Protactinium
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Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. I
Sample of protactinium-231 in a glass vial
Dmitri Mendeleev's 1871 periodic table with a gap for protactinium on the bottom row of the chart, between thorium and uranium
Protactinium occurs in uraninite ores.
Periodic table
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The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows and columns. An icon of chemistry, the periodic table is widely used
Protactinium
…below zirconium in group IV, leaving the space below tantalum in group V empty. Until the general acceptance of the actinide concept in the late 1940s, periodic tables were published with this structure. For a long time, chemists searched for eka-tantalum as an element with similar chemical properties to tantalum…
Liquid mercury. Its liquid state at standard conditions is the result of relativistic effects.
Graphite and diamond, two allotropes of carbon
Iron, a metal
Sulfur, a nonmetal