I was curious about which was the densest nuclide.

I thought this would be pretty straightforward since for a given allotrope of a given element at a given temperature and pressure, the number of moles per volume is very close to independent of isotope. (For elements of low atomic number, this is less true, but all the candidates for densest nuclide are from elements of high atomic number, as you may have guessed.)

But it turns out that the elemental density estimates vary greatly from one reference source to the next, much more than I’d anticipated. I realise the density of samples will vary but I thought they’d have a pretty good lid on the mean density at STP of the lowest enthalpy allotrope given average crustal isotope composition.

Examples for Iridium and Osmium
Webelements: 22650 22610
Lenntech: 22400 22600
Chemistry.wikia: 22560 22590

These are all supposed to be lowest enthalpy allotrope, standard temperature and pressure. I thought it might be because they were using different isotopic compositional bases but their atomic mass values were completely identical. Shit, webelements gives iridium’s density as being greater than osmium’s. You had one job, internet.

dv said:

I was curious about which was the densest nuclide.

I thought this would be pretty straightforward since for a given allotrope of a given element at a given temperature and pressure, the number of moles per volume is very close to independent of isotope. (For elements of low atomic number, this is less true, but all the candidates for densest nuclide are from elements of high atomic number, as you may have guessed.)

But it turns out that the elemental density estimates vary greatly from one reference source to the next, much more than I’d anticipated. I realise the density of samples will vary but I thought they’d have a pretty good lid on the mean density at STP of the lowest enthalpy allotrope given average crustal isotope composition.

Examples for Iridium and Osmium
Webelements: 22650 22610
Lenntech: 22400 22600
Chemistry.wikia: 22560 22590

These are all supposed to be lowest enthalpy allotrope, standard temperature and pressure. I thought it might be because they were using different isotopic compositional bases but their atomic mass values were completely identical. Shit, webelements gives iridium’s density as being greater than osmium’s. You had one job, internet.

What a load of rubbish!

But, I have decided to go with chemistry.wikia because their values seem to agree with estimates of molar density based on crystallographic analysis.

22646 Ir-193
22795 Os-192
21767 Pt-198

I guess you’re only looking at stable / natural nuclides.

Elements 108 & 109, hassium & meitnerium, the homologues of osmium and iridium, make normal elements look like fairy floss. :)

According to Wikipedia,
Hassium has an estimated density of 40.7 g/cm³
Meitnerium has an estimated density of 37.4 g/cm³

The most stable isotopes of these elements have relatively long half-lives (especially hassium), but I suspect they are still far too short for large enough samples to be synthesized to enable accurate direct density measurements.

Yes, it’s not just that they don’t last long enough: their radioactivity is so high that they are always too hot to even form a solid. Those estimates are largely theoretical.

I was considering those nuclides that were basically safe to handle. Os-194 has a half-life of 6 years: long enough to be able to study a large enough sample and for a solid to form, but too short for it to be safe to use in industrial applications, so I left it out, as I did some of the higher Iridium ‘topes.

So the end result is that, the densest nuclide that would be safe enough for industrial use would be Os-192, which is about 0.9% denser than ordinary osmium, which is a mix of isotopes from Os-184 to Os-192.

Bubblecar said:

See, that’s the kind of thing you would not want to try with Hassium, regardless of its superior density.

Let’s make one for Baby Mutant.

dv said:

But, I have decided to go with chemistry.wikia because their values seem to agree with estimates of molar density based on crystallographic analysis.

22646 Ir-193
22795 Os-192
21767 Pt-198

My copy of the Handbook of Chemistry and Physics gives densities at melting point:
Iridium 19
Osmium 20
Platinum 19.77
These look like measured values to me.

mollwollfumble said:

dv said:

But, I have decided to go with chemistry.wikia because their values seem to agree with estimates of molar density based on crystallographic analysis.

22646 Ir-193
22795 Os-192
21767 Pt-198

My copy of the Handbook of Chemistry and Physics gives densities at melting point:
Iridium 19
Osmium 20
Platinum 19.77
These look like measured values to me.

mollwolfumble … it should be obvious to you that the densities at melting point are going to be lower than the densities at room temperature.