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

Ever noticed how things around us are attached? Like how water holds oxygen and hydrogen together in one molecule, how oxygen atoms are bonded together in a molecule, forming air to breathe, and how plastics or metals are so strong. So, the only reason behind all these is chemical bonding. A force that is there to hold atoms together in a molecule. There are various types of bonding among atoms, but sigma and pi bonds are fundamental bonds that are the main force behind the structure and stability of the molecule. When there is direct or head-on overlapping of atomic orbitals, then a sigma bond is formed, which represents the strongest type of covalent bond and forms the basis of molecular structures. While sideways overlapping of atomic orbitals leads to the formation of pi-bonds. Pi-bonds are always accompanied by sigma bonds in double and triple bonds.

This Story also Contains

1. What is a sigma bond? or sigma meaning
2. Example of Sigma Bond:
3. Examples of Pi bonds:
4. Types of Overlapping:
5. Organometallic Compounds:
6. Sigma-bonded organometallic compounds:
7. Pi-bonded organometallic compounds:
8. Sigma bond vs Pi bond:

For example, a doubly bonded oxygen molecule has one sigma bond and one pi bond, while a triple-bonded N₂ molecule has 1 sigma bond and two pi bonds. Everything around us, like oxygen in air, atoms of carbon in polythene, carbon in coal or diamond, is bonded in one way or another. The strengths and weaknesses of elements are based on the type of bonding between the atoms of that element.

Formation of Sigma and Pi Bond:

The hybridization helps in predicting such complex models of squeezing electrons into the same space of a sphere by concluding all the Sigma Bonds. The structure of ethane consists of C-C single bonds and C-H single bonds, while the structure of ethene has a double bond between C-C and a single bond between C-H, and so the geometry of such a covalent compound is planar. In the above figure, the hybridization found is sp² where whereas in the case of ethane 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 a covalent bond. The bonding in ethene can be summarized as follows: The three sp² hybrids overlap with other orbitals of the carbon atom that are identical. The remaining two hybrid orbitals form the bond with the hydrogen atom by overlapping with 1s orbital. Hence, the 2pz on the carbon atom forms the other bond at a sideways of one another.

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What is a sigma bond? or sigma meaning

So, in the 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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