What is a Delocalised Electron?
“A delocalised electron is an electron in an atom, ion, or molecule that is not connected to a single atom or covalent bond.”
Delocalised electrons in a ring structure are represented by a circle rather than single and double bonds. This means that the electrons could be anywhere along with the chemical bond.
Delocalised electrons contribute to the atom’s, ion’s, or molecule’s conductivity. Materials with a lot of delocalised electrons are usually very conductive.
Table of Contents
- Examples of Delocalized Electrons
- Delocalization Setup
- Resonance
- Electrical Conduction
- Molecular Orbitals
- Difference between Localized and Delocalized Electrons
- Frequently Asked Questions- FAQs
Examples of Delocalized Electron
The double bonds contain pi bonds, which are made of loosely held electrons; this causes the loosely held electrons to move and, as a result, they become delocalized. Delocalization causes higher energy stabilisation in the molecule.
1. In the benzene molecule, as shown below:
The two benzene resonating structures are formed as a result of electron delocalization. As a result, the bond lengths in benzene are all the same, giving this molecule extra stability.
2. A carboxylate group is another example of a delocalized electron, with the negative charge centred equally on the two oxygen atoms.
3. Delocalized electrons can also be found in metal structures.
Delocalization Setup
There are specific structural features that bring up electrons or charge delocalization. The common arrangements are:
(a) The presence of a positive charge next to a pi bond. The positive charge can be on one of the atoms that make up the pi bond, or on an adjacent atom.
(b) The presence of a positive charge next to an atom with lone electron pairs.
(c) The presence of a pi bond next to an atom with lone electron pairs.
Resonance
The delocalization of six electrons over the C6 ring in the simple aromatic ring of benzene is frequently represented by a circle. The fact that the six C-C bonds are equidistant indicates that the electrons are delocalized; if the structure had isolated double bonds alternating with discrete single bonds, the bond would have alternating longer and shorter lengths. Delocalization in benzene is represented by resonance structures in valence bond theory.
Electrical Conduction
- Delocalized electrons are also common in solid metals, where they form a “sea” of electrons that are free to move around. As a result, metals are usually excellent electrical conductors.
- Covalent bonding occurs between the four outer electrons of each carbon atom in the crystal structure of a diamond which is localized. The movement of electrons is restricted and diamond does not conduct an electric current.
- In contrast, only three of the four outer electrons in graphite, another form of pure carbon, are covalently bonded to other carbon atoms. Each carbon atom contains a delocalized electron that participates in chemical bonding but is free to move throughout the molecule’s plane. Because electrons are delocalized in graphite, the molecule conducts electricity along the plane but not perpendicular to it.
Molecular Orbitals
Standard ab initio quantum chemistry methods produce delocalized orbitals that, in general, extend over an entire molecule and have the symmetry of the molecule. Localized orbitals can then be found as linear combinations of delocalized orbitals, as determined by an appropriate unitary transformation.
In methane, for example, the bonding electrons are equally shared by all five atoms. The presence of delocalization is implied by Molecular Orbital Theory.
Difference between Localized and Delocalized Electrons
- A localized atom is an electron that is associated with a specific atom, whereas a delocalized electron is one that is not associated with any single atom or covalent bond.
- Localized electrons are found between atoms and are confined to a specific region between two atoms, whereas delocalized electrons are found above and below the atoms and are spread across several atoms.
- The localized electrons are associated with specific atoms in a compound, whereas the delocalized electrons are associated with all atoms in the molecule.
- Localized electrons are represented graphically by straight lines, whereas delocalized electrons are represented graphically by circles.
Frequently Asked Questions on Delocalized Electron
Define delocalized electrons.
Delocalized electrons are electrons that are not associated with a single atom or covalent bond in a molecule, ion, or solid metal. Delocalized electrons are contained within an orbital that spans several neighbouring atoms.
Benzene is an example.
How do you know if an electron is delocalised?
The simplest way to detect delocalised electrons is to compare electron locations in two resonance forms. Delocalization occurs when a pair appears in one place in one form and another place in another form.
In which bonds are electrons delocalised?
The valence electrons of the interacting metal atoms’ s and p orbitals delocalise in metallic bonds. That is, instead of orbiting their respective metal atoms, the electrons form a “sea” that surrounds the positively charged atomic nuclei of the interacting metal ions. Delocalisation of electrons is not confined to a single bond or a double bond, it is the spread of electrons throughout the conjugated system in a compound, for example in a benzene molecule all the six carbon atoms equally share the electrons present in the molecule.
In a benzene molecule, how many delocalised pi electrons are there?
Three pi bonds have been delocalised. As a result, the number of delocalised electrons is 6.
What causes the delocalisation of electrons?
Conjugation causes electron delocalisation. The more extensive the conjugated system, the more stable is the molecule.
A conjugated system, or conjugated bonds, is the presence of alternating π and 𝜎 bonds in a molecule. Conjugated systems can extend across the entire molecule, or they can only make up a portion of a molecule.
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