Uranium is a silvery-white metal in the actinide series of the periodic table. Uranium is weakly radioactive because all isotopes of uranium are unstable, with half-lives varying between 159,200 years and 4.5 billion years. Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead, and slightly lower than that of gold or tungsten. Uranium is commonly found at low levels (a few ppm – parts per million) in all rocks, soil, water, plants, and animals (including humans). Uranium occurs also in seawater, and can be recovered from the ocean water. Significant concentrations of uranium occur in some substances such as uraninite (the most common uranium ore), phosphate rock deposits, and other minerals.
Protons and Neutrons in Uranium
Uranium is a chemical element with atomic number 92 which means there are 92 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 Uranium are 238, 235.
Main Isotopes of Uranium
Uranium occurs in 5 natural isotopes: 233U, 234U, 235U, 236U and 238U. All isotopes are very slightly radioactive. 238U is the most common isotope, having a natural abundance of approximately 99%. Other isotopes occur only in traces.
Uranium-233 is composed of 92 protons, 141 neutrons, and 92 electrons.
Uranium-234 is composed of 92 protons, 142 neutrons, and 92 electrons.
Uranium-235 is composed of 92 protons, 143 neutrons, and 92 electrons.
Uranium-236 is composed of 92 protons, 144 neutrons, and 92 electrons.
Uranium-238 is composed of 92 protons, 146 neutrons, and 92 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 Uranium is 92. 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 Uranium is [Rn] 5f3 6d1 7s2.
Possible oxidation states are +3,4,5,6.
Most Common Compound of Uranium
Uranium dioxide is a ceramic refractory uranium compound, in many cases used as a nuclear fuel. Most of LWRs use the uranium fuel, which is in the form of uranium dioxide (chemically UO2). Uranium dioxide is a black semiconducting solid with very low thermal conductivity. On the other hand the uranium dioxide has a very high melting point and has well known behavior.
|Number of protons||92|
|Number of neutrons (typical isotopes)||238, 235|
|Number of electrons||92|
|Electron configuration||[Rn] 5f3 6d1 7s2|
Properties of other elements