinities are less.

The reactivity of the elements in group 17 falls as friend go down the group - fluorine is the many reactive and iodine the least. Regularly in your reactions this elements kind their negative ions. The an initial impression the is sometimes provided that the fall in reactivity is because the incoming electron is organized less strongly as you go under the group and also so the negative ion is much less likely to form. The explanation look at reasonable until you incorporate fluorine!

An all at once reaction will certainly be comprised of lots of different steps every involving power changes, and also you can not safely try to explain a tendency in terms of just one of those steps. Fluorine is much much more reactive 보다 chlorine (despite the reduced electron affinity) due to the fact that the energy released in other steps in that reactions much more than makes up because that the reduced amount of power released as electron affinity.

Second Electron Affinity

You are only ever likely to fulfill this through respect come the group 16 elements oxygen and sulfur i m sorry both kind -2 ions. The 2nd electron affinity is the energy required to include an electron to each ion in 1 mole of gas 1- ion to create 1 mole of gaseous 2- ions. This is much more easily viewed in prize terms.

< X^- (g) + e^- ightarrow X^-2 (g) label3>

It is the energy needed to bring out this change per mole of (X^-).

Why is power needed to perform this? You space forcing one electron into an already an adverse ion. It"s no going to go in willingly!

< O_g + e^- ightarrow O^- (g) ;;; ext1st EA = -142 kJ mol^-1 label4>

< O^-_g + e^- ightarrow O^2- (g) ;;; ext2nd EA = +844 kJ mol^-1 label5>

The hopeful sign mirrors that you need to put in power to perform this change. The second electron affinity of oxygen is specifically high because the electron is being compelled into a small, very electron-dense space.

See more: How Many Moles Of Oxygen Are In 25.45 G Of Caco3, Https://Answers

Practice Problems

when an electron is added to a nonmetal atom, is energy released or absorbed? Why do nonmetal atoms have a greater electron affinity than steel atoms? Why space atoms with a short electron affinity more likely to lose electrons than get electrons? together you relocate down a team of the periodic table, walk electron affinity rise or decrease, if so, why? Why perform nonmetals desire to acquire electrons? Why execute metals have a low electron affinity?


energy is released as soon as a electron is added to a nonmetal. Nonmetals have actually a better electron affinity 보다 metals since their atomic structure allows them to get electrons fairly than shed them. Atoms with a low electron affinity want to give up their valence electrons due to the fact that they are further from the nucleus; together a result, they carry out not have a strong pull on the valence electrons. As you move down a group on the periodic table, electron affinity decreases. First, the electron are put in energy levels further away indigenous the nucleus, which results in electrons not having a solid attraction to the nucleus; secondly, the atom does no want obtain electrons due to the fact that there is minimal fee on the outer power levels from the nucleus; and also lastly, the shielding impact increases, bring about repulsion in between the electrons, for this reason they move further from every other and also the nucleus itself. Nonmetals desire to obtain electrons since they have an ext valence electrons than metals, so the is easier for them to get electrons than shed the valance electrons to satisfy a secure octet. In addition, nonmetals" valance electrons are closer come the nucleus, therefore allowing more attraction in between the two. Metals have a low electron affinity (a less likely possibility to gain electrons) since they want to provide up their valence electrons quite than obtain electrons, i m sorry require more energy 보다 necessary. In addition, they perform not have actually a strong pull top top the valance electrons due to the fact that they are much away indigenous the nucleus, hence they have less power for one attraction.