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91 Pa Protactinium 231.035882

Protactinium

ACTINIDE
Bohr Model: Electrons arranged in energy shells around the nucleus.

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.

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Quick Facts

Atomic Number 91
Period 7
Group 5
Phase Solid
Appearance bright, silvery metallic luster
About Actinides

Actinides are the 15 metallic elements with atomic numbers 89–103. All actinides are radioactive.

History

Discovered By William Crookes
Named By Otto Hahn

Physical Properties

Atomic Mass 231.035882
Density 15.37 g/L
Molar Heat N/A J/(mol·K)
Phase Transition (Melting & Boiling Points)

Protactinium melts at 1841 K and boils at 4300 K.

Atomic Properties

Electron Config [Rn] 5f2 6d1 7s2
Electronegativity 1.5
Electron Affinity 53.03 kJ/mol
Ionization Energy 568 kJ/mol
Orbital Filling Diagram
This diagram visualizes electron configuration according to the Aufbau principle and Hund's rule. Boxes represent orbitals (s, p, d, f), while arrows indicate electrons with spin up or down. Electrons fill lower energy levels first and occupy orbitals singly before pairing.

Photograph

Image of Protactinium Source: Wikipedia

External Resources

Wikipedia PubChem Royal Society of Chemistry Periodic Videos (YouTube)

Study Guide

Atomic Number

The number of protons in the nucleus, which defines the element.

Atomic Mass

The average mass of an atom, including protons and neutrons.

Electronegativity

A measure of how strongly an atom attracts electrons in a bond.

Ionization Energy

The energy required to remove an electron from an atom.

Electron Config

The arrangement of electrons in the atom's energy shells.