Talk:Astatine

Density of orthorhombic astatine (speculation)

When solid, Cl, Br and I have orthorhombic crystalline structures. The volumes of the respective unit cells are 230.91, 262.1046 and 341.5684 cubic Å. The crystalline atomic radii are 0.99, 1.135 and 1.345 Å. If astatine instead has an (unmetallic) orthorhombic structure, its unit cell volume can be indicatively extrapolated using the cube of its predicted covalent atomic radius of 1.5 Å. Its crystalline atomic radius may be marginally larger due to intralayer bonding, as appears to occur in iodine, but I’ll ignore this possibility as I have no way of quantifying it. A straight line extrapolation (R-squared = 0.9989) of unit cell volume for Cl, Br, and I vs. the cube of atomic radius for Cl, Br, I and At indicates an atomic volume for At of 412.3276. There are eight atoms in an orthorhombic unit cell so that gives a density (from the above calcs for metallic astatine) of 278.96 x 10^(–23) grams/412.3276 cubic Å = 6.76 grams per cubic centimetre, noting it is likely to be less than this given stronger intralayer bonding. For comparison, the figure cited in the article is 6.35 ±0.15. Sandbh (talk) 03:16, 17 April 2015‎ (UTC)

More recent papers on At chemistry

One, two, three, four, five. Double sharp (talk) 22:01, 12 November 2022 (UTC)

8 hour half-life vs immediately vaporized

@R8R, Sandbh, and Double sharp: To a layman, these two statements appear to conflict. We say a sample has never been assembled, with vaporization as an explanation, but then we would still have a gaseous sample. Or if by vaporization we mean more than just turn into a gas, then do we mean accelerate the half-life decay?

Onceinawhile (talk) 10:18, 16 September 2023 (UTC)

@Onceinawhile: Once the sample is vaporised, it's been disassembled. Double sharp (talk) 10:20, 16 September 2023 (UTC)

How is that different to being a gas? A sample of Helium is disassembled too. Onceinawhile (talk) 10:23, 16 September 2023 (UTC)

@Onceinawhile: Okay, fair enough. The way I'd think of it in the hypothetical situation (which is probably more or less what the article was going for), you'd have an astatine sample somewhere, and it would vaporise and diffuse through the air (thus disassembling itself) and cause a massive contamination problem. But I suppose we could think about it being done in a vacuum. So, to avoid doubts about the wording, I've changed it to Consequently, a solid sample of the element has never been seen, because any macroscopic specimen would be immediately vaporized by the heat of its radioactivity. Double sharp (talk) 10:28, 16 September 2023 (UTC)

I agree it's important to clarify text so that it is readily understood by all readers. Polyamorph (talk) 10:32, 16 September 2023 (UTC)

(edit conflict) I don't see the conflict. Research is limited because samples are not stable due to its short half-life and radioactive heating. With cooling techniques it might be possible to synthesise in weighable quantities but this is technically challenging. Sure you will obtain a gas, but then there are technical challenges of containing it safely and it will decay rapidly. Polyamorph (talk) 10:28, 16 September 2023 (UTC)

Thank you Double sharp and Polyamorph. It is a great article. It is a pleasure to read the details of those mysterious elements at the bottom of the periodic table that I would wonder about as a child. Onceinawhile (talk) 10:35, 16 September 2023 (UTC)

So the element has a half-life of about 8 hours, and when its atoms decay, they release a lot of energy. The energy is enough to break the bonds holding the atoms together in a solid state, vaporizing them into a gas. The atoms of astatine still exist as a vapor and are still decaying with a half-life of 8 hours. Just the phase of matter has changed. 108.160.120.91 (talk) 18:52, 16 September 2023 (UTC)

Yes, that is correct. Polyamorph (talk) 19:43, 16 September 2023 (UTC)

The shortest-lived element that anyone has seen as a macroscopic solid sample of seems to be radon (half-life 3.82 days). It was seen in 1909 when Gray and Ramsay measured its melting point: they wrote the solid glows with great brilliancy, like a small, steel-blue arc-light. (For obvious reasons I don't think anyone will be eager to repeat this experiment. That seems to have been at least 600 curies of radon, per 10.1002/anie.201803353. And no, that's not a typo for a less terrifying submultiple of a curie.) Double sharp (talk) 15:36, 17 September 2023 (UTC)

Interesting! Gray lived to his 80s, so didnt seem to do him any harm. Ramsey died age 63 of Nasal cancer, which may or may not be related to his radon work. Polyamorph (talk) 19:53, 18 September 2023 (UTC)

Melting and boiling points

What happened to the melting and boiling points of astatine? Did someone get rid of them? 2603:6000:8740:54B1:58F5:9310:2876:DD6 (talk) 13:36, 7 October 2023 (UTC)

There are no experimentally determined values for them. Various predicted values have been published, but there are too many to list exhaustively and there's no reason to favor one source over another; thus they are not included in the article ^Complex/_Rational 20:03, 7 October 2023 (UTC)

The other thing is that most of the values in the literature are predictions for At₂, and we don't know if condensed astatine is actually going to be diatomic. Double sharp (talk) 08:44, 11 October 2023 (UTC)

Density of fcc metallic At (conjectures)

1. Iodine at 53 GPa adopts a metallic FCC structure, with a volume (Å/atom) of 19.91 (doi:10.1103/physrevb.49.3725, p. 3727). Such a stucture has a packing efficiency of 74%.

The volume of one mole of such iodine atoms is 19.91 x 10^–24 x 6.022 x 10²³ = 11.99 cc.

Since the atomic weight of iodine is 126.9 this suggests a density of 0.74 x 126.9/11.99 = 7.83 gm/cc, compared to 4.93 gm/cc for ordinary iodine. Thus, the density from orthorhombic to fcc iodine increases 1.58 times.

If this occurs for fcc astatine, it suggests a density of 6.2–6.5 x 1.58 = 10.03±0.24 gm/cc. The figure of 6.2–6.5 is from doi:10.1021/j150609a021, pp. 1182, 1185).

2. Another way to look at this is the metallization collapse that occurs when R/V = 1. Here, R = molar refractivity and V = molar volume. Pauling pointed out that the cube root of molar refractivity is tantamount to an approximate measure of the radius of the outermost valence electrons in the atom. The orbital radius of At is 114.6 pm. Cubed, this yields an R value value of 15.05 cc which is ≈ to V. The density is then the atomic weight of At = 210 divided by the molar volume of 11.137 cc = 13.96 x 0.74 packing efficiency = 10.33 gm/cc.

3. "From the known atomic or molecular dipole polarizabilities, we can estimate the atomic densities required to form metallic solids as a consequence of an emerging polarization catastrophe. As these polarizabilities increase monotonically proceeding down the halogen group, the estimated compressions necessary for metallization decrease monotonically" (doi:10.1103/PhysRevLett.111.116404, p. 2). The polarizability for I is 32.9± atomic units and that for At is 42.2±4. On this basis the density of At is 42.2/32.9 x 7.83 (fcc I density) = 10.04 gm/cc. --- Sandbh (talk) 06:32, 13 January 2024 (UTC)

At high pressure, wouldn't the interatomic distance be smaller because of volume compression? So I guess hypothetical fcc iodine density at standard pressure (if that state could persist) would be somewhat lower than 7.83 (not sure how much). But these are conjectural anyway. Double sharp (talk) 07:43, 14 January 2024 (UTC)

From Arblaster (2018 p. 604):

"Hermann et al. 2013 have indicated that the correct room temperature structure is the metallic form and is probably face-centered cubic (cF4) with an estimated lattice parameter of 0.539 nm (Hermann 2014) which leads to the estimated crytallographic properties given in Table 85. The molar volume is notably lower than the range of 33.9 to 34.5 cm² mol^–1 estimated by Bonchev and Kamenska 1981 using the technique of information indices."

They give a density of 8.91 gm/cc for At-210, and 8.95 for At-211. The molar volume is 23.6 cc/mol. --- Sandbh (talk) 02:09, 24 January 2024 (UTC)

• Arblaster JW (ed.) 2018, Selected Values of the Crystallographic Properties of Elements, ASM International, Materials Park, Ohio
• Hermann A 2014, Priv.Comm., 10 January

--- Sandbh (talk) 02:09, 24 January 2024 (UTC)