Atomic Radii refer to the size of an atom, indicating how big or small an atom is. Atomic Radii or size, is defined as the shortest distance between the center of an atom’s nucleus and its outermost shell. This concept is similar to the radius of a circle, with the nucleus being analogous to the circle’s center and the outermost orbital of the electron corresponding to the circle’s outer edge. In this article, we will discuss various concepts related to atomic radii of various elements in detail.

What is Atomic Radii?

Atomic Radii, also known as atomic size or atomic radius, refer to the size of an atom.

Atoms are the fundamental building blocks of matter, and they consist of a central nucleus, composed of protons and neutrons, surrounded by a cloud of electrons.

In general, the atomic radii are defined as the total distance from the nucleus of an atom to the outermost electron orbital. Simplified, it can be described as something like the circle’s radius, with the electron’s outermost orbital at the circle’s outer edge and the nucleus in its center.

The net positive charge experienced by the valence electron in an atom is its effective nuclear charge or Z_eff. The valence electron does not sense the entire positive charge because part of it is shielded by the core electrons. Zeff has a significant impact on an atom’s atomic size. Because there is a greater screening of the electrons from the nucleus, which lessens the attraction between the nucleus and the electron, the atomic radius will expand as the Zeff lowers. As Zeff experiences a drop when moving down a group and from right to left across the periodic table, the atomic radius will experience a rise in these directions.

Atomic Radii Definition

Atomic radii is defined as the distance from the center of the nucleus to the outermost shell of electrons in an atom. It is often measured in picometers (pm) or angstroms (Å).

We also define the atomic radii of a chemical element as:

The mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons.

Types of Atomic Radii

Based on the type of bond, atomic radii is divided into three types as follows:

• Covalent Radius
• Ionic Radius
• Metallic Radius

Covalent Radius

The covalent radius represents the distance from the center of an atom’s nucleus to the point at which the electron cloud effectively ends, where it overlaps with another atom’s electron cloud in a covalent bond.

The covalent radius can be calculated when there is a covalent link between two atoms. Because the electrons are drawn to the same atoms equally when they are covalently bound, the radius of each atom equals half the distance between the two nuclei. An atom’s diameter can be found by measuring the distance between its two nuclei, but you want the radius, which is half the diameter.

Ionic Radius

Ionic radius refers to the size of an ion, which is an atom or group of atoms that has gained or lost electrons, resulting in a net electrical charge. An ion can be positively charged (cation) or negatively charged (anion), and its ionic radius can vary depending on the type of ion formed.

The ion with a positive charge will have a smaller size than the ion with a negative charge if we consider the charge of the ion.

Metallic Radius

Metallic radius, also known as the metallic atomic radius, refers to the size of an atom in a metallic solid or the context of metallic bonding.

The radius of an atom connected by a metallic connection is known as the metallic radius. In a metallic cluster, the metallic radius is half of the total distance between the nuclei of two neighboring atoms. Each atom in a metal will be the same distance apart since it is a collection of atoms of the same element.

Read More,

• Intermolecular Forces
• Atomic Mass of Elements

Other Types of Atomic Radii

Some of the other types of atomic radii include

• Van Der Waals Radius
• Bohr Radius

Let’s discuss these in detail as follows:

Van Der Waals Radius

It is defined based on the attractive forces between atoms or ions nearby when they are not bonded in a covalent or ionic manner.

Bohr Radius

The Bohr radius is defined as the radius of the orbit in which the electron of a hydrogen atom revolves around the nucleus in the lowest energy state. In other words, it represents the average distance between the electron and the nucleus.

Atomic Radii Formula

The formula for calculating the radii of any element is given as:

Atomic Radius = Distance between the two nuclei / 2

How to Determine Atomic Radii?

There are several ways to determine atomic radii of an element. Some important methods are discussed below:

1. X-ray Crystallography: This method involves analyzing the diffraction patterns produced when X-rays pass through a crystal.
2. Electron Diffraction: Electron diffraction involves firing electrons at a sample and analyzing the resulting diffraction pattern.
3. Coulomb’s Law: The atomic radius can be estimated using Coulomb’s law, which describes the electrostatic interaction between charged particles. For example, the distance between the nuclei of two bonded atoms in a molecule can provide an estimate of the atomic radius.

Atomic Radii for Elements

Here is a tabular description of approximate atomic radii for selected elements. The values are given in picometers (pm), where 1 picometer is equal to 1×10^-12 meters.