Periodic table with elements that have unpaired electrons coloured
In chemistry, an unpaired electron is an electron that occupies an orbital of an atom singly, rather than as part of an electron pair. Each atomic orbital of an atom (specified by the three quantum numbers n, l and m) has a capacity to contain two electrons (electron pair) with opposite spins. As the formation of electron pairs is often energetically favourable, either in the form of a chemical bond or as a lone pair, unpaired electrons are relatively uncommon in chemistry, because an entity that carries an unpaired electron is usually rather reactive. In organic chemistry they typically only occur briefly during a reaction on an entity called a radical; however, they play an important role in explaining reaction pathways.
Radicals are uncommon in s- and p-block chemistry, since the unpaired electron occupies a valence p orbital or an sp, sp2 or sp3 hybrid orbital. These orbitals are strongly directional and therefore overlap to form strong covalent bonds, favouring dimerisation of radicals. Radicals can be stable if dimerisation would result in a weak bond or the unpaired electrons are stabilised by delocalisation. In contrast, radicals in d- and f-block chemistry are very common. The less directional, more diffuse d and f orbitals, in which unpaired electrons reside, overlap less effectively, form weaker bonds and thus dimerisation is generally disfavoured. These d and f orbitals also have comparatively smaller radial extension, disfavouring overlap to form dimers.[1]
Relatively more stable entities with unpaired electrons do exist, e.g. the nitric oxide molecule has one. According to Hund's rule, the spins of unpaired electrons are aligned parallel and this gives these molecules paramagnetic properties.
The most stable examples of unpaired electrons are found on the atoms and ions of lanthanides and actinides. The incomplete f-shell of these entities does not interact very strongly with the environment they are in and this prevents them from being paired. The ions with the largest number of unpaired electrons are Gd3+ and Cm3+ with seven unpaired electrons.
An unpaired electron has a magnetic dipole moment, while an electron pair has no dipole moment because the two electrons have opposite spins so their magnetic dipole fields are in opposite directions and cancel. Thus an atom with unpaired electrons acts as a magnetic dipole and interacts with a magnetic field. Only elements with unpaired electrons exhibit paramagnetism, ferromagnetism, and antiferromagnetism.
^N. C. Norman (1997). Periodicity and the s- and p-Block Elements. Oxford University Press. p. 43. ISBN 0-19-855961-5.
In chemistry, an unpairedelectron is an electron that occupies an orbital of an atom singly, rather than as part of an electron pair. Each atomic orbital...
Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpairedelectrons. The...
their spin, unpairedelectrons have a magnetic dipole moment and act like tiny magnets. An external magnetic field causes the electrons' spins to align...
one-electron reduction of dioxygen O2, which occurs widely in nature. Molecular oxygen (dioxygen) is a diradical containing two unpairedelectrons, and...
extended to molecules with an odd number of electrons by treating the unpairedelectron as a "half electron pair"—for example, Gillespie and Nyholm: 364–365 ...
angular momentum of the electrons contained in a compound. Compounds are diamagnetic when they contain no unpairedelectrons. Molecular compounds that...
strong tendency to pair off electrons can be observed in chemistry, it is also possible for electrons to occur as unpairedelectrons. In the case of metallic...
complexes and oxides. Most are strongly paramagnetic because of their unpaired d electrons, as are many of their compounds. All of the elements that are ferromagnetic...
by the unpairedelectrons. In a paramagnetic material there are unpairedelectrons; i.e., atomic or molecular orbitals with exactly one electron in them...
state contains one unpairedelectron and shows splitting of spectral lines into a doublet, and a triplet state has two unpairedelectrons and shows threefold...
localized unpairedelectron. To determine the direction to the spin active nucleus from the localized unpairedelectron (remember: unpairedelectrons are,...
unpairedelectron, transitions in a magnetic field can also be observed in which only the spin quantum number changes, without change in the electron...
can be CH• or CH3• (also written as ⫶CH); each dot representing an unpairedelectron. The corresponding systematic names are methylylidene or hydridocarbon(•)...
This gave a better explanation for the transition from localized unpairedelectrons to itinerant ones partaking in metallic bonding. The combination of...
the methyl radical (CH3) which has an unpairedelectron in a non-bonding orbital on the carbon atom and no electron of opposite spin in the same orbital...
with the remaining unpairedelectron on the nitrogen atom, to form a standard covalent bond. The process of transferring the electron from nitrogen to oxygen...
of a molecule or ion resulting from the presence of more than one unpairedelectron. In quantum mechanics, an energy level is called degenerate if it...
radical refers to various free radicals, which are species that have an unpairedelectron and need not be charged.[citation needed] A simple example of a polyatomic...
magnetic moments of the unpairedelectrons of the magnet's material and the nuclear magnetic moments. For an atom, individual electron spins are added to get...
of half filled valence atomic orbitals of each atom containing one unpairedelectron. A valence bond structure is similar to a Lewis structure, but where...
under ambient conditions has two unpairedelectrons. Dioxygen is a triplet molecule, since the two unpairedelectrons allow for three spin states. The...
covalent bond and has three non-bonded electrons. The carbon atom has either one or three unpairedelectrons, depending on its excitation state; making...
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