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## Ionization potentialThe nth ionization energy is the energy required to strip it of an nth mole of electrons after the first n − 1 mole of electrons have already been removed. It is considered in physical chemistry as a measure of the "reluctance" of an atom or ion to surrender an electron, or the "strength" by which the electron is bound; the greater the ionization energy, the more difficult it is to remove an electron. The ionization potential is an indicator of the reactivity of an element. Elements with a low ionization energy tend to be reducing agents and to form salts.
## Additional recommended knowledge
## Values and trends*Main article:*Ionization energies of the elements
The next ionization energy involves removing an electron from an orbital closer to the nucleus. Electrons in the closer orbital experience greater forces of electrostatic attraction, and thus, require more energy to be removed. Some values for elements of the third period are given in the following table:
In order to determine how many electrons are in the outermost shell of an element, one can use the ionization energy. If, for example, it required 1,500 kJ/mol to remove one mole of electrons and required 6,000 kJ/mol to remove another mole of electrons and then 5,000 kJ/mol, etc. this means that the element had one electron in its outermost shell. This means that the element is a metal and in order for this element to achieve a stable complete outer shell, it looks to lose one electron. Thus, the first electron is easy to remove and consequently the ionization energy is low. Notice, however, that once the stable complete outer shell has been formed, it becomes ## Electrostatic explanationAtomic ionization energy can be predicted by an analysis using electrostatic potential and the Bohr model of the atom, as follows. Consider an electron of charge
Since the electron is negatively charged, it is drawn to this positive potential. (The value of this potential is called the
This analysis is incomplete, as it leaves the distance It is possible to expand this model considerably by taking a semi-classical approach, in which momentum is quantized. This approach works very well for the hydrogen atom, which only has one electron. The magnitude of the angular momentum for a circular orbit is:
The total energy of the atom is the sum of the kinetic and potential energies, that is:
Velocity can be eliminated from the kinetic energy term by setting the Coulomb attraction equal to the centripetal force, giving:
Now the energy can be found in terms of
Solving the angular momentum for
This establishes the dependence of the radius on
At its smallest value,
This can be expanded to larger nuclei by incorporating the atomic number into the equation.
## Quantum-mechanical explanationAccording to the more sophisticated theory of quantum mechanics, the location of an electron is best described as a "cloud" of likely locations that ranges near and far from the nucleus, or in other words a probability distribution. The energy can be calculated by integrating over this cloud. The cloud's underlying mathematical representation is the wavefunction which is built from a Slater determinant consisting of molecular spin orbitals. These are related by Pauli's exclusion principle to the antisymmetrized products of the atomic or molecular orbitals. This linear combination is called a configuration interaction expansion of the electronic wavefunction. In general, calculating the ## See also- Bragg-Gray Cavity Theory
- Electronegativity
- Ionization
- The
*ionization potential*is equal to the ionization energy divided by the charge of an electron. - The
*work function*is the energy required to strip an electron from a solid. - Ion
- Koopmans' theorem
- Di-tungsten tetra(hpp) has the lowest recorded ionization energy for a stable chemical compound.
- Electron affinity
Categories: Ions | Molecular physics | Atomic physics | Chemical properties | Quantum chemistry |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ionization_potential". A list of authors is available in Wikipedia. |