Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Atomic Radii of Isotopes
Name: John Eric M.
Status: other
Age: old
Location: N/A
Country: N/A
Date: 5/28/2003


Question:
In a discussion in Sciforum I have not been able to get a clear answer on the atomic radii of isotopes. Have they been measured or is it an assumption that they are the same as the element with the same atomic number? I have check the library and web, where the isotope tables show only the mass. I am aware that the outer electron orbits are the same for element and isotope but, I assume that as atoms and particles are fields, the addition of a neutral field (neutron) could increase the volume without altering the radii of outer electrons as the electron orbit is determined by the magnetic structure.


Replies:
To a good approximation the atomic radii of isotopes are all the same. The major interaction holding atoms together is electrostatic attraction of the oppositely charged nucleus and the various electrons. Since the neutron has no charge, there is no electrostatic attraction between an electron and a neutral particle, the atomic radius will not change. There are other much weaker interactions that can have a small effect -- spin on the electron interacting with the spin on the nucleus (if it has one), orbital angular momentum of the electron interacting with spin on the nucleus (if it has one). Possible relativistic effects too. However, other "minor" interactions have a larger effect than these -- specifically electron / electron interactions. So while one could calculate (I suppose) the isotope effect on atomic radius, it would be very small. I don't recall ever seeing the results of such a calculation because it could only be done on atoms containing very few electrons to not be "swamped" by the electron / electron effects.

Vince Calder


There must be some small effect.

I do know of the effect of isotopes on the dimensions of crystals of atoms. The atoms all attach themselves in a regular manner, a crystal structure. This mainly would have to do with the size of the atom, its chemical bonding etc, but has a tiny isotope effect, see Physical Review B, Vol 38, No. 8,9/15/1988, Effect of isotope concentration on the lattice parameters of germanium perfect crystals, R.C. Buscheret et. al.

Steve Ross



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory