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Write about valance bond theory .
Answers
Answer:
Valence bond (VB) theory is a chemical bonding theory that explains the chemical bonding between two atoms. Like molecular orbital (MO) theory, it explains bonding using principles of quantum mechanics. According to valence bond theory, bonding is caused by the overlap of half-filled atomic orbitals. The two atoms share each other's unpaired electron to form a filled orbital to form a hybrid orbital and bond together. Sigma and pi bonds are part of valence bond theory.
Explanation:
Valence bond theory predicts covalent bond formation between atoms when they have half-filled valence atomic orbitals, each containing a single unpaired electron. These atomic orbitals overlap, so electrons have the highest probability of being within the bond region. Both atoms then share the single unpaired electrons to form weakly coupled orbitals.
The two atomic orbitals do not need to be the same as each other. For example, sigma and pi bonds may overlap. Sigma bonds form when the two shared electrons have orbitals that overlap head-to-head. In contrast, pi bonds form when the orbitals overlap but are parallel to each other.
Sigma bonds form between electrons of two s-orbitals because the orbital shape is spherical. Single bonds contain one sigma bond. Double bonds contain a sigma bond and a pi bond. Triple bonds contain a sigma bond and two pi bonds. When chemical bonds form between atoms, the atomic orbitals may be hybrids of sigma and pi bonds.
The theory helps explain bond formation in cases where a Lewis structure can't describe real behavior. In this case, several valence bond structures may be used to describe a single Lewis stricture.
Answer:
Valence bond (VB) theory assumes that all bonds are localized bonds formed between two atoms by the donation of an electron from each atom. This is actually an invalid assumption because many atoms bond using delocalized electrons. In molecular oxygen VB theory predict that there are no unpaired electrons. VB theory does a good job of qualitatively describing the shapes of covalent compounds. While Molecular Orbital (MO) theory is good for understanding bonding in general. It is more difficult to learn, but predicts the actual properties of molecules better than VB theory. MO theory actually predicts electron transitions because of the differences in the energy levels of orbitals in the molecule. MO theory has been more correct in numerous instances and for this reason it is preferred.
Valence Bond theory describes covalent bond formation as well as the electronic structure of molecules. The theory assumes that electrons occupy atomic orbitals of individual atoms within a molecule, and that the electrons of one atom are attached to the nucleus of another atom. This attraction increases as the atoms approach one another until the atoms reach a minimum distance where the electron density begins to cause repulsion between the two atoms. This electron density at the minimum distance between the two atoms is where the lowest potential energy is acquired, and it can be considered to be what holds the two atoms together in a chemical bond.