While ionization energy is the energy change incurred from losing an electron, electron affinity is the energy change incurred from gaining an electron. This affinity is known as the first electron affinity and these energies are negative. These values are represented with a negative sign. Cl (g) + e-→Cl-(g) For most atoms, this is a negative quantity - or energy is released. Electron affinity of a molecular entity is the measure of energy difference between its standard form and its anionic form with one additional electron. Here are the electron affinities of the 16th and 17th groups. The electronic affinity is amount of energy, that is released during the attachment of the electron to the neutral atom. By convention, the negative sign shows a release of energy. Electron Affinity: Abundance in the Ocean: Electron Configuration: Abundance in the Sun: Electronegativity: Abundance in the Universe: Half Life: Atomic Mass: Heat of Fusion: Atomic Number: Heat of Vaporization: Atomic Radius: Ionization Energies: Boiling Point: Melting Point: It is not easy to discern many obvious regularities in this table, especially since some of the electron-affinity values quoted are negative, indicating that energy is sometimes required to force an extra electron onto an atom. In smaller atoms, the newly added electron is attracted strongly by the nucleus and hence their electron affinity values are higher. Nevertheless, it is quite obvious which of the periodic groups correspond to the highest electron affinities. In general, these values increase with decrease in the size. Electron affinity, in chemistry, the amount of energy liberated when an electron is added to a neutral atom to form a negatively charged ion.The electron affinities of atoms are difficult to measure, hence values are available for only a few chemical elements, chiefly the halogens. When an electron is added to a neutral atom, energy is released. Since this is a released energy, it is a negative entity.This applies only to first electron affinity, however, the second electron affinity is not necessary a released energy, most of the times for an atom to attract a second electron, it requires energy and therefore, it is a positive entity. Electron Affinity of Chemical Elements. Electron affinity by definition is the amount of energy released when an atom attracts an electron. Greater the negative value greater is the electron affinity. As a result of such attachment, a negative ion (anion) is formed. What is electron affinity? C + e – → C – – ∆H = Affinity = 153.9 kJ/mol. For some elements, however, this is … Thus, large electron affinity value indicates the tendency of forming stable negative ions and low electron affinity values indicate tendency to form positive ions. To use electron affinities properly, it is essential to keep track of sign. Electron affinity is related to electronegativity of elements.Simply speaking, the greater the affinity of electrons, the more eagerly the atoms of a given element join electrons to form ions (anions). The general trend for electron affinity down the group is that it decreases because of the increase in atomic radius.The exception of $\ce{Cl}>\ce{F}$, I can understand is because fluorine has a high electron density and it is unfavourable to add more electrons as it would only increase the electron -electron repulsion. 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