Electron Affinity

The energy is released while forming an anion from a neutral atom. When one electron moves to a neutral gaseous atom to generate a negative ion, the electron affinity changes. So, negative electron affinity favours electron addition. Not all elements generate stable negative ions, therefore electron affinity is zero or positive.

What is Electron Affinity?

The energy released when an electron is added to a neutral atom to produce a negatively charged ion is called electron affinity. Only a few chemical elements, mostly halogens, have measured electron affinities. An element’s electron affinity measures its inclination to behave as an oxidising agent (an electron acceptor) and is relevant to the chemical bonds it forms with other elements.

Periodic Trends

The affinities of electrons are famously difficult to determine. Electron affinity is inversely proportional to atomic size. The enhanced nuclear attraction causes an increase in electron affinity from left to right over a period.

Electron affinities should decrease as one moves along the group, as electrons are added further from the nucleus. It becomes easier to release the electron since it is no longer securely bonded

The electron gain enthalpy rises as we proceed from left to right in a period owing to the reduction in atomic size due to the increases in the nuclear force. As a result, electron gain enthalpy decreases as the atomic size rises while travelling down a group in the periodic table.

Because it is always negative, the initial electron affinities are always exothermic. There will be a positive or endothermic electron affinity for the second element. As a result, a second electron must be compelled into the mono negative ion for this to occur successfully. The Born-Haber cycle provides information on electron affinity that cannot be acquired directly.

Factors affecting Electron Affinity

Nuclear Charge, Atomic Size, and Electronic Configuration effect electron affinity. More nuclear charge means more electron attraction. Thereby, Increasing electron affinity. The nuclear charge is the nucleus’s attraction to electrons. The stronger the nucleus’ attraction, the more electrons will connect to the atom. The bigger an atom, the further the nucleus is from the electron. This reduces electron attraction. Thus, Electron affinity is low.

Electronic affinity grows along with the group and declines over the eras. A stable atomic configuration means less electron uptake. Its electron affinity will be lower. Stable electronic configuration components have essentially little electron affinity. The tiny inclination to accept another electron causes this. Inert gases lack electron affinities. Beryllium and calcium have little electron affinity. Full or half-filled orbits reduce electron affinity. Be and N have low electron affinity because their valence shells are full. Symmetry stabilizes filled orbits. These elements will accept the fewest electrons. Electron affinity often follows this trend: Group 1 and 13 metals > Group 2 metals > Halogens

Electron Affinity of Halogens

Ionization potential is the energy needed to eliminate a gaseous electron. Adding an electron releases energy, thus removing one releases energy. Electron affinity is the energy produced when a gaseous neutral atom absorbs an electron and becomes a negatively charged ion. When the initial electron is added to an atom, a monovalent anion is released, releasing energy. Adding another electron to this anion repels it, absorbing energy. Further electron affinities are positive.

First Electron Affinity

First, 1 mole of gaseous atoms gaining an electron to become 1 mole of gaseous -1 ions releases energy. This change releases (per mole of X) energy. Negative electron affinities first. Chlorine’s electron affinity is -349 kJ mol-1. Negative signs indicate energy release.

Adding an electron to metal requires energy (endothermic reaction). Metals lose their valance electrons and produce cations more easily than they receive electrons. Metals’ nuclei don’t strongly tug on their valence electrons, therefore losing them is easy. Also, metals’ electron affinities are lower.

Non-Metals Vs Metals

The nonmetals are found to the right of the line, the metalloids are the elements that are directly close to the line, and the metals are put to the left of the line (except hydrogen, which is a nonmetal).

Metals: Metals prefer to give up their valence electrons to create cations since this allows them to maintain a completely stable octet. They achieve this by consuming energy, which is known as being endothermic. In comparison to that of nonmetals, the electron affinity of metals is much lower.

Non-metals: To achieve a completely stable octet, nonmetals strive to accumulate electrons so that they may give rise to anions. They give up energy in the form of an exothermic reaction to acquire electrons to form an anion; hence, the electron affinity of nonmetals is greater than that of metals.

Patterns in Electron Affinity

Electron affinity advances upward for groups and from left to right through periods on a periodic table when electrons are added to energy levels, drawing them closer to the nucleus. Greater distance means less attraction, therefore adding an electron to the outer orbital releases less energy. More valence electrons mean a greater chance of forming a stable octet. Fewer valence electrons mean fewer electron gains. Electron affinity drops down the groups and from right to left over the periods because electrons are positioned at a higher energy level distant from the nucleus, reducing its pull.

FAQs on Electron Affinity

Q.1 Why is Fluorine an anomaly?

Answer: Due to fluorine’s tiny size, strong electronegativity, low dissociation enthalpy of F-F bonds, and lack of d-orbitals in the valence shell, it exhibits unusual behaviour. Fluorine’s reactions are almost exclusively exothermic (due to the short and strong bond formed by it with other elements).

Q.2 Explain Second Electron Affinity?

Answer: Adding one electron to each ion in a mole of gaseous 1-ions to make a mole of gaseous 2-ions is the second electron affinity. Per mole of X-, the amount of energy required to perform this transformation. You’re introducing an extra negative ion to an already-negative atom by introducing an electron.