Thorium metal is silvery and tarnishes black when exposed to air, forming the dioxide. Thorium is moderately hard, malleable, and has a high melting point. Thorium is a naturally-occurring element and it is estimated to be about three times more abundant than uranium. Thorium is commonly found in monazite sands (rare earth metals containing phosphate mineral).
Protons and Neutrons in Thorium
Thorium is a chemical element with atomic number 90 which means there are 90 protons in its nucleus. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10-19 coulombs.
The total number of neutrons in the nucleus of an atom is called the neutron number of the atom and is given the symbol N. Neutron number plus atomic number equals atomic mass number: N+Z=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N – Z = A – 2Z.
For stable elements, there is usually a variety of stable isotopes. Isotopes are nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons. Mass numbers of typical isotopes of Thorium are 232.
Main Isotopes of Thorium
Thorium occurs in 7 natural isotopes: 227Th, 228Th, 229Th, 230Th, 231Th, 232Th and 234Th. All isotopes are very slightly radioactive. 232Th is the most common isotope, having a natural abundance of approximately 99%. Other isotopes occur only in traces.
Thorium-227 is composed of 90 protons, 137 neutrons, and 90 electrons.
Thorium-228 is composed of 90 protons, 138 neutrons, and 90 electrons.
Thorium-229 is composed of 90 protons, 139 neutrons, and 90 electrons.
Thorium-230 is composed of 90 protons, 140 neutrons, and 90 electrons.
Thorium-231 is composed of 90 protons, 141 neutrons, and 90 electrons.
Thorium-232 is composed of 90 protons, 142 neutrons, and 90 electrons.
Thorium-234 is composed of 90 protons, 144 neutrons, and 90 electrons.
Electrons and Electron Configuration
The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the number of electrons in neutral atom of Thorium is 90. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
Since the number of electrons and their arrangement are responsible for the chemical behavior of atoms, the atomic number identifies the various chemical elements. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Electron configuration of Thorium is [Rn] 6d2 7s2.
Possible oxidation states are +4.
Most Common Compound of Thorium
Most thorium applications use its dioxide (sometimes called “thoria” in the industry), rather than the metal. This compound has a melting point of 3300 °C (6000 °F), the highest of all known oxides; only a few substances have higher melting points.
|Number of protons||90|
|Number of neutrons (typical isotopes)||232|
|Number of electrons||90|
|Electron configuration||[Rn] 6d2 7s2|
Properties of other elements