Osmium is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element, with a density of 22.59 g/cm3. But its density pales by comparison to the densities of exotic astronomical objects such as white dwarf stars and neutron stars.
Protons and Neutrons in Osmium
Osmium is a chemical element with atomic number 76 which means there are 76 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 Osmium are 187-190, 192.
Main Isotopes of Osmium
Osmium occurs in 7 natural isotopes: 184Os, 186Os, 187Os, 188Os, 189Os, 190Os and 192Os. 186Os is very slightly radioactive, decaying by alpha decay with a half-life of 2.0×1015 years. 192Os is the most common isotope, having a natural abundance of approximately 40%.
Osmium-184 is composed of 76 protons, 108 neutrons, and 76 electrons.
Osmium-186 is composed of 76 protons, 110 neutrons, and 76 electrons.
Osmium-187 is composed of 76 protons, 111 neutrons, and 76 electrons.
Osmium-188 is composed of 76 protons, 112 neutrons, and 76 electrons.
Osmium-189 is composed of 76 protons, 113 neutrons, and 76 electrons.
Osmium-190 is composed of 76 protons, 114 neutrons, and 76 electrons.
Osmium-192 is composed of 76 protons, 116 neutrons, and 76 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 Osmium is 76. 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 Osmium is [Xe] 4f14 5d6 6s2.
Possible oxidation states are +3,4.
Most Common Compound of Osmium
Osmium forms compounds with oxidation states ranging from −2 to +8. The most common oxidation states are +2, +3, +4, and +8. The +8 oxidation state is notable for being the highest attained by any chemical element aside from iridium’s +9 and is encountered only in xenon, ruthenium, hassium and iridium. The most common compound exhibiting the +8 oxidation state is osmium tetroxide. This toxic compound is formed when powdered osmium is exposed to air. It is a very volatile, water-soluble, pale yellow, crystalline solid with a strong smell.
|Number of protons||76|
|Number of neutrons (typical isotopes)||187-190, 192|
|Number of electrons||76|
|Electron configuration||[Xe] 4f14 5d6 6s2|
Properties of other elements