Introduction

An atom’s atomic radius and ionic radius are not fixed values. The distance between the nuclei of atoms and ions is affected by their configuration or stacking. Depending on the circumstances, atoms’ electron shells can overlap each other by varying distances. The “just barely touching” atomic radius is also known as the van der Waals radius because the distance between the atoms is determined by the weak attraction of van der Waals forces. This is the most common radius reported for noble gas atoms.

Metals covalently bonded form a lattice with covalent or metallic radius. The covalent radius is the distance between nonmetallic elements. Chart of ionic/atomic radii contains metallic, covalent, van der Waals radii. The minor differences in measured values should not be a cause for concern for the most part. It is important to know atomic/ionic radius, periodic trends, and why they exist.

 

Overview

Even though some people imagine atoms and ions as small, hard spheres resembling miniature table tennis balls or marbles, the quantum mechanical model tells us that their shapes and boundaries are much more ambiguous than those images suggest. As a result, atoms and ions do not have precise sizes; however, some atoms are larger or smaller than others, which influences their chemistry. The shape of atoms and ions complicates the concept of the ionic radius even more. While matter particles are frequently depicted as spheres, they are not always round. Chalcogen ions have been discovered to be ellipsoid in shape by researchers.

It is known that protons, neutrons, and electrons are the three subatomic particles that make up an atom. The nucleus of the atom is made up of protons and neutrons, and electrons orbit in a small cloud around the nucleus. The total distance from an atom’s nucleus to its electron’s outermost orbital is referred to as its atomic radii or atomic radius. The radius of an atom is comparable to the radius of a circle. The nucleus is analogous to the centre of a circle, and the electron’s outermost orbital is analogous to the circle’s outer edge. Because of the uncertainty in the position of the outermost electron, determining the atomic radii is difficult.

Ionic radii

In general, the ionic radius is the distance from an ion’s nucleus to which it exerts influence on its electron cloud.

Whenever an atom loses or gains electrons, ions form. If so, it becomes a cation; when an atom gains an electron, it becomes an anion. We can define the ionic radius as the distance between an ion’s nucleus and its outermost shell.

A cation’s atomic size will be smaller than that of the parent atom while an anion is slightly bigger than its parent atom. It is because of the fact that when an atom gains electrons, the total number of electrons increases, causing more repulsion between electrons and thus overshadowing the net effective nuclear charge.

Depending on their charge, ions can be larger or smaller than neutral atoms. When an atom loses an electron to form a cation, the lost electron no longer contributes to shielding the other electrons from the nucleus’ charge; as a result, the other electrons are more strongly attracted to the nucleus, and the atom’s radius shrinks. Similarly, when an electron is added to an atom to form an anion, the added electron repels other electrons, causing the atom to grow in size.

The ionic radius of a given ion is not a fixed property; rather, it varies with coordination number, spin state, and other parameters. We consider the ions to be as close to their ground state as possible for our purposes. Nonetheless, ionic radius values are sufficiently transferable to allow for the recognition of periodic trends.

Atomic radius and ionic radius

The atomic radius of a neutral atom is the distance between its nucleus and its outermost stable electron. In practise, the value is obtained by measuring and dividing the diameter of an atom in half. The radii of neutral atoms range from 30 to 300 pm, or trillionths of a metre.

The atomic radius is a standard measure of an atom’s size. This value, however, does not have a universally accepted definition. The ionic radius, covalent radius, metallic radius, and van der Waals radius are all examples of atomic radius.

Whereas the ionic radius is half the distance between two gas atoms that are in close proximity to one another. The values range from 30 pm to more than 200 pm. The atomic and ionic radius of a neutral atom is the same, but many elements exist as anions or cations. Because the atom loses an electron energy shell when it loses its outermost electron (positively charged or cation), the ionic radius is smaller than the atomic radius. If an atom gains an electron (negatively charged or anion), the electron usually falls into an existing energy shell, so the ionic radius and atomic radius are comparable in size.

Ionic radius periodic table

As we know, isoelectronic species are atoms and ions with the same number of electrons. For example, both O^2-, Mg²⁺ have ten electrons, but they do not have the same ionic radius because their effective nuclear charge is different.

The radius of a cation is lesser than that of an anion because a cation has a greater positive charge (i.e. more protons) and thus attracts the electrons in the outermost orbital with greater force, resulting in a smaller size.

Trends in Ionic Radius in Groups: Moving down a group in a periodic table, atoms add extra shells (number of electrons), causing the ionic radius of elements to increase.

Trends in Ionic Radius Across a Period: Atomic radius decreases, then increases, then decreases again due to cations and anions forming at start and end of a period.

FAQ’s

Q. What do you mean by ionic radius?

Ans: The ionic radius (plural: ionic radii) is a unit of measure of the ion of an atom in a crystal lattice. It equals half the distance between two ions that are barely touching.

Q. What affects ionic radius?

Ans: The size of an element’s ionic radius shows a similar trend on the periodic table. The ionic radius increases as you move down a column or group. This is due to the fact that each row adds a new electron shell. When moving from left to right across a row or period, it can be seen that the ionic radius decreases.

Q. What determines atomic radius?

Ans: Since an element’s atomic number increases, so does the size of its nucleus and the number of electrons surrounding it. An atom’s radius grows in direct proportion to its atomic number.