Atomic Number
91
Element 91
Protactinium (Pa)
Protactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids.
Atomic Mass
231.04 u
Category
Actinide
Period
7
Group
Actinide series
Phase
solid
Density
15.37 g/cm3
Electron Shells
2, 8, 18, 32, 20, 9, 2
Atomic Structure
Protons: 91. Electrons: 91. Neutrons: Varies by isotope.
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f² 6d¹
Why Protactinium Matters
Protactinium helps connect atomic number 91, actinide behavior, period 7 trends, and electron shell structure. Its solid phase, atomic mass of 231.04 u, and electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f² 6d¹ make it useful for comparing bonding patterns across the periodic table.
Discovery and Occurrence
Protactinium was discovered 1917 by Lise Meitner, Otto Hahn. Protactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids.
Safety and Handling Context
Protactinium has radioactive isotopes or is commonly discussed with radioactive materials. Use this page as an educational reference; real samples require qualified supervision and controlled handling.
Related Elements
Frequently Asked Questions
- What is the atomic number of Protactinium?
- Protactinium has atomic number 91, which means a neutral atom has 91 protons and 91 electrons.
- What is the chemical symbol for Protactinium?
- The chemical symbol for Protactinium is Pa.
- What category is Protactinium in?
- Protactinium is classified as a actinide and sits in period 7 of the periodic table.
Explore Protactinium in 3D
Use the interactive table above to rotate atomic models, compare periodic trends, and move from Protactinium to neighboring elements without losing your place.