Po Z84 [Xe]4f¹⁴5d¹⁰6s²6p⁴ 209.98 silvery rare → NEXT SHELL At Z85 [Xe]4f¹⁴5d¹⁰6s²6p⁵ 210 BLACK METALLIC HALOGEN — rarest natural — black metal analog — group 17 — p⁵ — χ 2.2 — melt 302°C boil 337°C est — black metallic luster — halogen → NEXT Rn Z86 full p⁶ closes P6
At — predicted face-centered cubic black metal — metallic under pressure — halogen that acts like metal — only 0.07g in entire Earth's crust at any moment — At-211 medical metal analog — At+ / At- metal analog pair