Presentation on theme: "Hybrid Orbitals: Bonding in Complex Molecules 1-8 Mixing of atomic orbitals from the same atom results in new atomic orbitals of different energy and directionality."— Presentation transcript:
Hybrid Orbitals: Bonding in Complex Molecules 1-8 Mixing of atomic orbitals from the same atom results in new atomic orbitals of different energy and directionality. sp Hybrids produce linear structures. An incorrect structure for BeH 2 is predicted if 2s and 2p orbitals of Be are overlapped with the 1s orbitals of H:
Mixing the 2s orbital with one of the 2p orbitals of Be results in two new hybrid sp orbitals, each made up of 50% s and 50% p character. The resulting bond angle is 180 o which corresponds with the observed bond angle in the BeH 2 molecule. Hybridization does not change the number of orbitals on the atom. In this case two atomic orbitals are replaced by two new hybrid orbitals. The two un- hybridized p orbitals are still available to hold electrons.
sp 2 Hybrids create trigonal structures. Hybridization of a 2s and two 2p orbitals results in three new hybrid orbitals that point to the corners of an equilateral triangle. The remaining p orbital points up and down, perpendicular to each of the three hybrid orbitals. Bond angles in molecules using sp 2 hybridization are approximately 120 o The molecule, BH 3 is isoelectric with the methyl cation, CH 3 +. Both involve sp 2 hybridization about the central atom.
sp 3 Hybridizaton explains the shape of tetrahedral carbon compounds. When the 2s and all three 2p orbitals are hybridized, four hybrid orbitals called sp 3 orbitals are formed. These orbitals point to the corners of a regular tetrahedron. Bond angles in molecules using sp 3 hybridization are approximately 109.5 o
Hybrid orbitals may contain lone electron pairs: ammonia and water. Not all hybrid orbitals participate in bond formation. Some may contain lone pairs of electrons. The bond angles in ammonia are 107.3 o and that in water is 104.5 o, both close to 109.5 o. The slightly smaller bond angles in ammonia and water are due to the slightly larger volume requirements for lone pair electrons, which forces the remaining bonding pair electrons closer together.
Pi bonds are present in ethene (ethylene) and ethyne (acetylene). Molecules containing double or triple bonds contain unhybridized p orbitals that overlap lengthwise rather than end on.