91 - Protactinium actinide
Discovered by William Crookes in 1917
Protactinium 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.
Periodic table
| Shell | Electrons | Orbitals |
|---|---|---|
| 1 | 2 | 2 in 1s |
| 2 | 8 | 2 in 2s + 6 in 2p |
| 3 | 18 | 2 in 3s + 6 in 3p + 10 in 3d |
| 4 | 32 | 2 in 4s + 6 in 4p + 10 in 4d + 14 in 4f |
| 5 | 20 | 2 in 5s + 6 in 5p + 10 in 5d + 2 in 5f |
| 6 | 9 | 2 in 6s + 6 in 6p + 1 in 6d |
| 7 | 2 | 2 in 7s |
Electron shells
bright, silvery metallic luster Appearance
231 u Atomic Mass
4.3k K Boiling Point
5 Group
5 Common Oxidation States
2 Å Covalent Radius
15.4 g/cm³ Density
53 kJ/mol Electron Affinity
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f2 6d1 Electron Configuration
[Rn] 5f2 6d1 7s2 Electron Configuration (semantic)
1.5 Electronegativity
91 Electrons
5.89 eV First Ionization Energy
568 kJ/mol Ionization Energies
1.87k K Melting Point
46 Mendeleev Number
7 Number of Shells
140 Neutrons
91 Atomic Number
14 Number of Isotopes
3, 4, 5 Oxidation States
7 Period
Solid Phase
91 Protons