85At

Astatine

Metalloidsolidblock p

The rarest naturally occurring element, with perhaps a single gram present in the whole Earth's crust at any moment, so it is made by cyclotron.

Atomic number	85
Mass number (longest-lived isotope)	210 g/mol
This element has no stable isotope, so it has no standard atomic weight. The figure above is the mass number of its longest-lived isotope — a convention, not a measurement of a natural mixture.
Group · period	17 · 6
Electron configuration	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵

About Astatine

Astatine exists in nature only as a fleeting step in uranium and thorium decay chains, and the entire crustal inventory at any instant is estimated at under 30 grams; its longest-lived isotope lasts 8.1 hours. Nobody has ever seen a bulk sample and nobody ever will, because the radioactive heating from any visible quantity would vaporise it instantly. Everything known about its chemistry comes from tracer work at concentrations below 10⁻¹¹ mol/L, which is why its classification is genuinely unsettled: it sits under the halogens, but calculations and recent condensed-phase measurements suggest metallic astatine would be a metal, not a diatomic non-metal. It is kept as a metalloid here on that basis. Astatine-211 is under active trial as a targeted alpha-emitting cancer therapy.

Use 210 g/mol in these solvers

Moles from Mass (n = m/M)

n = \frac{m}{M}

Opens with M = 210 g/mol already filled in

Gas Density from Molar Mass

\rho = \frac{PM}{RT}

Opens with M = 210 g/mol already filled in

Faraday's Law of Electrolysis (m = QM/nF)

m = \frac{Q M}{n F}

Opens with M = 210 g/mol already filled in

Ion Concentration as CaCO₃ Equivalent

C_{\mathrm{CaCO_3}} = C_{\mathrm{ion}} \times \frac{50.04}{\mathrm{EW}}

Opens with EW = 210 g/mol already filled in

Acid Feed to Reduce Alkalinity

\dot m = \frac{\Delta \mathrm{Alk} \, Q \times \frac{\mathrm{EW}}{50.04}}{p/100\%}

Opens with EW = 210 g/mol already filled in

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