Definition of Periodic Properties (Atomic Radius, Ionic Radius, PI, and Electroaffinity)

Atomic radio

With the value of the atomic radius we define the distance existing between two nuclei of bonded atoms. While metals form networks of atoms equal to each other, nonmetals form molecules linking different elements, therefore, in these cases it depends fundamentally on the strength of the link that makes them more or less attracted to each other.

How is the trend according to the atomic number? Well, within the same period, as the atomic number increases, we increase protons in the atomic nucleus and electrons located at the same level of Energy, so the shielding effect of the electrons of the internal configuration does not vary. For this reason, the effective nuclear charge on the

electron outermost increases and hence the atomic radius decreases. Whereas, by increasing the atomic number in the same group of the Periodic table, the protons in the nucleus increase, but so do the electrons, locating at levels further away from the nucleus, with which, the effective nuclear charge on the outermost electron is always the same and, therefore, the atomic radius increases.

Ionic Radius

Ionic radius allows the study of the binding energies involved in ionic compounds, known as Lattice Energy. That is why it is important to understand how to analyze the radius of an anion or cation.

When a neutral element loses one or more electrons, it has a high charge in its nucleus that will attract more strongly the electrons. electrons that it conserves, so when losing valence electrons the radius of the ion is less than the radius of the atom neutral. The reverse occurs when a neutral element gains electrons, forming an anion. The species negatively charged incorporated new electrons conserving the same charge in its nucleus, so that the radius of the ion is greater than the radius of the neutral atom of the preceding one.

When isoelectronic species are studied, such as: Na⁺; Mg⁺² and Ne, all these species have 10 electrons in their electronic configuration; however, Na + has 11 protons in its nucleus while Mg⁺² 12 protons and the Ne 10 protons. This explains why Ne is larger than Na⁺ and these larger than Mg⁺². Faced with the same electron configuration, the species that has more protons will have more charges that will attract electrons and, consequently, the radius decreases.

Both ionic and atomic radii are measured in picometers and are tabulated.

Ionization Potential

It represents the minimum energy that must be delivered to an element in a gaseous state (in its fundamental state) in order to rip an electron from it.

How is the trend according to the atomic number? When we increase the atomic number in a period, the ionization energy increases since, as we saw, the atomic radius decreases due to the increase in the nuclear charge, therefore, it is logical to think that removing an electron will imply giving up more energy. Whereas, when increasing the atomic number in a group, the atomic radius increases, therefore, the potential of first ionization decreases.

If the formation of the ion positive results in higher stability, the ionization energy will be lower, for example, the case of metals where, by losing electrons, they adopt the electronic configuration of the nobler gas more near. If the new electron configuration gives the species additional stability, the ionization potential is reduced, such is the case of species that by losing one or more electrons adopt configurations with layers half-filled.

We speak of energy of first, second, third ionization energy as one or more electrons are desired to be removed.

Electroaffinity

It is a property related to the energy involved in the process, which gives an idea about the tendency of an atom to form an anion. Again, we refer to the atom in a gaseous and fundamental state. The more energy the process releases, the easier it will be to form the anionic species.

Consider the halogens, which when forming an anion adopt some additional stability by resembling their electronic configuration to that of a noble gas. Here the electron affinity increases.

Therefore, electron affinity increases over a period when the atomic number increases and, throughout a group, when the atomic number decreases.

Topics in Periodic Properties (Atomic Radius, Ionic Radius, PI, and Electroaffinity)