thorium - protactinium - uranium Pr Pa Full table
General
Name, Symbol, Number	protactinium, Pa, 91
Chemical series	Transition metals
Group, Period, Block	_ , 7, f
Density, Hardness	15370 kg/m3, no data
Appearance	bright, silvery metallic luster
Atomic properties
Atomic weight	231.03588(2) amu
Atomic radius (calc.)	180 (no data) pm
Covalent radius	no data
van der Waals radius	no data
Electron configuration	[Rn]7s²5f²6d¹
e- 's per energy level	2, 8, 18, 32, 20, 9, 2
Oxidation states (Oxide)	5 (weak base)
Crystal structure	orthorhombic
Physical properties
State of matter	solid
Melting point	2113 K (2912 °F)
Boiling point	4300 K (7281 °F)
Molar volume	15.18 ×10-3 m3/mol
Heat of vaporization	470 kJ/mol
Heat of fusion	15 kJ/mol
Vapor pressure	5.1E-5 Pa at 2200 K
Velocity of sound	no data
Miscellaneous
Electronegativity	1.5 (Pauling scale)
Specific heat capacity	120 J/(kg*K)
Electrical conductivity	5.29 106/m ohm
Thermal conductivity	47 W/(m*K)
1st ionization potential	568 kJ/mol
2nd ionization potential	no data
3rd ionization potential	no data
4th ionization potential	no data
Most stable isotopes
iso NA half-life DM DE MeV DP 230Pa {syn.} 17.4 d ε 1.310 230Th β- 0.563 230U 231Pa {syn.} 32760 a α 5.149 227Ac 233Pa {syn.} 26.967 d β- 0.571 233U
SI units & STP are used except where noted.

Protactinium is a chemical element in the periodic table that has the symbol Pa and atomic number 91.

Notable Characteristics

Protactinium is a silver metallic element that belongs to the actinide group, with a bright metallic luster that it retains for some time in the air. It is superconductive at temperatures below 1.4 K.

Applications

Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic scientific research.

History

Protactinium was first identified in 1913, when Kasimir Fajans and O. H. Göhring encountered short-lived isotope 234m-Pa, with a half-life of about 1.17 minutes, during their studies of the decay chain of 238-U. They gave the new element the name Brevium (Latin brevis, brief, short); the name was changed to Protoactinium in 1918 when two groups of scientists (Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of the UK) independently discovered 231-Pa, and shortened to Protactinium in 1949.

Aristid V. Grosse prepared 2 mg of Pa₂O₅ in 1927, and later on managed to isolate Protactinium for the first time in 1934 from 0.1 mg of Pa₂O₅, first converting the oxide to an iodide and then cracking it in a high vacuum by an electrically heated filament by the reaction 2PaI₅ → 2Pa + 5I₂.

In 1961, the United Kingdom Atomic Energy Authority was able to produce 125 g of 99.9% pure protactinium, processing 60 tons of waste material in a 12-stage process and spending 500,000 USD; this was the world's only supply of the element for many years to come, and it is reported that the metal was sold to laboratories for a cost of 2,800 USD / g in the following years.

Biological Role

Protactinium does not play any biological role.

Occurrence

Protactinium occurs in pitchblende to the extent of about 1 part 231-Pa to 10 million of ore; ores from Zaire have about 3 ppm.

Compounds

Known protactinium compounds include:

• Fluorides
  • PaF₄
  • PaF₅
• Chlorides
  • PaCl₄
  • PaCl₅
• Bromides
  • PaBr₄
  • PaBr₅
• Iodides
  • PaI₃
  • PaI₄
  • PaI₅
• Oxides
  • PaO
  • PaO₂
  • Pa₂O₅

Isotopes

29 radioisotopes of protactinium have been characterized, with the most stable being 231-Pa with a half life of 32760 years, 233-Pa with a half-life of 26.967 days, and 230-Pa with a half-life of 17.4 days. All of the remaining radioactive isotopes have half-lifes that are less than 1.6 days, and the majority of these have half lifes that are less than 1.8 seconds. This element also has 2 meta states, 217m-Pa (t_½ 1.15 milliseconds) and 234m-Pa (t_½ 1.7 minutes).

The primary decay mode before the most stable isotope, 231-Pa, is alpha decay and the primary mode after is beta minus decay. The primary decay products before 231-Pa are element Ac (actinium) isotopes and the primary products after are element U (uranium) isotopes.

Precautions

Protactinium is both toxic and highly radioactive; it requires precautions similar to those used when handling plutonium.

External links

• WebElements.com - Protactinium
• EnvironmentalChemistry.com - Protactinium
• It's Elemental - Protactinium
• InfoHaunter [1]