Ionization Energy Trend Ionization Energy Trend The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove electrons from gaseous atoms or ions. The property is alternately still often called the ionization potential, measured in volts. In chemistry it often refers to one mole of a substance (molar ionization energy or enthalpy) and reported in kJ/mol. In atomic physics the ionization energy is typically measured in the unit electron volt (eV). Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies. The ionization energy is different for electrons of different atomic or molecular orbitals. More generally, the nth ionization energy is the energy required to strip off the nth electron after the first electrons have been removed. Ionization energies for all charge states of all elements with atomic numbers at and below that of lead are tabulated in the Atomic Data and Analysis Structure (ADAS) database. It is considered a measure of the tendency of an atom or ion to surrender an electron, or the strength of the electron binding; the greater the ionization energy, the more difficult it is to remove an electron.
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The ionization energy may be an indicator of the reactivity of an element. Elements with a low ionization energy tend to be reducing agents and form cations, which in turn combine with anions to form salts. Electron binding energy (BE), more accurately, is the energy required to release an electron from its atomic or molecular orbital when adsorbed to a surface rather than a free atom. Binding energy values are normally reported as positive values with units of eV. The binding energies of 1s electrons are roughly proportional to (Z-1)² (Moseley's law). Factors affecting the ionization process The amount of ionization process depends on the nature of radiation energy and the interacting material. The amount of ionization process can vary with varying levels of radiation energy for a particular material. The two main factors are described as below. 1. Density of material <<--- The radiation photons of the same energy are not penetrated a given material up to the same depth. <<--- Some of the photons lose their energy by collision while some may pass through the material without any interaction. <<--- The depth of penetration of photon energy depends upon material density or atomic structure. <<--- The depth of radiation penetration decreases with increasing the density of material. <<--- The absorption process of radiation continues till it becomes deep in to material. <<--- There is a specific level for each material at which the radiation intensity becomes one half.
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<<--- This depth of level is known as Half Value Layer (HVL). 2. Radiation energy <<--- The depth of penetration increases with increasing the energy of radiation. <<--- This is due to increase the half value layer. <<--- So the radio isotopes are used to produce the high energy radiation for ionization process. <<--- Radio isotopes can be produced by neutron activation, separation of fission product, and bombardment of charged particle. <<--- These are the isotopes which are radioactive and unstable. Ionization Energy Trend The ionization process requires a sufficient amount of energy for removing of an electron. The removal of first electron needs the least amount of energy while more energy is needed for removal of electron from a positively charged ion. The (n+1)th ionization energy is mostly higher than the nth ionization energy. The next ionization energy involves the removal of electron from the orbitals which is close to nucleus. These electrons experience greater forces of electrostatic attraction so their removal needs more energy. Generally metals have tendency to lose electrons and form a positive ions. But the nonmetals have high ionization energies. This is due to the strong attractions of non metals for their valence electrons.
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