Protactinium
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.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
86 is the [Rn] core total across six shells.
At a glance
- Atomic number
- 91
- Atomic mass
- 231.035882 u
- Phase
- Solid
- Density
- 15.37 g/cm³
- Melting point
- 1,841 K
- Boiling point
- 4,300 K
- First ionization energy
- 568 kJ/mol
- Electronegativity
- 1.5
- Electron affinity
- 53.03 kJ/mol
- Molar heat capacity
- Unavailable
- Period
- 7
- Appearance
- bright, silvery metallic luster
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.