Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
Although almost any chemical reference will have data on ionic radii and electron configuration, and tabulations of energy levels are not hard to find, there is little readily available data on the relative sizes of orbitals. Ionic radii are useful in crystal modeling, electron configuration and energy levels for all kinds of stuff, but sizes of orbitals don't seem to have much practical use.
It's impossible to measure the sizes of orbitals and even of atoms directly. You measure macroscopic objects basically by bouncing light off them (say off the object and a ruler) but wavelengths tiny enough to show atomic structure in detail (nanometers and less) are energetic enough to destroy what you want to see. It's like measuring the size of a figurine by swinging a hammer. Ionic radii are calculated from atomic spacings in materials. Orbital radii principally come out of theories whose main purpose is to account successfully for the other properties of atoms. These drawings are based on data from J. T. Waber and D. T. Cromer, Orbital Radii of Atoms and Ions, Journal of Chemical Physics, 15 June, 1965, vol. 42, no. 12, p. 4116-4123. The sizes shown are the radii of the maximum electron density, so the actual extent of significant electron density is maybe 50% larger.
All the drawings are to common scale. For orbitals with lobes, the principal lobes are shown but there is no attempt to portray the complex inner structure. It gets plenty busy in toward the center of the atom anyway.
|In cesium and barium we add a 6s orbital. Cesium has one 6s electron, barium has two.|
|For the lanthanides, for the first time, we begin adding 4f orbitals. However, the 4f and 5d orbitals are so similar in energy that it's not a perfectly predictable process. Lanthanum, Gadolinium and lutetium add 5d orbitals instead of 4f.|
|These elements add 6p electrons. They're grouped like this for consistency with previous groups of elements, but thallium and lead are perfectly respectable (if very toxic) metals and bismuth is also pretty metallic. Bismuth is the basis for the "bis" in Pepto-Bismol .
After bismuth, all three 6p orbitals are present and the orbitals fill out by adding second electrons. Radon has the complete stable outer octet and is a noble gas.
What Do Atoms Really "Look Like?"
What Atoms of Hydrogen Through Xenon Really "Look Like"
What Atoms of the Heavy Elements Really "Look Like"
Scale Drawings of Atoms and Orbitals: Hydrogen Through Krypton
Scale Drawings of Atoms and Orbitals: Rubidium Through Xenon
Scale Drawings of Atoms and Orbitals: Cesium Through Radon
Scale Drawings of Atoms and Orbitals: Francium Through Lawrencium
What the Atomic Structures of Some Simple Materials Really "Look Like"
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Created 26 April 2006, Last Update