Valence Bond theory & Hybridization

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  • 1. Valence Bond Theory & Hybridization T- 1-855-694-8886 Email- info@iTutor.com By iTutor.com
  • 2. The valence bond theory was proposed by Heitler and London to explain the formation of covalent bond quantitatively using quantum mechanics. Later on, Linus Pauling improved this theory by introducing the concept of hybridization. Valence bond (VB) theory assumes that all bonds are localized bonds formed between two atoms by the donation of an electron from each atom.
  • 3. Valence Bond theory describes covalent bond formation as well as the electronic structure of molecules. The theory assumes that electrons occupy atomic orbital's of individual atoms within a molecule, and that the electrons of one atom are attracted to the nucleus of another atom.
  • 4. A covalent bond is formed by the overlapping of two half filled valence atomic orbital's of two different atoms. The electrons in the overlapping orbital's get paired and confined between the nuclei of two atoms. The electron density between two bonded atoms increases due to overlapping. This confers stability to the molecule.
  • 5. Greater the extent of overlapping, stronger is the bond formed. The direction of the covalent bond is along the region of overlapping of the atomic orbital's i.e., covalent bond is directional.
  • 6. σ-bond A sigma bond (symbol: σ) is a covalent bond formed via linear overlap of two orbital's. π-bond A pi bond (symbol: π) is a covalent bond formed via parallel overlap of two orbital's. There are two types of covalent bonds based on the pattern of overlapping as follows: Π bond
  • 7. The covalent bond formed due to overlapping of atomic orbital along the inter nucleus axis is called σ-bond. It is a stronger bond and cylindrically symmetrical. Depending on the types of orbital's overlapping, the σ- bond is divided into following types: (i): σs-s bond, (ii): σp-p bond, (iii): σs-p bond:
  • 8. σs-s bond:
  • 9. σp-p bond:
  • 10. σs-p bond:
  • 11. The covalent bond formed by sidewise overlapping of atomic orbital's is called π- bond. In this bond, the electron density is present above and below the inter nuclear axis. It is relatively a weaker bond since the electrons are not strongly attracted by the nuclei of bonding atoms. Note: The 's' orbital's can only form σ-bonds, whereas the p, d & f orbital's can form both σ and π-bonds.
  • 12. The electronic configuration of hydrogen atom in the ground state is 1s1. In the formation of hydrogen molecule, two half filled 1s orbital's of hydrogen atoms overlap along the inter- nuclear axis and thus by forming a σs-s bond.
  • 13. The electronic configuration of Cl atom in the ground state is [Ne]3s2 3px 2 3py 2 3pz 1. The two half filled 3pz atomic orbital's of two chlorine atoms overlap along the inter-nuclear axis and thus by forming a σp-p bond.
  • 14. In the ground state, the electronic configuration of hydrogen atom is 1s1. And the ground state electronic configuration of Cl atom is [Ne]3s2 3px 2 3py 2 3pz 1. The half filled 1s orbital of hydrogen overlap with the half filled 3pz atomic orbital of chlorine atom along the inter- nuclear axis to form a σs-p bond.
  • 15. The electronic configuration of O in the ground state is [He] 2s2 2px 2 2py 1 2pz 1. The half filled 2py orbital's of two oxygen atoms overlap along the inter-nuclear axis and form σp-p bond. The remaining half filled 2pz orbital's overlap laterally to form a πp-p bond.
  • 16. Thus a double bond (one σp-p and one πp-p) is formed between two oxygen atoms.
  • 17. The ground state electronic configuration of N is [He] 2s2 2px 1 2py 1 2pz 1. A σp-p bond is formed between two nitrogen atoms due to overlapping of half filled 2px atomic orbital's along the inter-nuclear axis.
  • 18. The remaining half filled 2py and 2pz orbital's form two πp-p bonds due to lateral overlapping. Thus a triple bond (one and two) is formed between two nitrogen atoms.
  • 19. The intermixing of two or more pure atomic orbital's of an atom with almost same energy to give same number of identical and degenerate new type of orbital's is known as hybridization. The new orbital's formed are also known as hybrid orbital's. During hybridization, the atomic orbital's with different characteristics are mixed with each other.
  • 20. sp sp2 sp3 sp3d sp3d2 sp3d3
  • 21. Intermixing of one 's' and one 'p' orbital's of almost equal energy to give two identical and degenerate hybrid orbital's is called 'sp' hybridization. These sp-hybrid orbital's are arranged linearly at by making 180 ⁰ of angle. They possess 50% 's' and 50% 'p' character.
  • 22. Intermixing of one 's' and two 'p' orbital's of almost equal energy to give three identical and degenerate hybrid orbital's is known as sp2 hybridization. The three sp2 hybrid orbital's are oriented in trigonal planar symmetry at angles of 120 ⁰ to each other. The sp2 hybrid orbital's have 33.3% 's' character and 66.6% 'p' character.
  • 23. In sp3 hybridization, one 's' and three 'p' orbital's of almost equal energy intermix to give four identical and degenerate hybrid orbital's. These four sp3 hybrid orbital's are oriented in tetrahedral symmetry with 109 ⁰ 28' angle with each other. The sp3 hybrid orbital's have 25% ‘s’ character and 75% 'p' character.
  • 24. In sp3d hybridization, one 's', three 'p' and one 'd' orbital's of almost equal energy intermix to give five identical and degenerate hybrid orbital's, which are arranged in trigonal bipyramidal symmetry. Among them, three are arranged in trigonal plane and the remaining two orbital's are present above and below the trigonal plane at right angles. The sp3d hybrid orbital's have 20% 's', 60% 'p' and 20% 'd' characters.
  • 25. Intermixing of one 's', three 'p' and two 'd' orbital's of almost same energy by giving six identical and degenerate hybrid orbital's is called sp3d2 hybridization. These six sp3d2 orbital's are arranged in octahedral symmetry by making 90 ⁰ angles to each other. This arrangement can be visualized as four orbital's arranged in a square plane and the remaining two are oriented above and below this plane perpendicularly.
  • 26. In sp3d3 hybridization, one 's', three 'p' and three 'd' orbital's of almost same energy intermix to give seven sp3d3 hybrid orbital's, which are oriented in pentagonal bipyramidal symmetry. Five among the sp3d3 orbital's are arranged in a pentagonal plane by making 72⁰ of angles. The remaining are arranged perpendicularly above and below this pentagonal plane.
  • 27. ē Pair Hybridization Shape 2 sp linear 3 sp2 trigonal planar 4 sp3 tetrahedral, pyramidal, or bent 5 sp3d trigonal bipyramidal, trigonal planar, or linear 6 sp3d2 octahedral, square planar, or linear
  • 28. Call us for more Information: www.iTutor.com Visit 1-855-694-8886