Protactinium

Protactinum, ₉₁Pa

Protactinum
Pronunciation	/ˌproʊtækˈtɪniəm/ ​(PROH-tak-TIN-ee-əm)
Standard atomic weight Ar, std(Pa)	7002231035880000000♠231.03588(1)
Protactinum in the periodic cairt
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gowd Mercur (element) Thallium Leid (element) Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium Pr ↑ Pa ↓ Uqp thorium ← Protactinum → uranium
Atomic nummer (Z)	91
Group	group n/a
Period	period 7
Block	f-block
Element category	Actinide
Electron confeeguration	[Rn] 5f2 6d1 7s2
Electrons per shell	2, 8, 18, 32, 20, 9, 2
Pheesical properties
Phase at STP	solid
Meltin pynt	1841 K ​(1568 °C, ​2854 °F)
Heat o fusion	12.34 kJ/mol
Heat o vapourisation	481 kJ/mol
Atomic properties
Oxidation states	+2, +3, +4, +5 waikly basic
Ionisation energies	1st: 586 kJ/mol
Atomic radius	empirical: 163 pm
Colour lines in a spectral range Spectral lines o Protactinum
Ither properties
Thermal expansion	~9.9 µm/(m·K)
Thermal conductivity	47 W/(m·K)
Electrical resistivity	177 Ω·m
CAS Nummer	7440-13-3
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct

Protactinium is a chemical element in the periodic cairt that haes the seembol Pa, atomic nummer 91, an atomic mass 231.036. It is a siller-coloured metal an ane o the actinides. It readily reacts wi oxygen, watter vapor an inorganic acids. It forms sindry chemical compoonds whaur protactinium is uisually wi in the oxidation state +5, but it can assume +4 an e'en +3 or +2 states an aw. Concentrations o protactinium in the Yird's crust are teepically twa-three pairts ilka trillion, but micht rax tae twa-three pairts ilka million in some uraninite ore deposits. Acause o its scarcity, heich radioactivity an heich toxicity, thare arenae ony uises for protactinium ootwi scientific resairch the nou, an for this purpose, protactinium is maistly taen frae spent nuclear fuel.

The element wis first fund in 1913 bi Kazimierz Fajans an Oswald Helmuth Göhring an cried "brevium" acause o the short hauf-life o the speceefic isotope studied, i.e. protactinium-234m. A mair stable isotope o protactinium, ²³¹Pa, wis diskivert in 1917/18 bi Lise Meitner in collaboration wi Otto Hahn, an thay chose the name protactinium. The IUPAC chose the name "protactinium" in 1949 an confirmt Hahn an Meitner as diskiverers. The new name meant "(nuclear) precursor tae actinium", an implied thit actinium is a product o radioactive decay o protactinium. John Arnold Cranston (working wi Frederick Soddy an Ada Hitchins) is credited wi diskiverin the maist stable isotope in 1915 an aw, but pit back his annooncement due tae bein cawed up for sairvice in the First Warld War.