# What is the atomic radius of chlorine?

I'm trying to study for chemistry and there's a question in my book about identifying an element based on its atomic radius. But when I looked up the value for chlorine, I found different answers from different sources:

What is the correct value?

• According to the environmentalchemistry website, the unit is angstroms (the value 0.97 is equivalent to 97 pm) – JavaScriptCoder Jan 10 '18 at 22:48

There is no such thing as unified atomic radius. An atomic radius is a class consisting of van der Waals radii $R_\mathrm{vdW}$ (steric interactions), covalent radii $R_\mathrm{cov}$, and ionic radii $R_\mathrm{i}$ (and some other as well).

From the recent edition of CRC Handbook [1, p. 9-57]:

$$\begin{array}{llrr} \hline \text{Element} & \text{Symbol} & R_\mathrm{vdW}~(Å) & R_\mathrm{cov}~(Å)\\ \hline \text{Chlorine} & \ce{Cl} & 1.75 & 1.00\\ \hline \end{array}$$

Ionic radii are given for the crystallographic data separately [1, p. 12-12]:

$$\begin{array}{llr} \hline \text{Ion} & \text{C.N.} & R_\mathrm{i}~(Å)\\ \hline \ce{Cl^{+5}} & 3~\text{(pyramidal)} & 0.12\\ \ce{Cl^{+7}} & 4 & 0.08\\ \hline \end{array}$$

### Reference

1. Haynes, W. M.; Lide, D. R.; Bruno, T. J. CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data.; 2017; Vol. 97. ISBN 978-1-4987-5429-3.
• Related: Pyykkö's summary of covalent radii, see my answer here. – Martin - マーチン Jan 11 '18 at 10:37
• @Martin-マーチン - Agreed. I think I've linked to Pyykkö's radii in other questions too. – Geoff Hutchison Jan 11 '18 at 16:34