Main Guide on Atomic Radius

Atomic radius of a chemical element is the distance between the nuclei of two similar atoms that are bonded together, generally the normal distance between the centre of the nucleus and the boundary of the surrounding electron shells. The atomic radius can be affected by the state or context of the atom.

Atomic Radius

Protons, electrons and protons are the three subatomic particles that make up an atom. The nucleus, which is made up of protons and neutrons, is at the heart of the atom, while electrons orbit in a little cloud around it. The entire distance between an atom’s nucleus and outermost orbital of its electron is measured in atomic radii.

The radius of an atom is comparable to the radius of a circle. The nucleus is like the centre of a circle, while the electron’s outermost orbital is like the circle’s outer edge. Due to the obvious uncertainty in the orientation of the outermost electron, determining the atomic radii is difficult.

Types of Atomic Radius

Covalent Radius

Radius of an atom under a covalent bond with some other atom(s) of a comparable element is called the covalent radius. The bond lengths between the pairs of covalently bound atoms can be used to calculate an atom’s covalent radius. The covalent radius is just 1 half of the bond length if the two atoms are of the same sort. While some compounds, such as Cl2  and O2, make this easy, others require inferring the covalent radius by comparing bond distances to atoms whose radii are known.

Metallic Radius

The radius of an atom linked by a metallic connection is called its metallic radius. In a metallic cluster, metallic radius is half of the total distance between the two adjacent atoms’ nuclei.

Ionic Radius

The radius of an atom creating an ion or an ionic bond is termed as the ionic radius. The electrons and nucleus are restricted by atomic bonds, and as a result, the ions or atoms do not have a fixed shape. The ionic radius is measured in Armstrong or picometers (pm). The radius can lie between 30 and 200 pm. The ionic radius is not constant; it varies depending on the electrons’ spin state, coordination number, and a variety of other factors. The size of an ion rises as the number of the coordinates increases. An ion with high spin state of an electron has a larger ionic size than the ion having a low spin state.

Vander-waals Radius

Vander-waals Radius is half the distance between the nuclei of 2 non – bonded comparable atoms that are isolated, as well as 2 adjacent similar atoms from surrounding atoms that are in the solid state. A weak magnitude force termed as venderwalls force connects these. In an ionic form, the ionic radius of chlorine is 360 pm, and the Vander-wall radius of chlorine atom is 180 pm.

Bohr Radius

The atomic radius of an atom in its lowest energy state is known as the Bohr radius. Bohr’s radius only applies to ions and atoms containing a single electron, such as hydrogen.

Atomic Radius in Periodic Table

As the number of electronic shells on an atom rises, it becomes larger. As a result, as one moves down the periodic table of elements, the radius of the atom grows. When moving from left to right for a period of time, the size of an atom normally decreases. Across a period, the atomic radius decreases while increasing down a group. The atomic radius of Francium is the biggest, whereas that of Helium is the smallest.

Variation of Atomic Radius Within a Group

The atomic radii of elements rise as the atomic number in a group increases from top to bottom. The principal quantum number rises as we proceed down the group. A new energy shell is added to each succeeding element. The valence electrons are moving away from the nucleus and away from nucleus. As a result, the attraction of the nucleus towards the electron lessens. Therefore, the atomic radius rises.

Conclusion

The atomic radius is the distance between centre of nucleus and the electron-carrying outermost shell. Atoms’ atomic radius shrinks from left to right over time. Atoms’ atomic radius increases from top to bottom inside a group in the same way. Atomic radius goes on increasing down a group. 

There are following types of atomic radius:

• Covalent Radius
• Metallic Radius
• Ionic Radius
• Vander-waals Radius
• Bohr Radius