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?

  • 1
    $\begingroup$ According to the environmentalchemistry website, the unit is angstroms (the value 0.97 is equivalent to 97 pm) $\endgroup$ 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]:

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


  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.
  • 2
    $\begingroup$ Related: Pyykkö's summary of covalent radii, see my answer here. $\endgroup$ Jan 11 '18 at 10:37
  • $\begingroup$ @Martin-マーチン - Agreed. I think I've linked to Pyykkö's radii in other questions too. $\endgroup$ Jan 11 '18 at 16:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.