Difference Between Radical and Valency

The key difference between radical and valency is that radical is a chemical species that has an unpaired electron, whereas valency is a chemical concept that describes the ability of a chemical element to combine with another chemical element.

A radical is a very reactive chemical species because it has an unpaired electron. Valency is the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with.

1. Overview and Key Difference
2. What is Radical
3. What is Valency
4. Side by Side Comparison – Radical vs Valency in Tabular Form
5. Summary

What is Radical?

Radical is a chemical species which has an unpaired electron. The unpaired electron is a valence electron. That means; it is in the outermost shell of the atom. A radical can be an atom, molecule or an ion. Since the presence of an unpaired electron is unstable, the radicals are very reactive chemical species. Therefore, these chemical species have a very short lifetime.

Figure 01: Hydroxyl Radical

Further, radicals can generate in different ways. The typical method is redox reactions. Other important methods include ionizing radiation, heat, electrical discharges, electrolysis, etc. These radicals are intermediates of many chemical reactions.

What is Valency?

Valency is the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with. It is a chemical concept that measures the reactivity of a chemical element. However, it can describe only the connectivity of atoms, but it does not describe the geometry of a compound.

We can determine the valency of a chemical element by observing the position of that element in the periodic table. The periodic table has all the chemical elements according to the number of electrons in the outermost shell of the atom. The number of electrons in the outermost shell determines the valency of the atom as well. For example, group 1 elements in the periodic table have one outermost electron. Therefore, they have one electron for the displacement or the combination with a hydrogen atom; thus, the valency is 1.

Figure 02: Periodic Table

Furthermore, we can determine the valency using the chemical formula of a compound. Here, the basis of this method is the octet rule. According to the octet rule, an atom tends to complete its outermost shell by either filling up the shell with electrons or by removing the extra electrons. For example, if we consider the compound NaCl, the valency of Na is 1 because it can remove one electron that it has in the outermost shell. Similarly, the valency of Cl is also 1 because it tends to gain one electron to complete its octet.

However, we should not be confused with the terms oxidation number and valency because oxidation number describes the charge that an atom can carry with it. For example, the valency of nitrogen is 3, but the oxidation number can vary from -3 to +5.

What is the Difference Between Radical and Valency?

The key difference between radical and valency is that radical is a chemical species that has an unpaired electron, whereas valency is a chemical concept that describes the ability of a chemical element to combine with another chemical element. In terms of electrons, the difference between radical and valency is that radical has one unpaired electron, while the valency of a chemical element describes the electrons in the outermost shell.

Summary – Radical vs Valency

Reference:

1. “Radical (Chemistry).” Wikipedia, Wikimedia Foundation, 25 June 2019, Available here.

Image Courtesy:

1. “Hydroxyl radical” By SmokeyJoe – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Periodic table vectorial” By Rubén Vera Koster – Own work (CC BY-SA 4.0) via Commons Wikimedia