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C2H4, also known as ethylene or ethene, is created in the world by the method of steam cracking. It is also released in trace amounts by plants to signal their fruits to ripen. Ethene has the carbon hybrized to the sp2 configuration. Ethene is a great example of an alkene because the sp2 orbitals on the carbon are bonded to a carbon and two hydrogens each. The remaining p orbital is used for a pi bond which is responsible for the reactivity of this alkene.  

  1. 1. Introduction
  2. 2. Lewis Structures
  3. 3. VSEPR Theory
  4. 4. References
  5. 5. Outside Links
  6. 6. Problems
  7. 7. Contributors

Introduction


In 1916 G. N. Lewis proposed that a chemical bond is formed by the valence electrons of atoms which would prove fundamental in the valence bond theory. We all remember our first alkene discussed in Organic Chemistry and it was usually C2H4. This is becuase ethene is the smallest alkene and how it is also planar. The Valence Bond theory will show us how the bonds in C2H4 come together. Two things that will help us utilize the Valence Bond Theory effectively are familiarity with Lewis Structures and VSEPR theory.

Lewis Structures


A key component of using Valence Bond Theory correctly is being able to use the Lewis Dot diagram correctly. This also requires the knowledge of hybridization of each molecule, which will help you find what angles the bonds are at and what orbitals are used. For Ethene, you have two carbon atoms double bonded to each other and two hydrogen atoms bonded to each carbon atom. This looks something like this: 

As you can see ethene has two bonds between the carbons and one bond between the hydrogen and carbon. Also each carbon has an octet and the hydrogens have a pair of electrons. For more information on how to use Lewis Dot Structures refer to http://chemwiki.ucdavis.edu/Wikitexts/UCD_Chem_124A%3a_Kauzlarich/ChemWiki_Module_Topics/Lewis_Structures.

VSEPR Theory


Using the Valence Shell Electron Pair Repulson (VSEPR) Theory we can predict the bond angles and positions of the carbons and hydrogens of ethene. We can  also tell how many bonds are formed between the carbons - the bond order. Using the theory we get AX3 which corresponds to teh trigonal planar geometry and shape of the molecule. Now we can deduce that the C2H4 is a planar molecule and that the degrees between each bond are ~ 120., as you can see in the picture below.

According to the Valence Bond theory a covalent bond is formed between the two atoms by the overlap of half filled valence atomic orbitals of each atom containing one unpaired electron. All four hydrogens have one unpaired electrons and the carbons are hybrized sp3 so they each have one electron in each of the  three sp3 orbitals. The fourth electron is in the p orbital that will form the pi bond. The bond order for ethene will simply be how many bonds are between each atom. A bond order of two for the carbon carbon bond and a bond order of one between the carbon hydrogen bond. For more information see  http://chemwiki.ucdavis.edu/Wikitexts/UCD_Chem_124A%3a_Kauzlarich/ChemWiki_Module_Topics/VSEPR



The diagram below shows the different bond lengths and the bond angle due to the bonding of the carbons and the hydrogens.



References


     
  1. Murrel, J. N.; S. F. Tedder (1985). The Chemical Bond. John Wiley & Sons.      
    2.  
  2. Shaik, Sason S.; Phillipe C. Hiberty (2008). A Chemist's Guide to Valence Bond Theory. New Jersey: Wiley-Interscience


 
 

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