This compound is known but is extremely reactive. way to explain this is to postulate that an excited electronic state of carbon forms – PowerPoint PPT. Theories of Covalent Bonding. If you are doing this lecture “online” then print the lecture notes available as a word document, go through this ppt lecture, and do. Theories of Covalent Bonding Valence Shell Electron Pair Repulsion Theory Valence Bond (VB) Theory and Orbital Hybridization
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Lewis proposed that a chemical bond forms by the interaction of two shared bonding electrons, with the representation of molecules as Lewis structures.
Valence bond theory - Wikipedia
In the Heitler — London theory was formulated valence bond theory ppt to for the first time enabled the calculation of bonding properties of the hydrogen molecule H2 based on quantum mechanical considerations.
He then called up his associate Fritz London and they worked out the details of the theory over the course of the night. According to Charles Coulsonauthor of the noted book Valence, this period marks the start of "modern valence bond theory", as contrasted with older valence bond theories, which are essentially electronic theories of valence couched in pre-wave-mechanical terms.
Resonance theory was criticized valence bond theory ppt to imperfect by Soviet chemists during the s. A valence bond structure is similar to a Lewis structurebut where a single Lewis structure cannot be written, several valence bond structures are used.
Each of these VB structures represents a specific Lewis structure.
This combination of valence bond structures is the main point of resonance theory. Valence bond theory considers that the overlapping atomic orbitals of the participating atoms form a chemical bond. Because of the overlapping, it is most probable that electrons should be in the bond region.
Valence bond theory views bonds as weakly coupled orbitals small overlap. Valence bond theory is typically easier to employ in ground state molecules.
Valence bond theory
The inner-shell orbitals and electrons remain essentially unchanged during the formation of bonds. The overlapping atomic orbitals can differ. The two types of overlapping orbitals are sigma and pi.
Sigma bonds occur when the orbitals of two shared electrons overlap head-to-head. Pi bonds occur when two orbitals overlap when they are parallel.
Valence Bond Theory and Molecular Orbital Theory
For example, a bond between two s-orbital electrons is a sigma bond, because two spheres are always coaxial. The bond strength depends on the attraction of nuclei for the shared electrons, so the greater the orbital overlap, the stronger the bond.
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HF direct overlap of the s and p orbitals of isolated ground state atoms. CH4 4 hydrogen atoms are bonded to a central carbon atom - hybridization happens to obtain the correct bond angles.
Valence Bond Theory and Molecular Orbital Theory - ppt video online download
Pauling proposed that the valence atomic orbitals in the molecule are different from those in the isolated atoms.
We call this Hybridization!
Hybridization occurs to minimize electron pair repulsions when atoms are brought together to form molecules. This results in a double bond. Overlapping of two 1s atomic orbital Example: Overlapping of two px atomic orbital bonding antibonding 33 3.