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This article is about an undiscovered element. Once it is discovered, this article will be edited with more information.

Unseptunium is a hypothetical superheavy halogen with the symbol Usu and atomic number 171. If it exists, it will be the second last one of the ninth period.

Period 9 elements
9 165
Uhp
166
Uhh
167
Uhs
168
Uho
169
Uhe
170
Usn
171
Usu
172
Usb
Alkali metal Alkaline earth metal Lanthanide Actinide Superactinide Eka-superactinide Transition metal Post-transition metal Metalloid Other nonmetal Halogen Noble gas
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