Promethium is one of only two such elements that are followed in the periodic table by elements with stable forms. All of its isotopes are radioactive. In nuclear reactors, promethium equilibrium exists in power operation. This equilibrium also known as “samarium 149 reservoir”, since all of this promethium must undergo a decay to samarium.
Protons and Neutrons in Promethium
Promethium is a chemical element with atomic number 61 which means there are 61 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 Promethium are 149.
Main Isotopes of Promethium
Promethium occurs in 2 natural isotopes: 145Pm and 147Pm. Both occur only in traces.
Promethium-145 is composed of 61 protons, 84 neutrons, and 61 electrons.
Promethium-147 is composed of 61 protons, 85 neutrons, and 61 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 Promethium is 61. 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 Promethium is [Xe] 4f5 6s2.
Possible oxidation states are +3.
Most Common Compounds of Promethium
Promethium belongs to the cerium group of lanthanides and is chemically very similar to the neighboring elements. Because of its instability, chemical studies of promethium are incomplete. Promethium is not extensively used metal. Most promethium is used only in research. Even though a few compounds have been synthesized, they are not fully studied; in general, they tend to be pink or red in color.
|Number of protons
|Number of neutrons (typical isotopes)
|Number of electrons
|[Xe] 4f5 6s2