Odd molecule

Odd molecule is a term invented by Gilbert N. Lewis in 1916 for a molecule containing an odd number of electrons.

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Taking the p-shell elements, such molecules are rare; they are usually colored and paramagnetic, that is, attracted by a magnet.

Odd molecules are 'radicals.'

A fine example is nitric oxide, q.v.; nitrogen dioxide is another; chlorine dioxide is also an example, being a reddish-yellow gas. They are all fairly reactive.

When including d-shell elements, i.e., the transition metals, the concept mostly doesn't apply, and this 'odd' state is not so unusual.

References

• "The Atom and the Molecule", Gilbert N. Lewis, Journal of the American Chemical Society, volume 38 (1916), pages 762–786; received January 26, 1916.
• "Classic Papers" - online copy of 1916 paper - 2005-V-17