The electron affinity trend describes the trend across the regular table and describes exactly how much energy in one atom is released or spent when an electron is included to a neutral atom or the energy adjust that occurs once an electron is included to a neutral atom.

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The electron affinity trend explains how as one complies with the routine table left to appropriate electron affinity increases and how it normally decreases as one moves down a group of elements, top to bottom. While it is a short description the the electron affinity trend, it would be advantageous to dig deeper into the relationship between electron affinity and the regular table.


A Refresher on Atoms

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Atoms room made the end of three various parts: protons, neutrons, and electrons. The protons and neutrons are discovered within the facility of the atom, the atom’s nucleus. The cell nucleus of the atom includes almost every one of the atom’s mass, and both the neutrons and protons that comprise the atom have basically the very same mass (though the massive of the proton is slightly less).

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The proton in the atom room positively charged, and also the number of protons uncovered within the nucleus basically defines what element an atom is. The variety of protons in ~ an atom is the element’s atomic number. The neutrons in ~ the atom have no charge, therefore their neutrality. The neutron are offered as a suggest of comparison to find the fixed of electrons and protons.

“We’re protons and also electrons/ residents in one nucleus.” — Afeefa

Electrons are about 1800 times smaller sized than one of two people neutrons or protons, and they have actually a an adverse charge. The electron orbit the nucleus of the atom, and they orbit in lot of layers known as shells. The outermost layer of the electron shells is well-known as the valence shell, and it’s typically the just layer the matters in chemistry. The electron in the valence shell are recognized as valence electrons, and they room the electron most capable of bonding with other atoms to develop chemicals bonds and molecules.


Elements the have finish valence shells, choose the noble gases, are stable and also chemically non-reactive. Facets that have only one electron in their valence shell, favor alkali metals, or are absent a single electron in the shell (like halogens) are the most reactive elements. Reactivity and electron affinity room tightly correlated, with the reactivity the an element increasing as the electron affinity increases. In other words, the higher an element’s tendency to get electrons, the more reactive the aspect is.

Electron Affinity

Ions of atoms may have actually a net hopeful charge or a net negative charge. Positive charged atom are dubbed cations while negative charged ion are referred to as anions. The energy of an atom has can be obtained or lost through chemistry reactions, so this chemical reactions type either anions or cations. Ionization energies attend to the formation of confident ions if electron affinities address the development of an unfavorable ions. It’s essential to mental that, so you’ll recognize that electron six deal specifically with an adverse ions that atoms and that their use is virtually always relegated to the facets found within teams 16 and also 17 of the facet table.

“The protons are positive and also the electron are negative and, the the two, i am sure that the electrons room nicer.” — Robert Benchley

The electron affinity of one atom depends upon as soon as it is added to the atom. The initial addition of one electron to a neutral atom, the very first electron affinity, will always have negative energy. This is since energy is released as soon as an electron is included to a neutral atom. The ion is currently negative, and much more energy is important when one electron is being added to a an adverse ion. This way that the power required overwhelms the energy released by the electron attachment process, and also so the second electron affinity will be positive.

The addition of one electron to a metal facet requires energy. This is because metals don’t exert a very strong pull on their valence electrons and are because of this lose electrons in the valence shell quite easily, coming to be cations. Because that this reason, numerous metals have really low electron affinities.


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Photo: Geralt via Pixabay

Electron affinities are given in kj/mol (joules per mole), a measurement of given power per lot of material. As an example of the reality that metals have low electron affinity, look at the adhering to electron affinity values for the metals found in team 1 that the regular table:

Lithium (Li) Electron Affinity: 60 KJ mol-1Sodium (Na) Electron Affinity: 53 KJ mol-1Rubidium (Rb) Electron Affinity: 47 KJ mol-1Cesium (Cs) Electron Affinity: 46 KJ mol-1

Unlike metals, when a nonmetal benefit an electron, the amount of energy adjust is frequently negative. This is due to the fact that nonmetals have enough energy to kind negatively charged ions, anions. This way that the electron affinity value of nonmetals is typically negative. Nonmetals have an ext electron affinity than metals do due to the fact that of your atomic structure. Nonmetals have much more valence electrons, which renders it less complicated for them to get electrons and also complete a set. The valence shell likewise tends to be closer come the nucleus 보다 in metals, meaning that that more difficult to remove electrons indigenous nonmetals and also easier for nonmetals to entice electrons come them. As an example of the greater electron affinity that nonmetals have, look at the electron affinity because that the halogens in group 17:

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

The Electron Affinity Trend

The Electron Affinity trend, like other trends in the routine table, reflects the reality that electron affinity complies with a predictable tendency as one reads the routine table. In this case, electron affinity boosts from peak to bottom and also left to right. Together one moves from the bottom that the routine table upwards through groups (columns) of elements, electron affinity tends to increase. Electron affinity additionally tends to boost as one complies with the periodic table native left come right throughout periods (rows) of the table.

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“Protons give an atom its identity, electron its personality.” bill Bryson

The better the distance between the nucleus and also the shells of the electrons, the less attraction over there is and also the less energy released when an electron is introduced to the outside shell. The an ext valence electron an facet has, the an ext likely that is to gain electrons so the a complete octet that electrons will certainly be formed. The opposite tendency holds true together well, electron affinity to reduce from best to left and also down the groups because the electrons are situated farther far from the nucleus and also therefore have actually less attraction. The factor that elements lower in teams don’t have greater electron affinities regardless of their greater number of valence electrons is the shielding effect. The shielding effect increases as one moves under a group, making electrons repel each various other more.


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