Unlike some of these other properties, there are many exceptions to the trends for electron affinity. Like electronegativity, ionization energy, atomic or ionic radius, and metallic character, electronegativity displays periodic table trends. Electron Affinity Trend on the Periodic Table The energy value is equivalent, but the sign is reversed. However, some tables list values for the removal of an electron from a neutral atom rather than the capture of an electron. For noble gases, electron capture is endothermic. A noble gas atom is already stable, so it absorbs energy to capture another electron. For the noble gases, Δ E is positive and E ea is negative. So, for most atoms, Δ E is negative and E ea is positive. Basically, energy is required in order to attach an electron. The change in energy Δ E has a positive sign and the electron affinity E ea has a negative sign.Įlectron affinity for most atoms on the periodic table, except the noble gases, is exothermic. When atoms absorb energy, the reaction is endothermic.The change in energy Δ E has a negative sign and the electron affinity E ea has a positive sign. When atoms release energy, the reaction is exothermic.Use care, because the sign for the change in energy (Δ E) is the opposite of the sign for electron affinity ( E ea)! The sign of the energy change depends on whether you attach or remove an electron. How Electron Affinity Works (Sign Convention)Ītoms gain or lose energy when they gain or lose electrons or participate in chemical reactions. An atom with a more positive electron affinity value than another atom is an electron acceptor, while one with a less positive value is an electron donor. Electronic chemical potential and chemical hardness also use the principle of electron affinity. Mulliken applied electron affinities to list an electronegativity scale for the atoms of the periodic table. The reason electron affinity increases moving across a period is because the effective nuclear charge increases, which attracts electrons.Electron affinity increases moving across a period and sometimes decreases moving down a group.For most elements, except noble gases, this is an exothermic process.Electron affinity is the energy change when an atom gains an electron.Electron affinity also applies to molecules, in some cases. The most common units for electron affinity are kilojoules per mole (kJ/mol) or electronvolts (eV). The gas phase atom is used (rather than liquid or solid) because the atom’s energy levels aren’t influenced by neighboring atoms. In simple terms, it is a measure of a neutral atom’s ability to gain an electron. Analogically, it is possible to define the electron affinity for chemical compounds (molecules).This entry was posted on Augby Anne Helmenstine (updated on September 7, 2022)Įlectron affinity is a measure of how readily a neutral atom gains an electron.Įlectron affinity ( E ea) is the energy change when an electron is added to a neutral atom in the gas phase.Electronic affinity is measured (or calculated theoretically) for isolated atoms in gaseous state.This is the case, for example, in the case of sodium-chlorine (Na-Cl) bonding in sodium chloride. When this difference is large enough, the electron is virtually transferred from one atom to the other creating an ionic bond.

When two atoms form a chemical compound, the electron cloud is shifted towards the element with a higher electron affinity.

However, it may be slightly different for individual isotopes.

Electronic affinity is a property specific to a given element.

Such calculations can be made using quantum chemistry methods.

Theoretically, the value of the electron affinity can be approximated using Koopmans theorem as energy of lowest unocuppied orbital.

The electronic affinity is most often given in electron volts (eV) or in kilojoules per mole (kJ / mol).

Simply speaking, the greater the affinity of electrons, the more eagerly the atoms of a given element join electrons to form ions (anions).

Electron affinity is related to electronegativity of elements.

As a result of such attachment, a negative ion (anion) is formed.

The electronic affinity is amount of energy, that is released during the attachment of the electron to the neutral atom.

Electron affinity trend