These repulsion forces are generated by inner electrons positioned between the nuclei and the outer electrons.Īs we travel down each group, the influence of the shielding effect increases. This rule acknowledges that while nuclei attract valence electrons, repulsion forces counter this attraction. We can rationalize this by considering the shielding effect. The number of valence electrons increase as we move down groups in the periodic table, as electron affinity decreases. Let’s consider how valence electrons impact electron affinity trends. As discussed, electron affinities increase from left to right across periods electron affinities decrease from top to bottom down groups. Summary of Trendīelow is a visual representation of electron affinity trends throughout the periodic table. Elements lower on the periodic table expel less energy upon the addition of an extra electron, giving the decreased exothermic nature of their electron affinities. Loosely bound electrons do not release as much energy upon joining an atom compared to to their tightly bound counterparts.
As we travel down a group, elements contain electrons further from their nuclei, and these electrons are bound less tightly. Electron proximity to these respective nuclei also influences this phenomenon, but contrary to the previous trend, electrons are placed in higher energy levels. Down GroupsĪs we travel down groups, electron affinities become more negative, meaning the process is more endothermic. These electrons exhibit a stronger attraction to the nuclei as a result of this proximity, explaining the exothermic nature of their electron affinities. Scientists attribute this pattern to the addition of electrons closer to the nuclei of these more rightward atoms.Īs elements trend to the right, the added electrons sit closer to their nuclei. Periodic Trends Across PeriodsĪs we travel from left to right on the periodic table, electron affinities become more positive- meaning that the electron attachment process is more exothermic. This results in positive second electron affinity values.
This endothermic process requires more energy than is released when an electron is added to the system. The second pertains to the addition of an electron to a negative ion. Because this exothermic process releases energy, first electron affinities are negative values. The first involves the addition of an electron to a neutral atom. There are two types of electron affinity, first and second. Essentially, electron affinity pertains to the energy changes that accompany the gain of one electron, and ionization energy those that accompany losing one electron. Ionization energies always involve the formation of positive ions, electron affinity energies describe the generation of negative ions.
It is the opposite of ionization energy, the energy required to ionize a gaseous atom and consequently remove an electron. We tend to liken electron affinity to an atom’s “likelihood,” or “chance,” of gaining an electron.
This process differs from electronegativity, which we define as the ability of an atom to attract an electron toward itself. Topics Covered in Other ArticlesĬhemists define electron affinity as the change in energy, measured in units of kJ/mole, experienced when an electron is added to a gaseous atom. In this tutorial about electron affinity, we will cover its definition, relevant periodic table trends, and factors that influence it.