Thorium

ACTINIDE

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

Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only two significantly radioactive elements that still occur naturally in large quantities as a primordial element (the other being uranium). It was discovered in 1828 by the Norwegian Reverend and amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius, who named it after Thor, the Norse god of thunder.

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Quick Facts

Atomic Number 90

Period 7

Group 4

Phase Solid

Appearance silvery, often with black tarnish

About Actinides

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

History

Discovered By Jöns Jakob Berzelius

Named By Unknown

Physical Properties

Atomic Mass 232.03774

Density 11.724 g/L

Molar Heat 26.23 J/(mol·K)

Phase Transition (Melting & Boiling Points)

Thorium melts at 2023 K and boils at 5061 K.

Atomic Properties

Electron Config [Rn] 6d2 7s2

Electronegativity 1.3

Electron Affinity 112.72 kJ/mol

Ionization Energy 587 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

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.