In the context of atomic orbitals, an open shell is a valence shell which is not completely filled with electrons or that has not given all of its valence electrons through chemical bonds with other atoms or molecules during a chemical reaction. Atoms generally reach a noble gas configuration in a molecule. The Noble gases (He, Ne, Ar, Kr, Xe, Rn) are not reactive and have configurations 1s² (He), 1s²2s²2p⁶ (Ne), 1s²2s²2p⁶3s²3p⁶ (Ar), etc. An atomic orbital is the description of the behavior of an electron in an atom according to quantum mechanics. ... The valence shell is the outermost shell of an atom, which contains the electrons most likely to account for the nature of any reactions involving the atom and of the bonding interactions it has with other atoms. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... Properties For alternative meanings see atom (disambiguation). ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... This article is about the chemical series. ...

For molecules it signifies that there are unpaired electrons. In molecular orbital theory, this leads to molecular orbitals that are singly occupied. In computational chemistry implementations of molecular orbital theory, open shell molecules have to be handled by either the restricted Open-shell Hartree-Fock method or the unrestricted Hartree-Fock method. In chemistry, a molecular orbital is a region in which an electron may be found in a molecule. ... Computational chemistry is a branch of chemistry that uses the results of theoretical chemistry incorporated into efficient computer programs to calculate the structures and properties of molecules and solids, applying these programs to complement the information obtained by actual chemical experiments, predict hitherto unobserved chemical phenomena, and solve related problems. ... Restricted Open-shell Hartree-Fock (ROHF) is a variant of Hartree-Fock theory for open shell molecules. ... Unrestricted Hartree-Fock (UHF) theory is the most common molecular orbital method for open shell molecules where the number of electrons of each spin are not equal. ...

Likewise a closed shell or closed shell configuration is obtained with a completely filled valence shell. This configuration is very stable ^[1]. In another meaning a closed shell configuration corresponds to state with all molecular orbitals doubly occupied or empty (a singlet state) ^[2] In chemistry, a molecular orbital is a region in which an electron may be found in a molecule. ... Wikipedia does not have an article with this exact name. ...

See also

• Periodic table (electron configurations)
• Octet rule
• Valence shell
• Free radical

electron numbers indicate subshells that are filled to their maximum. ... The bonding in carbon dioxide (CO2): all atoms are surrounded by 8 electrons, according to the octet rule. ... The valence shell is the outermost shell of an atom, which contains the electrons most likely to account for the nature of any reactions involving the atom and of the bonding interactions it has with other atoms. ... In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ...

References

3. iOpenShell Center for computational studies of open-shell and electronically excited species