Protactinium is a chemical element with the symbol Pa, Atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds in which protactinium is usually present in the oxidation state +5, but it can also assume +4 and even +3 or +2 states.
It was discovered in 1917/18 by Otto Hahn and Lise Meitner, and they chose the name proto-actinium, but the IUPAC finally named it “protactinium” in 1949 and confirmed Hahn and Meitner as discoverers.
Physical and Chemical Properties of Protactinium
- It is a shiny, radioactive and silvery metal that degrades slowly in the presence of air to form oxides.
- It has around five isotopes with their mass numbers ranging between 212 to 238 and protactinium 231 is considered to be the most stable isotope with a half-life of about 32,760 years. This isotope is produced by the decay of element uranium 235 by emitting gamma radiation.
- It is an actinide which is positioned in the periodic table to the left of uranium and to the right of thorium, and many of its physical properties are intermediate between those two actinides.
- It is more dense and rigid than thorium but is lighter than uranium, and its melting point is lower than that of thorium and higher than that of uranium.
- The thermal expansion, electrical and thermal conductivity of these three elements are comparable and are typical of post-transition metals. The estimated shear modulus of protactinium is similar to that of titanium.
- It is a metal with silvery-gray luster that is preserved for some time in air. Protactinium easily reacts with oxygen, water vapor and acids, but not with alkalis.