Selenium is a nonmetal with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth’s crust.
Protons and Neutrons in Selenium
Selenium is a chemical element with atomic number 34 which means there are 34 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 Selenium are 74; 76; 77; 78; 80.
Main Isotopes of Selenium
Selenium occurs in 5 natural isotopes: 74Se, 76Se, 77Se, 78Se, 79Se, 80Se and 82Se. Of these, 79Se is a trace radioisotope, decaying by beta decay with a half-life of 3.27×105 years. 82Se is decaying by double beta decay with a half-life of 1.08×1020 years. 80Se is the most common isotope, having a natural abundance of approximately 49.8%.
Selenium-74 is composed of 34 protons, 40 neutrons, and 34 electrons.
Selenium-76 is composed of 34 protons, 42 neutrons, and 34 electrons.
Selenium-77 is composed of 34 protons, 43 neutrons, and 34 electrons.
Selenium-78 is composed of 34 protons, 44 neutrons, and 34 electrons.
Selenium-79 is composed of 34 protons, 45 neutrons, and 34 electrons.
Selenium-80 is composed of 34 protons, 46 neutrons, and 34 electrons.
Selenium-82 is composed of 34 protons, 48 neutrons, and 34 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 Selenium is 34. 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 Selenium is [Ar] 3d10 4s2 4p4.
Possible oxidation states are +4,6/-2.
Most Common Application of Selenium
The chief commercial uses for selenium today are glassmaking and pigments. Selenium finds applications in the various industries, for example, solar cells and photoconductor applications.
|Number of protons||34|
|Number of neutrons (typical isotopes)||74; 76; 77; 78; 80|
|Number of electrons||34|
|Electron configuration||[Ar] 3d10 4s2 4p4|
Properties of other elements