Hund's rule of maximum multiplicity, often simply referred to as Hund's rule, is a principle of atomic chemistry which states that a greater total spin state usually makes the resulting atom more stable, most commonly manifested in a lower energy state, because it forces the unpaired electrons to reside in different spatial orbitals. A commonly given reason for the increased stability of high multiplicity states is that the different occupied spatial orbitals create a larger average distance between electrons, reducing electron-electron repulsion energy. In reality, it has been shown that the actual reason behind the increased stability is a decrease in the screening of electron-nuclear attractions,. Total spin state is calculated as the total number of unpaired electrons + 1, or twice the total spin + 1 written as 2s+1. Multicolored chemicals are frequent hallmarks of chemistry. ... The word stability has a number of technical meanings, all related to the common meaning of the word. ... An energy level is a quantified stable energy, which a physical system can have; the term is most commonly used in reference to the electron configuration of electrons, in atoms or molecules. ...

Friedrich Hund discovered this rule and others referred to collectively as Hund's rules for atomic energy levels. They are important for spectroscopy and quantum chemistry. ... In atomic physics, Hunds rules, discovered by Friedrich Hund, determine which is the term symbol that corresponds to the ground state of a multi-electron atom. ... Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines) Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ... Linus Pauling, as a pioneer of the valence bond theory, is one of the first quantum chemists. ...

As a result of Hund's rule of Maximum multiplicity, constraints are placed on the way atomic orbitals are filled using the Aufbau principle. Before any two electrons occupy an orbital in a subshell, other orbitals in the same subshell must first each contain one electron. Also, the electrons filling a subshell will have parallel spin before the shell starts filling up with the opposite spin electrons (after the first orbital gains a second electron). As a result, when filling up atomic orbitals, the maximum number of unpaired electrons (and hence maximum total spin state) is assured. The Aufbau principle (also Aufbau rule or building-up principle), is used to determine the electron configuration of an atom, molecule or ion. ... 2 (two) is the natural number following 1 and preceding 3. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... It has been suggested that Energy level be merged into this article or section. ... In atomic physics, an electron subshell is a group of atomic orbitals with the same values of the principal quantum number n and the angular momentum quantum number l. ...

In 2004, it was reported in PhysicsWeb that researchers had synthesized 5-dehydro-m-xylylene (DMX), the first organic molecule known to violate Hund's rule. ^[1]. The journal article reporting the discovery is in Angewante Chemie (L Slipchenko et al. Angew. Chem. Int. Ed. 2004 43 742) It has been designated the: International Year of Rice (by the United Nations) International Year to Commemorate the Struggle against Slavery and its Abolition (by UNESCO) 2004 World Health Day topic was Road Safety (by World Health Organization) Year of the Monkey (by the Chinese calendar) See the world in... PhysicsWeb is a web site providing various up-to-date information relating to the study and application of physics. ... 5-dehydro-m-xylylene, or DMX is an organic triradical molecule which violates Hunds Rule. ... An organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with the exception of carbides, carbonates, carbon oxides and gases containing carbon. ... In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ...

External links

• A glossary entry hosted on the web site of the Chemistry Department of Purdue University

References

1. ↑  2004, Radical molecule breaks the rules, Physics Web, retrieved December 21, 2005.