Valence Bond Theory Hybridization Polarity Intermolecular Forces Mr
Valence Bond Theory, Hybridization Polarity Intermolecular Forces Mr. Krstovic SCH 4 UO
Valence Bond Theory • A covalent bond is formed by the overlapping of two half filled valence atomic orbitals of two different atoms • The electrons in the overlapping orbitals get paired and confined between the nuclei of two atoms. • There are two types of covalent bonds based on the pattern of overlapping: SIGMA (σ)-BOND or Pi (π)BOND
Sigma Bonds The covalent bond formed due to overlapping of atomic orbital along the inter nucleus axis is called σ-bond.
Pi-Bonds • The covalent bond formed by sidewise overlapping of atomic orbitals is called πbond.
N 2 molecule • The ground state electronic configuration of N is [He] 2 s 2 2 px 1 2 py 1 2 pz 1.
• Theoretical process involving the mixing of atomic orbitals to create a new set of orbitals that take part in covalent bonding • Mainly useful for describing the shapes of organic compounds
…helps to explain the molecular shape of CH 4 • CH 4 is tetrahedral • Bond angle is 109. 5 o • WHY? • Answer: Hybridization of carbon's s and p orbitals
Electron Configuration in Carbon
CH 4 – hybridization of Carbon 2 s orbital + 3 2 p orbitals → 4 hybridised sp 3 orbitals
sp 3 hybridization
Case of H 2 O Molecule • H 2 O is also tetrahedral (counting the lone pair of electrons) • sp 3 hybridization • Angle less then 109. 5 because lone the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together. The result is a distorted tetrahedral arrangement in which the H —O—H angle is 104. 5°
sp hybridization for linear molecules • Explains why Be. Cl 2 is linear (1800 bond angle)
sp 2 hybridization for trigonal planar
Polarity of Molecules
Using dipole moment vectors Since there is a resultant dipole vector, the molecule is POLAR
Non-polar molecules
Polar Molecules
Test your skill… • Polar or non-polar? Draw the structure, determine shape and use dipole vectors to determine polarity: • CHCl 3 (chloromethane) • SO 3
Answers:
H-bonding
Practice Questions 1. Predict which compound in each pair will have the higher melting point. (a) HI or KI (b) HCl or H 2 O (c) CH 4 or NH 3 (d) CHCl 3 or CF 4
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