Symbol	Pa
Atomic number	91
Group	-
Period	7
Block	f
Classification	Actinide

Appearance	Bright, silvery metallic luster
Color	Silver

Number of protons	91 p+
Number of neutrons	140 n0
Number of electrons	91 e-

From Wikipedia, the free encyclopediaProtactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states.

Phase at STP	Solid
Density	15.37 g/cm3
Atomic weight	231.036 u

Melting point	1841 K 1567.85 °C 2854.13 °F
Boiling point	4300 K 4026.85 °C 7280.33 °F
Heat of vaporization	481.2 kJ/mol

Electronegativity (Pauling Scale)	1.5
Electron affinity	53.03 kJ/mol
Oxidation states	+2, +3, +4, +5 (a weakly basic oxide)
Ionization energies	568 kJ/mol 1128 kJ/mol 1814 kJ/mol 2991 kJ/mol

Electron configuration Shorthand configuration	[Rn] 5f2 6d1 7s2
Electron configuration Full configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f2 6s2 6p6 6d1 7s2
Electron configuration chart	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f2 6s2 6p6 6d1 7s2
Electrons per shell	2, 8, 18, 32, 20, 9, 2
Valence electrons	2
Valency electrons	2,3,4,5
Bohr model	Figure: Shell diagram of Protactinium (Pa) atom.
Orbital Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 7s

Prediction	Dmitri Mendeleev
Discovery	Oswald Helmuth Göhring, Kazimierz Fajans (1913)
Named by	Otto Hahn, Lise Meitner (1917)

CAS Number	7440-13-3
ChemSpider ID	22387
EC number	616-087-9
PubChem CID Number	23945