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The Element Thorium


"The Atom"

Definition of the Thorium Element
A radioactive metallic element that occurs combined in minerals and is usually associated with rare earths. When pure, thorium is a silvery white metal which is air-stable and retains its lustre for several months. When heated in air, thorium turnings ignite and burn brilliantly with a white light. Thorium is used as an alloying element in Magnesium, to coat Tungsten wire and in the manufacture of refractory materials for the metallurgical industries. The Atomic Number of this element is 90 and the Element Symbol is Th.

The Properties of the Thorium Element
Symbol of Element : Th
Atomic Number : 90
Atomic Mass: 232.0381 amu
Melting Point: 1750.0 C - 2023.15 K
Boiling Point: 4790.0 C - 5063.15 K
Number of Protons/Electrons: 90
Number of Neutrons : 142
Crystal Structure: Cubic
Density @ 293 K: 11.72 g/cm3
Color of Thorium : silvery

Origin / Meaning of the name Thorium
Thorium was named after Thor, the Norse God of War.

Periodic Table Group and Classification of the of the Thorium Element
Elements can be classified based on their physical states (States of Matter) e.g. gas, solid or liquid. This element is a solid. Thorium is classified as an element in the Actinide series as one of the "Rare Earth Elements" which can located in Group 3 elements of the Periodic Table and in the 6th and 7th periods. The Rare Earth Elements are of the Lanthanide and Actinide series. Most of the elements in the Actinide series are synthetic or man-made. Nearly 75% of all the elements in the Periodic Table are classified as metals which are detailed in the List of Metals.

Facts about the Discovery and History of the Thorium Element
Thorium was discovered by Jons Jacob Berzelius  in Sweden in 1828.

History of the Periodic Table
Check out the brief History of the Periodic Table which details dates and the names of famous scientists and chemists who contributed to the development of the Periodic Table.

Occurrence of the Thorium Element
Monazite is the primary source of thorium

Abundances of the element in different environments
% in Universe 410-8%
% in Sun 310-8%
% in Meteorites 3.910-6%
% in Earth's Crust 0.0006%
% in Oceans 410-12%
% in Humans None

Associated Uses of Thorium
Nuclear fuel
Uranium and thorium has been used to date hominid fossils.

Site Index
Rare Earth Elements
Atomic Number
Element Symbol
Periodic Table

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