If the ethylene molecules are reviewed according to the concept of molecular orbitals, carbon in the molecule using sp2 orbital to form bonds with three other atoms. Orbital hybridisation sp2 emerged from 2s1, 2px1, and 2py1. Each of the three carbon atoms of ethylene binding through σ bonds, one to each hydrogen atom, and one to the other carbon. Each carbon atom has one electron in the 2pz orbital, and based on the principle of maximum repulsion then the orbital is perpendicular to the plane of sp2 orbitals. Two parallel 2pz orbitals overlap laterally to produce two new hybrid orbitals, the π bonding orbital and orbital anti-bonding π *. Orbital σ ellipsoid-shaped and symmetrical around the axis CC.orbitals Π in the form of two ellipsoid, one above and one below. Own field declared node. To maintain maximum fixed p orbitals overlap, the orbitals must be parallel. This means that the free rotation around the double bond is not possible. The six atoms on the double bond system is located in one corner of the field with less than 120o. Double bond is shorter than the single bond of the same atoms for maximum stability is achieved when orbitals p overlap maximum extent possible. Double bond carbon-carbon-oxygen and nitrogen are also similar, comprising one σ bond and one π bond.
fig. orbitals P overlap to produce bonding and π π *
In the triple bond compounds, carbon atoms only bind two others and therefore hybridize sp carbon. This means that all four atoms lie in a straight line. Each carbon atom has two p orbitals are filled with one electron. Orbitals are perpendicular to each other and to the axis CC. A triple bond consists of one σ orbitals and two π orbitals. Something similar is found in the three-carbon double bond with nitrogen.
Fig. orbitals P overlap in a triple bond.
Double bond and three only important for the elements of the second period which carbon, nitrogen, and oxygen. For the elements of the third period, rarely double bonds formed and the compounds containing double bonds are generally not stable because the p orbitals which will membentukan double bond away from each other so that overlapnya less. Only the double bond C = S is an important element of the third period, and compounds containing C = S bond is much less stable than the compound C = O.
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