Ionization energy is the main characteristic of an atom. It determines the nature and strength of the chemical bonds that an atom is capable of forming. The reducing properties of a substance (simple) also depend on this characteristic.
The concept of "ionization energy" is sometimes replaced by the concept of "first ionization potential" (I1), meaning the smallest energy that is needed to move an electron away from a free atom when it is in a state of energy called the lowest.
In particular, for a hydrogen atom, this is the name of the energy that is required to detach an electron from a proton. For atoms with several electrons, there is the concept of a second, third, etc. ionization potentials.
The ionization energy of a hydrogen atom is the sum, one term of which is the energy of an electron, and the other is the potential energy of the system.
In chemistry, the energy of a hydrogen atom is denoted by the symbol "Ea", and the sum of the potential energy of the system and the energy of the electron can be expressed by the formula: Ea = E + T = -Ze / 2.R.
From this expression it can be seen that the stability of the system is directly related to the charge of the nucleus and the distance between it and the electron. The smaller this distance, the stronger the charge of the nucleus, the stronger they are attracted, the more stable and stable the system, the more energy must be spent on breaking this connection.
Obviously, by the level of energy spent to break the bond, one can compare the stability of systems: the more energy, the more stable the system.
The atomic ionization energy - (the force that is necessary for breaking bonds in a hydrogen atom) was calculated experimentally. Today its value is known for sure: 13.6 eV (electron-volt). Later, scientists, also using a series of experiments, were able to calculate the energy required to break the atom-electron bond in systems consisting of a single electron and nucleus with a charge twice the charge of a hydrogen atom. It was established experimentally that in this case 54.4 electron-volts are required.
The well-known laws of electrostatics state that the ionization energy necessary to break the bond between opposite charges (Z and e), provided that they are located at a distance R, is fixed (determined) by this equation: T = Ze / R.
Such energy is proportional to the magnitude of the charges and, accordingly, is inversely related to the distance. This is quite natural: the stronger the charges, the stronger the forces connecting them, the more powerful the force required to exert in order to break the connection between them. The same applies to distance: the smaller it is, the stronger the ionization energy, the more pitchfork will have to be applied to break the bond.
This reasoning explains why a system of atoms with a strong nuclear charge is more stable and needs more energy to detach an electron.
The question immediately arises: "If the charge of the nucleus is only twice as strong, why does the ionization energy needed to detach an electron increase not two, but four times? Why is it equal to twice the charge taken in a square (54.4 / 13.6 = 4 )? ".
This contradiction is explained quite simply. If the charges Z and e in the system are relatively in a mutual state of immobility, then the energy (T) is proportional to the charge Z, and they increase proportionally.
But in a system where an electron with a charge e makes revolutions of a nucleus with a charge Z, and Z amplifies, the radius of rotation R decreases proportionally: the electron is attracted to the nucleus with greater force.
The conclusion is obvious. The ion charge acts on the ionization energy, the distance (along the radius) from the nucleus to the highest point of the charge density of the external electron; the repulsive force between external electrons and a measure of the penetrating ability of an electron.