sigma and pi bond - Overview, Structure, Properties & Uses

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

Edited By Team Careers360 | Updated on Jul 02, 2025 04:53 PM IST

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.

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What is a sigma bond? or sigma meaning
Example of Sigma Bond:
Examples of Pi bonds:
Types of Overlapping:
Organometallic Compounds:
Sigma-bonded organometallic compounds:
Pi-bonded organometallic compounds:
Sigma bond vs Pi bond:

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

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-S overlapping

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:

S-P overlapping

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:

P-P overlapping

Related topics,

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:

Parameters	Sigma Bond	Pi Bond
Bond Formation	The sigma bonds are formed as axially overlapping of atomic orbitals.	The pi bonds are formed as lateral overlapping of atomic orbitals.
Overlapping orbitals	Sigma bonds overlapping of bonds: one hybrid orbital with two hybrid orbitals or one pure orbital with two hybrid orbitals.	Pi bonds overlap of bonds: alternating orbitals.
Existence	Independent	Always with sigma bonds
Bond strength	Stronger than pi bonds	Less stronger than sigma bonds
Number of bonds	Single sigma bond between two atoms	Two pi bonds between two atoms
Number of bonds in a double bond	One sigma bond is present in a double bond.	Only one pi bond is present in a double bond
Number of bonds in a triply bonded atom	One sigma bond in a triply bonded atom	Two pi bonds are there in triply bonded atoms.
Shape of the molecule	Shape can be determined by the sigma bond	No determination of shape is possible through pi bonds.
Order of formation of bonds	First sigma bonds are formed when atoms come closer	First, the sigma bonds are formed then pi bonds

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. What is a sigma bond?

It is a type of covalent bond, and it forms when there is direct or head-on overlapping of atomic orbitals. Sigma bonds are strong bonds, and they are the first bonds formed between atoms.

2. What is a sigma bond?

A sigma bond is a type of covalent bond formed by the head-on overlapping of atomic orbitals. It is characterized by its cylindrical symmetry around the internuclear axis and is the strongest type of covalent bond.

3. What is a pi-bond?

Pi-bonds are formed by the sideways overlapping of atomic orbitals. Pi-bonds are always accompanied by sigma bonds in double and triple bonds.

4. What is the difference between sigma and pi bonds?

Sigma bonds are strong bonds, and they are the first bonds formed between atoms. They form when there is direct or head-on overlapping of atomic orbitals.

Pi bonds are weak bonds. Pi-bonds are formed by the sideways overlapping of atomic orbitals.

5. Can a molecule have only a Pi-bond?

No, a molecule cannot have only a pi bond; they are always accompanied by sigma bonds. For example, in a doubly bonded molecule, one bond is a sigma bond and the other bond is a pi bond, while in a triply bonded molecule, one bond is a sigma bond, while the other 2 bonds are pi bonds.

6. How shape of a molecule depends upon sigma and pi bonds.

Sigma and pi bonds together influence the geometry of molecules. Sigma bonds can rotate freely around the bond axis, allowing for a range of conformations. However, pi bonds restrict this rotation due to their electron clouds being located above and below the bond axis, creating a planar structure. This essential difference in behavior helps define the overall shape of the molecule, impacting its chemical properties and reactivity.

7. What is hyperconjugation and how does it relate to sigma and pi bonds?

Hyperconjugation is the interaction between a sigma bond (usually C-H) and an adjacent empty or partially filled p orbital or pi bond. It provides additional stability to molecules through partial delocalization of sigma electrons.

8. How do sigma and pi bonds influence a molecule's melting and boiling points?

Molecules with more pi bonds often have higher melting and boiling points due to stronger intermolecular forces, particularly in conjugated systems. However, molecular shape and polarity, influenced by sigma bonds, also play crucial roles.

9. Can sigma bonds rotate freely? What about pi bonds?

Sigma bonds generally allow free rotation around the bond axis. Pi bonds, however, restrict rotation because it would disrupt the sideways overlap of p orbitals. This is why double bonds exhibit geometric isomerism.

10. What is the significance of sigma and pi bonds in conjugated systems?

In conjugated systems, alternating single and double bonds allow for delocalization of pi electrons across the entire system. This leads to increased stability, unique spectroscopic properties, and special reactivity patterns.

11. How do sigma and pi bonds affect a molecule's infrared (IR) spectrum?

Both sigma and pi bonds contribute to a molecule's IR spectrum. However, pi bonds often lead to more intense absorption bands due to their greater polarizability. The stretching frequencies of double and triple bonds are characteristic in IR spectroscopy.

12. Can you have multiple pi bonds in a molecule?

Yes, molecules can have multiple pi bonds. For example, a triple bond consists of one sigma bond and two pi bonds. Conjugated systems can also have multiple pi bonds spread across the molecule.

13. Can you describe the process of pi bond formation in ethene (C2H4)?

In ethene, each carbon is sp2 hybridized, leaving one unhybridized p orbital per carbon. These p orbitals overlap sideways to form a pi bond, while the sp2 orbitals form sigma bonds with hydrogen and between carbons.

14. What is the difference between localized and delocalized pi bonds?

Localized pi bonds are confined between two specific atoms, like in ethene. Delocalized pi bonds spread electron density over multiple atoms, as seen in benzene or other aromatic compounds, leading to increased stability.

15. How does the presence of pi bonds affect a molecule's dipole moment?

Pi bonds can contribute significantly to a molecule's dipole moment due to their electron-rich nature. In symmetrical molecules like ethene, the pi bond doesn't create a dipole, but in polar molecules, pi bonds can enhance the overall dipole moment.

16. How do sigma and pi bonds contribute to a molecule's UV-Vis spectrum?

Pi bonds, especially in conjugated systems, are responsible for most UV-Vis absorption. The energy gap between π and π* orbitals corresponds to wavelengths in the UV-Vis region. Sigma bonds typically absorb at much shorter wavelengths.

17. How do sigma and pi bonds affect a molecule's ability to conduct electricity?

Pi bonds, especially in conjugated systems, can significantly enhance a molecule's ability to conduct electricity. Delocalized pi electrons can move more freely through the molecule, while sigma bonds generally do not contribute to conductivity.

18. What is the difference between σ-π and π-π interactions?

σ-π interactions involve the overlap of a sigma orbital with a pi orbital, often seen in hyperconjugation. π-π interactions occur between pi systems of different molecules or parts of a molecule, contributing to intermolecular forces and molecular stacking.

19. How do sigma and pi bonds affect a molecule's heat of formation?

Both sigma and pi bonds contribute to a molecule's heat of formation. Sigma bonds generally contribute more to overall stability due to their strength. However, pi bonds can significantly affect stability through delocalization effects, particularly in conjugated or aromatic systems.

20. What is the role of sigma and pi bonds in pericyclic reactions?

In pericyclic reactions, both sigma and pi bonds are involved in concerted electron reorganization. Pi bonds often serve as the reactive centers, while sigma bonds may be broken or formed during the reaction. The conservation of orbital symmetry, crucial in these reactions, involves both sigma and pi orbitals.

21. How do sigma and pi bonds affect a molecule's magnetic properties?

Pi bonds, especially in conjugated systems, can contribute to a molecule's diamagnetic or paramagnetic properties. Delocalized pi electrons can create ring currents in aromatic compounds, influencing their response to magnetic fields. Sigma bonds generally have less influence on magnetic properties.

22. Can you describe the bonding in acetylene (C2H2) in terms of sigma and pi bonds?

Acetylene has a triple bond between carbon atoms, consisting of one sigma bond and two pi bonds. Each carbon is sp hybridized, forming sigma bonds with hydrogen and between carbons. The remaining two p orbitals on each carbon form two perpendicular pi bonds.

23. How do sigma and pi bonds influence a molecule's stability?

Sigma bonds provide the basic structural stability of a molecule. Pi bonds can enhance stability through electron delocalization, especially in conjugated or aromatic systems. However, pi bonds are also often sites of reactivity due to their higher energy electrons.

24. How do sigma and pi bonds contribute to molecular geometry?

Sigma bonds determine the basic skeletal structure of a molecule, while pi bonds can influence the planarity and rigidity of certain parts of the molecule, often restricting rotation around the bond.

25. How do sigma and pi bonds contribute to aromaticity?

Aromaticity requires a planar, cyclic system with 4n+2 pi electrons (Hückel's rule). The sigma bonds form the ring structure, while the continuous, overlapping p orbitals form a delocalized pi system above and below the plane, giving aromatic compounds their unique stability.

26. What is the relationship between molecular orbital theory and sigma/pi bonding?

Molecular orbital theory describes bonding in terms of molecular orbitals formed by linear combinations of atomic orbitals. Sigma bonds correspond to molecular orbitals with cylindrical symmetry, while pi bonds correspond to molecular orbitals with a nodal plane containing the internuclear axis.

27. How does a pi bond differ from a sigma bond?

A pi bond is formed by the sideways overlapping of p orbitals, while a sigma bond is formed by head-on overlapping. Pi bonds are generally weaker than sigma bonds and allow for rotation around the bond axis.

28. Why are sigma bonds stronger than pi bonds?

Sigma bonds are stronger because they involve greater orbital overlap along the internuclear axis, resulting in a higher electron density between the nuclei. Pi bonds have less overlap due to their sideways orientation, making them weaker.

29. How many sigma and pi bonds are in a double bond?

A double bond consists of one sigma bond and one pi bond. The sigma bond forms first, followed by the pi bond, which is created by the sideways overlap of p orbitals.

30. Can pi bonds be formed between s orbitals?

No, pi bonds cannot be formed between s orbitals. Pi bonds require sideways overlap, which is only possible with p orbitals or higher.

31. What is the difference between σ and π in chemical notation?

In chemical notation, σ (sigma) represents a sigma bond, while π (pi) represents a pi bond. These symbols are used to describe the type of overlap in molecular orbitals.

32. How do sigma and pi bonds contribute to a molecule's NMR spectrum?

Both sigma and pi bonds influence NMR spectra. Pi bonds, especially in aromatic systems, create ring currents that affect the chemical shifts of nearby protons. The connectivity established by sigma bonds determines coupling patterns. Double bonds also influence chemical shifts due to anisotropic effects.

33. How do sigma and pi bonds influence a molecule's susceptibility to electrophilic or nucleophilic attack?

Pi bonds are often sites for electrophilic attack due to their electron-rich nature. They can also act as nucleophiles in some cases. Sigma bonds generally don't directly participate in these reactions but influence the overall electron distribution and accessibility of reactive sites in the molecule.

34. What is the role of sigma and pi bonds in determining a molecule's HOMO and LUMO?

The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) are often associated with pi bonding and pi antibonding orbitals, respectively, especially in conjugated systems. However, in some molecules, sigma orbitals can also be the HOMO or LUMO, depending on the overall electronic structure.

35. Can you describe the bonding in carbon monoxide (CO) in terms of sigma and pi bonds?

Carbon monoxide has a triple bond consisting of one sigma bond and two pi bonds. The sigma bond forms from sp hybrid orbitals, while the pi bonds form from the overlap of p orbitals. This bonding arrangement contributes to CO's unique properties and reactivity.

36. What is the significance of sigma and pi bonds in photochemical reactions?

Pi bonds are often the primary players in photochemical reactions. They can absorb light energy, promoting electrons to excited states (often pi*), which can lead to various reactions. Sigma bonds typically require higher energy for excitation but can be involved in some photochemical processes.

37. Can you explain the concept of orbital overlap in bond formation?

Orbital overlap occurs when atomic orbitals of two atoms come close enough for their electron wavefunctions to interact. The greater the overlap, the stronger the bond formed. This overlap is the basis for both sigma and pi bond formation.

38. What types of orbitals can form sigma bonds?

Sigma bonds can be formed by the overlap of s-s, s-p, p-p, or even d orbitals, as long as the overlap occurs along the internuclear axis.

39. How does hybridization affect sigma and pi bond formation?

Hybridization affects the number and orientation of orbitals available for bonding. For example, sp2 hybridization leaves one unhybridized p orbital for pi bond formation, while sp3 hybridization uses all valence orbitals for sigma bonds.

40. How does electron delocalization relate to pi bonding?

Electron delocalization often involves pi electrons. In conjugated systems, pi electrons can be spread over multiple atoms, leading to increased stability and unique chemical properties.

41. What is the relationship between bond order and the number of sigma and pi bonds?

Bond order is the sum of sigma and pi bonds between two atoms. A single bond (order 1) has one sigma bond, a double bond (order 2) has one sigma and one pi bond, and a triple bond (order 3) has one sigma and two pi bonds.

42. Can you explain the concept of antibonding orbitals in relation to sigma and pi bonds?

Antibonding orbitals (σ* and π*) are higher energy molecular orbitals that result from out-of-phase combinations of atomic orbitals. Populating these orbitals weakens or breaks bonds. Pi antibonding orbitals are generally lower in energy than sigma antibonding orbitals.

43. What role do sigma and pi bonds play in determining a molecule's reactivity?

Sigma bonds form the backbone of molecules and are less reactive. Pi bonds are more reactive and often serve as sites for addition reactions or electron donation, influencing a molecule's overall reactivity.

44. How do sigma and pi bonds affect the strength of intermolecular forces?

Pi bonds can contribute to stronger intermolecular forces through pi-stacking interactions. Sigma bonds generally don't directly affect intermolecular forces but influence molecular shape, which impacts intermolecular interactions.

45. How does bond length compare between single, double, and triple bonds?

Bond length decreases as the number of bonds increases. Triple bonds (1σ + 2π) are shorter than double bonds (1σ + 1π), which are shorter than single bonds (1σ). This is due to increased electron density between the nuclei.

46. Can you explain the concept of bond resonance in terms of sigma and pi bonds?

Bond resonance involves the delocalization of pi electrons across multiple possible structures. While sigma bonds remain fixed, pi electrons can be represented as distributed among different locations, leading to resonance hybrid structures that better describe the molecule's true nature.

47. How do sigma and pi bonds affect a molecule's polarizability?

Pi bonds generally contribute more to a molecule's polarizability than sigma bonds. This is because pi electrons are more loosely held and can be more easily distorted by an external electric field, leading to induced dipoles.

48. Can you explain how sigma and pi bonds contribute to the colors of organic compounds?

Pi bonds, particularly in conjugated systems, are primarily responsible for the colors of organic compounds. The energy gap between pi and pi* orbitals often corresponds to visible light wavelengths. More extensive conjugation typically results in absorption of longer wavelengths, changing the perceived color.

49. How do sigma and pi bonds influence a molecule's ionization energy?

Pi bonds generally have higher-energy electrons compared to sigma bonds, making them easier to ionize. Molecules with extensive pi systems often have lower ionization energies. However, the overall molecular structure, determined by sigma bonds, also plays a significant role in ionization energy.

50. How do sigma and pi bonds affect a molecule's electron affinity?

Pi bonds often contribute more to a molecule's electron affinity than sigma bonds. The presence of low-lying pi* antibonding orbitals can make a molecule more likely to accept electrons. However, the overall molecular structure, determined by sigma bonds, also influences electron affinity.

51. Can you explain how sigma and pi bonds affect molecular orbital energy diagrams?

In molecular orbital diagrams, sigma bonding orbitals are typically lower in energy than pi bonding orbitals. Pi antibonding orbitals are usually lower in energy than sigma antibonding orbitals. The arrangement and occupancy of these orbitals determine the molecule's overall electronic structure and properties.

52. How do sigma and pi bonds affect a molecule's bond angles and overall geometry?

Sigma bonds largely determine a molecule's basic geometry through the orientation of hybrid orbitals. Pi bonds can influence geometry by enforcing planarity in certain parts of the molecule, as seen in alkenes or aromatic compounds. The interplay between sigma and pi bonding contributes to the overall 3D structure of molecules.

53. Can you describe the concept of antiaromaticity in terms of sigma and pi bonds?

Antiaromaticity occurs in planar, cyclic compounds with 4n pi electrons. While the sigma bonds form the ring structure, the arrangement of pi electrons leads to instability rather than the enhanced stability seen in aromatic compounds. This results in high reactivity and often non-planar geometries to minimize antiaromatic character.

54. How do sigma and pi bonds contribute to the strength of carbon-carbon bonds in different hybridization states?

The strength of carbon-carbon bonds varies with hybridization due to differences in sigma and pi bonding. Triple bonds (sp hybridization) are strongest due to one strong sigma bond and two pi bonds. Double bonds (sp2) are next strongest with one sigma and one pi bond. Single bonds (sp3) are weakest, having only one sigma bond.

55. What is the relationship between sigma and pi bonds and molecular symmetry?

Sigma bonds often contribute to a molecule's overall symmetry through their arrangement in space. Pi bonds can either enhance or reduce symmetry. For example, the pi bond in ethene enforces planarity, increasing symmetry, while pi bonds in substituted alkenes can lead to geometric isomers with different symmetries. In aromatic compounds, pi bonds contribute to high symmetry through electron delocalization.