With respect to bonding theories, the Lewis model, valence bond theory, and molecular orbital all define a single chemical bond in different ways. In the Lewis model a single bond consists of two electrons which are shared by two atoms. In valence bond theory a single bond is two orbital’s which are weakly coupled, meaning they have a small overlap, this is also known as a sigma bond. Finally molecular orbit theory electrons occupy specific orbital, either bonding or anti-bonding. A single bond is defined as a bond order of 1, meaning that it is made up of electrons in the bonding orbital’s minus electrons in the anti-binding orbital’s (Tro, 2017).
For double bonds the Lewis model defines a double bond as consisting of four electrons being shared by two atoms. In valence bond theory a double bond consists of two bonds: a sigma bond and a pi bond. Finally molecular orbital theory defines a double bond as a bond order of 2 (Hurst, 2002).
For triple bonds the Lewis model defines a triple bond as consisting of six electrons being shared by two atoms. In valence bond theory a triple bond consists of three bonds: a single sigma bond and an additional two pi bonds. Finally molecular orbital theory defines a triple bond as a bond order of 3 (Gillespie, 2004).
All of these definitions are similar in that all theories use electrons to define the type of bond. As well while the theories describe differences in how the electrons form bonds all theories require two electrons for a single bond (Tro, 2017).
All of these definitions are different because they describe bonding in different ways. In Lewis, the electrons are directly shared, whereas in the other two theories it is orbital’s in which the electrons are in which are shared between the atoms to form the bonds (Tro, 2017).
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"Molecular Structure".
- Gillespie, R. J. (2004). Teaching molecular geometry with the VSEPR model. J. Chem. Educ, 81(3), 298.
- Hurst, M. O. (2002). How we teach molecular structure to freshmen. J. Chem. Educ, 79(6), 763.
- Tro, N. J. (2017). Chemistry: A Molecular Approach (4 ed.): Pearson
