Sigma and Pi Bond - Formation, Examples, Overlapping with FAQs

Sigma Bond and Pi Bond:

Imagining two electrons in a space of sphere is possible when they are interacting with each other. In this case while considering double and triple bonds in same space of sphere visualizing that condition of squeezing more electrons in same space is difficult to work. Electrons did not work when they are squeezed or pushed together as they bear the same charges i.e negative charge. So for this situation we require different complex visualization for all these electrons to work.

Formation of Sigma and Pi Bond:

The hybridization helps in predicting such complex models of squeezing electrons in same space of sphere by concluding all the Sigma Bonds. The double and triple bonds rea included in the structure of Ethene. Ethene is covalent bond having double bond in between C-C and single bond in between C-H, and so geometry of such covalent compound is planar. In the above figure the hybridization found is sp2 where as in case of methane hybridization was sp3.

Thus we can see that in ethene generation of 2pz unhybridized orbital with each orbital contains one electron which is capable of forming covalent bond. The bonding in ethene can be summarize as follows: The three sp2 hybrids overlaps with other orbital of carbon atom that are identical. Remaining two hybrid orbitals forms the bond with hydrogen atom by overlapping with 1s orbital. Hence the 2pz on carbon atom forms the other bond with sideways of one another.

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What is a sigma bond? or sigma meaning

So, in above discussion it is mandatory to distinguish the two covalent bond formed in ethene. The single bond formed is termed as Sigma Bond. Sigma bond can be represented as "σ". The bond formed by the cation of end to end overlap of sigma bonds, where the concentrated density of electrons was found in nuclei of atom and the bonding atoms. Six sigma bonds are formed in total out of which three are bonded with carbon atoms in the molecule. Sigma bonds are formed as end to end which means the overlapping is done coaxially. Such type of overlapping is called axial overlapping.

Example of Sigma Bond:

Sigma bond can be seen in the formation of hydrogen molecule. This can be seen in the picture depicted below where hydrogen bonded singly as sigma bond.

Pi Bond:

The pi bond is the second bond that is formed in between C-C atom and are elongated on both above and below the plane of the molecule. As according to Lewis dot structure, double bond which is formed in between molecule can be represented by single dash. Pi bond can be represented as π.In pi bond the electron density is concentrated on both above and below of the plane of nuclei of bonding atoms. Therefore, it is noted that the two bonds are formed sigma bond and pi bond in covalent molecule of ethene. In general, when single bond is present in between the two atoms it is sigma bond where as double bonds are comprising of one sigma bond and one pi bond. In case of triple bonds one sigma and two pi bonds are present.

Examples of Pi bonds:

Ethyne bonding is the ones such example of pi bonding, which is singly bonded with one hydrogen atom and triple bonds are present mong carbon atoms. The bonds are formed by electron transfer of specific wavelength of 2s electron to 2pz.Here one 2s orbital will combine with one 2p orbital to form sigma bond and sp hybridization whereas the remaining 2py and 2pz forms the pi bond.

What are Sigma and Pi bonds?

The names are derived from the Greek letters. The sigma and pi bonds both are used to predict the molecules behaviour as according to molecular orbital theory. In sigma bond, the orbitals are as similar as according to “s” where as in pi bond the orbital is similar with p orbitals. It is found that sigma bonds are stronger in comparison with pi bonds.

Types of Overlapping:

Direct overlapping can be seen in sigma bonds. The electrons which are participating in bond formation are termed as sigma electrons. Singly bonded electrons are formed as according to the combination of atomic orbitals as follows:

S-S overlapping-:

In such type of overlapping one ‘s; orbital will participate along internuclear axis which means head-on overlapping. This can be represented as follows:

S-P overlapping-:

In such type of overlapping occur along internuclear axis when one half-filled p orbital overlaps with one half fille s orbital, and forms the covalent bond. Such condition can be represented as follows:

P-P overlapping-:

In such type of overlapping occur along internuclear axis when one half filled orbital will undergoes head-on overlapping. Such condition can be represented as follows:

Organometallic Compounds:

Sigma bonded organometallic compounds are defined as those compounds that are formed by the help of metal ‘M’ and carbon of the ligands containing covalent sigma bond, are termed as Sigma bonded organometallic compounds. Here the metal can be bonded to any alkyl family, aryl family or pi-bonded ligands. These organometallic compounds are basically divided as according to metal-carbon bond as follws:

• Sigma bonded organometallic compounds

• Pi bonded organometallic compounds

Sigma bonded organometallic compounds:

The sigma bonded organometallic compounds are those compounds that contains metal-carbon with covalent sigma bond so they are termed as sigma bonded organometallic compounds. Example of such sigma bonded organometallic compounds are Grignard reagents, which has general structure as R-Mg-X here R is an organic group and X is halogen compound. In this example covalent sigma bond is present in metal that is magnesium and R any aryl or alkyl.

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Pi bonded organometallic compounds:

Taking an example of ferrocene compound in which the two Fe- (C2H5) bonds. The compound Fe is bonded in pi bond system thus ferrocene is bonded in pi bonded organometallic compound.

Sigma bond vs Pi bond:

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NCERT Chemistry Notes:

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