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hokhani
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Bonds in molecules
What is the meaning of the bonds σ and π in molecules quantum mechanically?
What is the meaning of the bonds σ and π in molecules quantum mechanically?
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hokhani said:What is the meaning of the bonds σ and π in molecules quantum mechanically?
Thank you very much. I like to know how to calculate angular momentum in molecular orbitals. Could you please give me a reference for that?DrClaude said:Consider a molecular orbital in a diatomic molecule. The projection of the angular momentum of an electron in that orbital on the internuclear axis is designated by the quantum number ##\lambda##. In analogy with hydrogenic orbitals, the value of this quantum number is expressed with a letter according to
$$
| \lambda | = 0 \Rightarrow \sigma \\
| \lambda | = 1 \Rightarrow \pi \\
| \lambda | = 2 \Rightarrow \delta \\
\vdots
$$
(note the absolute value, as the projection can be positive or negative).
For polyatomic molecules, a similar concept is applied in LCAO-MO theory where the molecular orbitals are built two atoms at a time.
An easy way to identify the value of ##| \lambda |## is to look along the bond and count the number of nodal planes. A ##\sigma## bond will look circular, a ##\pi## bond will be in the shape of a 8, similar to a p orbital in an atom.
Thank you. I will get it.DrDu said:Landau Lifgarbagez, Quantum Mechanics, has a good discussion of the states of diatomic molecules apt for physicists.
Sigma (σ) bonds are formed by the head-on overlap of atomic orbitals, while pi (π) bonds are formed by the side-by-side overlap of atomic orbitals. This difference in overlap leads to different bonding characteristics and strengths.
Quantum mechanics describes the behavior of electrons in atoms and molecules. In this theory, the formation of σ and π bonds is explained by the overlap of atomic orbitals and the concept of electron density, which determines the strength of the bond.
Yes, most molecules have both σ and π bonds. This is because the formation of multiple bonds between atoms often involves both types of overlap. For example, a double bond consists of one σ bond and one π bond, while a triple bond consists of one σ bond and two π bonds.
The presence and strength of σ and π bonds can greatly influence the physical properties of a molecule. For example, molecules with strong π bonds tend to have higher melting and boiling points due to their increased stability. Additionally, the presence of π bonds can also affect the reactivity and chemical behavior of a molecule.
Yes, the strength of σ and π bonds can be calculated using quantum mechanical equations and principles. This allows scientists to predict and understand the bonding properties of different molecules and their behavior under various conditions.