To proceed to determine the meaning of the term ionic radius, it is necessary, first of all, to record the etymological origin of the two words that give it its shape:
-Radio derives from Latin, from “radius”, which is equivalent to “ray of light” or “rod”.
-Ionic, for its part, emanates from Greek and can be translated as “relative to groups of atoms that are electrically charged.” Specifically, this word is the result of the sum of two main elements: “ion”, which is synonymous with “the one who walks”, and the suffix “-ico”, which is used to indicate “relative to”.
Radio it is a concept with multiple meanings. Today we are interested in taking the term as half the diameter of a circle. Ionic, for its part, is an adjective that refers to what is linked to ion (an atom or set of them that gains electrical charge from gaining or losing electrons).
The notion of ionic radius can be understood from atomic radio. The atomic radius is the mean distance between the nuclei of two atoms linked through a covalent bond. In the case of ionic radius, it is the radius that exists after the atom has obtained or given electrons. That is why this radius is associated with ions.
An ion, as we saw, has a charge, which can be negative or positive. Its origin is found in the tendency of chemical elements to resemble gas closer to the nobleman. Positively charged substances are known as cations, while negatively charged substances are the anions.
Within the world of chemistry, when one is talking about ionic radium, what comes to be established is that there can be two specific circumstances or that it has two fundamental properties: that the element in question proceeds to lose electrons or that, on the contrary, I won them.
That species that lost a electron, has a smaller ionic radius compared to the atomic radius, since the electrons experience a greater attraction towards the nucleus. Instead, the species that added an electron, has a higher ionic radius compared to the atomic radius (the built-in electron is not very attracted to the nucleus).
While the ionic radius increases with the decrease of a group, it is difficult to establish a trend regarding periods, because these depend on ions and there are elements with several possible ions.
In addition to all the above, it is necessary to make known that the aforementioned ionic radius does not have the particularity of presenting a clear tendency to what growth is at a specific and determined moment. What is this due to? In your case that depends on what the ion in question is.
Also referring to this circumstance, it must be stated that it is clearly marked by very important factors such as the effective nuclear charge, the atomic mass and even what is called atomic number.