Ionization energy

The ionization potential (also ionization, ionization potential, ionisation enthalpy ), the energy required to ionize an atom or molecule, i.e., an electron of the atom or molecule to be separated. They can be obtained by radiation of a high temperature material or supplied chemically.

General

After a pre- ionization of neutral atom or molecule has a positive electric charge. Previously balanced charge difference between the nucleus (s) and electron shell is shifted by the removal of an electron. One speaks of a positively ionized atom or molecule or a cation. This is characterized by a following superscript ' ' sign; For example, a sodium cation than Na in (Na is the chemical symbol for sodium).

As long as a cation or has electrons, it can be ionized by further supply of energy continues, but will provide the necessary energy to each additional ionization. In general, the nth ionization energy is the energy that is required in order to remove the nth electron. Symbolically, a multiply ionized cation is identified by a question put before the ' ' character number; For example, a 3 -fold ionized aluminum cation is referred to as Al3 .

Unit

A single electron which is given in eV ionization / atom, for 1 mol mole but in kJ / mol. The conversion factor is found to be from the conversion between eV and kJ and the Avogadro constant:

Where the " per atom" is usually omitted as here on the left.

First ionization energy and the periodic table

The first ionization energy depends on the force of attraction between the nucleus and the electron to be removed, which is calculated by the Coulomb formula:

With

• Classification or atomic number
• Elementary charge
• Distance of the electron from the nucleus
• Coulomb constant

Within a period, the first ionization energy strongly increases, although the increase from left to right goes discontinuous. Reason for the increase is the increasing atomic number and the consequent stronger attraction of the electrons by the nucleus. Although increases the number of electrons of the sheath within the period from the left to the right to the same extent to the respective adventitious electron but always installed in the same shell, the outer shell. The existing electrons can there not as strong shielding of the nuclear charge, because they have the same core as distance, the additional electron occupies the each adventitious electron reason. The increase in the nuclear charge can not therefore be compensated for by the increase in the charge of the electron cloud, so that the ionization energy increases. The discontinuous nature of the increase is particularly strong in the transition from nitrogen to oxygen. Here takes the ionization energy from left to right even. The reasons for such discontinuities can be interpreted with the atomic orbital model. So has nitrogen with its half-filled p subshell of a low-energy, stable electron configuration. For the removal of an electron is why a lot of energy is needed. Overall, the ionization energies of the alkali metals, the minimum and the ionization energies of the noble gases respectively represent respectively the maximum of the period dar. These extremes are lower in a group from top to bottom, as to be removed electron according to the shell model of the atom is on a new shell, thus increases its distance from the nucleus and less energy must be expended in order to release it from the attraction of the nucleus. Accordingly, takes the first ionization energy in the transition from one period to the next, eg from neon to sodium, abruptly.