![]() ![]() The usual expression for calculating E ea when an electron is attached isĮ ea = ( E initial − E final) attach = −Δ E(attach) Negative values typically arise for the capture of a second electron, but also for the nitrogen atom. In this case, the electron capture is an endothermic process and the relationship, E ea = −Δ E(attach) is still valid. However, if the value assigned to E ea is negative, the negative sign implies a reversal of direction, and energy is required to attach an electron. The relation between the two is E ea = −Δ E(attach). Confusion arises in mistaking E ea for a change in energy, Δ E, in which case the positive values listed in tables would be for an endo- not exo-thermic process. It is the word "released" within the definition "energy released" that supplies the negative sign to Δ E. The positive values that are listed in tables of E ea are amounts or magnitudes. Electron capture for almost all non- noble gas atoms involves the release of energy and thus are exothermic. For any reaction that releases energy, the change Δ E in total energy has a negative value and the reaction is called an exothermic process. To use electron affinities properly, it is essential to keep track of sign. Together they may undergo charge-transfer reactions. ![]() Another example, a molecule or atom that has a more positive value of electron affinity than another is often called an electron acceptor and the less positive an electron donor. Other theoretical concepts that use electron affinity include electronic chemical potential and chemical hardness. Mulliken to develop an electronegativity scale for atoms, equal to the average of the electronsĪffinity and ionization potential. This property is used to measure atoms and molecules in the gaseous state only, since in a solid or liquid state their energy levels would be changed by contact with other atoms or molecules.Ī list of the electron affinities was used by Robert S. Measurement and use of electron affinity 4 "Electron affinity" as defined in solid state physics.1 Measurement and use of electron affinity.The chemical rationale for changes in electron affinity across the periodic table is the increased effective nuclear charge across a period and up a group.Įlectron affinity: The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion.Įlectronegativity: The tendency of an atom or molecule to attract electrons to itself.Electron affinity generally increases across a period in the periodic table and sometimes decreases down a group. There are general trends in electron affinity across and down the periodic table of elements.The electron affinity of an atom or molecule is the propensity for that particle to gain an electron.Electron affinity follows the trend of electronegativity: fluorine (F) has a higher electron affinity than oxygen (O), and so on.Īpplications of Hard-Soft Acid-Base theoryĬhemistry Question Pack Passage 1 Question 4 However, this trend applies only to Group-1 atoms. Since this electron is farther away, it should be less attracted to the nucleus and release less energy when added. A trend of decreasing electron affinity down the groups in the periodic table would be expected since the additional electron is entering an orbital farther away from the nucleus. Chlorine has the highest electron affinity while mercury has the lowest.Įlectron affinity generally increases across a period (row) in the periodic table, due to the filling of the valence shell of the atom. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values. Atoms, such as Group 7 elements, whose anions are more stable than neutral atoms have a higher electron affinity. Generally, nonmetals have a more positive electron affinity than metals. This can be shown for the chloride ion formation below: The electron affinity (E ea) of a neutral atom or molecule is defined as the amount of energy released when an electron is added to it to form a negative ion. Electron affinity is the energy change that occurs when a neutral atom gains an electron. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |