Osmium, density and relativity

Osmium, one of the platinum group metals, has a rather peculiar feature - is is inexplicably dense.

Osmium has a density of 22.59 grams/cm3, twice that of lead!

The problem is that chemically, it should not be possible to pack those atoms into that space. It has nothing to do with electron configuration or packing, which is, in essence, identical to that of the other platinum group metals. How can it be so dense, when it cannot be explained by conventional theories?

An observation: Well, it has been observed that the electrons in the 6s2 orbital, due the shape of the orbital, travel incredibly fast, in fact, approaching the speed of light.

The current (unproven) theory : Relativistic effects mean that the electrons, due to the speed, become much, much heavier, thereby increasing the attraction between electrons and the nucleus according to Newtonian physics, causing close packing and giving rise to the incredibly dense metal.

So far, the reason for Osmium's density is not known with certainty, so I thought I might just throw the idea out to all the other chemists on ATS to think about.

Originally posted by Saurus
Osmium, one of the platinum group metals, has a rather peculiar feature - is is inexplicably dense.

Osmium has a density of 22.59 grams/cm3, twice that of lead!

The problem is that chemically, it should not be possible to pack those atoms into that space. It has nothing to do with electron configuration or packing, which is, in essence, identical to that of the other platinum group metals. How can it be so dense, when it cannot be explained by conventional theories?

An observation: Well, it has been observed that the electrons in the 6s2 orbital, due the shape of the orbital, travel incredibly fast, in fact, approaching the speed of light.

The current (unproven) theory : Relativistic effects mean that the electrons, due to the speed, become much, much heavier, thereby increasing the attraction between electrons and the nucleus according to Newtonian physics, causing close packing and giving rise to the incredibly dense metal.

So far, the reason for Osmium's density is not known with certainty, so I thought I might just throw the idea out to all the other chemists on ATS to think about.

It's hardly unexplained. From the 1967 edition of the CRC Handbook of Chemistry and Physics:

"Calculations of the density from the space lattice which may be more reliable for these elements than actual measurements, however, give a density of 22.65 for iridium compared to 22.661 for osmium."

And it actually does have to do with electron configuration, but not in the 6s orbitals. It's a result of Lanthanide Contraction due to the configuration of the 4f orbitals.

Thank you for the reference. I will look into it and get back to you.