The key difference between covalent radius and metallic radius is that the covalent radius is half the distance between two homonuclear atoms that are in a covalent bond, whereas the metallic radius is half the distance between two adjacent metal ions in a metallic structure.
Both covalent radius and metallic radius are half the distances between atomic nuclei; in covalent radius, we consider atoms of the same chemical element having a single covalent bond between them, while in metallic radius, we consider adjacent metal ions.
CONTENTS
1. Overview and Key Difference
2. What is Covalent Radius
3. What is Metallic Radius
4. Side by Side Comparison – Covalent Radius vs Metallic Radius in Tabular Form
5. Summary
What is Covalent Radius?
Covalent radius is half of the internuclear separation between the nuclei of two single-bonded atoms of the same species. That means; the covalent radius is equal to the half of the distance between two homonuclear atomic nuclei and these atoms have a single covalent bond between them. We can denote it by rcov. Generally, we measure this value using X-ray diffraction methods. Sometimes, we may have to measure the covalent radius for chemical elements having multiple allotropes. There, we can determine the radius by taking the average of bond distances between atoms in each allotrope. Moreover, the values for this measurement are in picometer (pm) or angstrom scale. However, we should not confuse covalent radiant with covalent distance, which is the total distance between the atomic nuclei of two atoms.
Figure 01: Covalent Distance and Covalent Radius
What is Metallic Radius?
Metallic radius is half the distance between two adjacent metal ions in a metallic structure. The value of this radius depends on the nature of metal ions and the environment of them as well. Further, the metallic radius decreases along a period of the periodic table. It is due to the increase of effective nuclear charge. Moreover, the metallic radius increases down a group in the periodic table because the principle quantum number increases down a group.
What is the Difference Between Covalent Radius and Metallic Radius?
The key difference between covalent radius and metallic radius is that the covalent radius is half the distance between two homonuclear atoms that are in a covalent bond, whereas the metallic radius is half the distance between two adjacent metal ions in a metallic structure. Further, we consider two atoms of the same chemical element when measuring the covalent radius, but in metallic radius, we consider two metal ions that are adjacent to each other in a metallic structure.
Moreover, there are no particular trends for the covalent radius of chemical elements, but for metallic radius, the radius decreases along a period and increases down the group of the periodic table. So, we can consider this too as a difference between covalent radius and metallic radius.
Summary – Covalent Radius vs Metallic Radius
Covalent radius and metallic radius are two different terms. In short, the key difference between covalent radius and metallic radius is that covalent radius is half the distance between two homonuclear atoms that are in a covalent bond, whereas metallic radius is half the distance between two adjacent metal ions in a metallic structure.
Reference:
1. Helmenstine, Anne Marie, Ph.D. “What Is the Difference Between Atomic Radius and Ionic Radius?” ThoughtCo, Dec. 5, 2018, Available here.
2. Libretexts. “Covalent Bond Distance, Radius and Van Der Waals Radius.” Chemistry LibreTexts, Libretexts, 5 June 2019, Available here.