Intermediate Topic 217 of 1102 Bonding & Molecular Structure
Covalent Radius
Half the bond length between two identical bonded atoms.
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In-depth explanation of Covalent Radius
The covalent radius is half the bond length between two identical atoms joined by a single covalent bond. It allows the length of bonds between different atoms to be estimated, since a bond length is approximately the sum of the two covalent radii. The additivity is approximate, because bonds between atoms of different electronegativity are slightly shorter than the simple sum predicts. Covalent radii decrease across a period and increase down a group, following the general trends in atomic size. They are derived from X-ray and spectroscopic data.
Going deeper: Covalent Radius
Key ideas: Use additivity: C-H is 77 plus 37 gives 114 versus 109 measured, so subtract about 0.09 times the electronegativity difference (Schomaker-Stevenson correction). Multiple bonds have smaller radii: carbon 77 pm single, 67 double, 60 triple. Trend: decreases left to right (from effective nuclear charge) and increases down a group.
Common mistakes and connections: Students use the metallic radius or the van der Waals radius by mistake, or double the radius of a single atom rather than halving a bond length. Another is forgetting the correction for polar bonds. Radii are not absolute properties: they depend on bond order. Links to bond length, atomic radius trends, electronegativity and ionic radii.
Visualization of Covalent Radius
Covalent radius, half the single bond length of an X-X bond, shrinks across period 2 as nuclear charge rises, and is larger for chlorine. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The Cl-Cl bond length of 199 pm gives a covalent radius of about 99.5 pm for chlorine.
Frequently asked questions about Covalent Radius
What is Covalent Radius?
Half the bond length between two identical bonded atoms.
Is Covalent Radius a beginner, intermediate or advanced topic?
Covalent Radius is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
What should I learn before Covalent Radius?
Study these earlier topics in Bonding & Molecular Structure first: Three-Center Two-Electron Bond, Banana Bonds, Van der Waals Radius.
What comes after Covalent Radius?
The next topics in Bonding & Molecular Structure are Electron-Pair Repulsion Ranking and Bent's Rule.
Can I practise Covalent Radius with quizzes?
Yes. The interactive lesson includes a self-check question on Covalent Radius, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Covalent Radius fits in Bonding & Molecular Structure
Covalent Radius is topic 102 of 104 in Bonding & Molecular Structure.