Steven Dutch, Natural and Applied Sciences, University
of Wisconsin - Green Bay
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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.
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At francium we begin adding a 7s orbital. Francium has one 7s
electron, radium has two. Radium is a direct alpha descendant on the U and Th decay chains, and is naturally abundant enough to be a problem in drinking water in places. Fr forms mostly by alpha decay in the U-235 decay chain, and has only very unstable isotopes, so at any given time there are only a few grams of it in the crust. |
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Like with the lanthindes, we start adding f orbitals, in this case
5f, but since the 5f and 6d orbitals are so similar in energy, the
addition of orbitals is even less orderly than the lanthanides. Contrary to widespread misconception, uranium is not the last naturally occurring element. Tiny amounts of primordial plutonium 244 (half-life 80 million years) have been discovered, and beta decays can probably create natural elements as high as americium or curium, in extremely tiny amounts. Americium is the heaviest element produced in macroscopic amounts, and is the isotope used to ionize air in smoke detectors. |
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What Atoms of Hydrogen Through Xenon Really
"Look Like"
What Atoms of the Heavy Elements Really "Look
Like"
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
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Created 26 April 2006, Last Update 14 Sep 2009
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