Difference Between Sigma and Pi Bond in Tabular Form
Introduction to Difference Between Sigma and Pi Bond
The difference between sigma and pi bond is a key concept in chemistry, helping students understand the nature of chemical bonds, molecular shapes, and reactivity. Distinguishing these two types of covalent bonds is essential for mastering organic and inorganic chemistry topics, especially for Class 11 and Class 12 students preparing for their board exams or entrance tests like JEE and NEET. This page breaks down their differences with simple explanations, helpful diagrams, and easy revision tools.
What is the Difference Between Sigma and Pi Bond in Chemistry?
A sigma (σ) bond is a covalent bond formed by the direct, head-on overlap of atomic orbitals, making it strong and allowing free rotation. A pi (π) bond forms by the sideways overlap of parallel p-orbitals, is weaker, and restricts rotational movement. These concepts appear in chapters related to covalent bonds, hybridization, and molecular orbital theory, making them foundational for your chemistry syllabus.
Molecular Formula and Composition
Sigma and pi bonds themselves do not have a molecular formula, as they are types of bonds rather than compounds. However, the composition of a single, double, or triple bond in a molecule involves a combination of sigma and pi bonds. For example, a single bond (like in ethane, C2H6) has only one sigma bond, a double bond (as in ethylene, C2H4) consists of one sigma and one pi bond, and a triple bond (in acetylene, C2H2) contains one sigma and two pi bonds. These are categorized under types of covalent bonding in chemistry.
Preparation and Synthesis Methods
Sigma and pi bonds are not prepared as separate substances, but their formation is observed during the creation of molecules. Sigma bonds typically form first by head-on orbital overlap (s-s, s-p, or p-p), while pi bonds form when unhybridized p orbitals overlap sideways, often after a sigma bond has already formed. During the synthesis of alkenes and alkynes, you can see both sigma and pi bonds established as carbon atoms form multiple bonds with each other.
Physical Properties of Difference Between Sigma and Pi Bond
Physical properties arising from sigma and pi bonds in molecules include bond strength, bond length, molecular geometry, and rotation possibilities around the bond axis. Sigma bonds are stronger, commonly shorter, and allow free rotation (except in cyclic or crowded systems). Pi bonds are weaker and often longer, and restrict rotation due to their parallel electron cloud arrangement above and below the bond axis.
Difference Between Sigma and Pi Bond in Tabular Form
Sigma (σ) bonds form by direct (end-to-end) orbital overlap, are stronger, and allow molecular rotation. Pi (π) bonds form by sideways overlap, are weaker, and restrict rotational movement. See the table below for a concise difference between sigma and pi bond.
| Sigma Bond (σ) | Pi Bond (π) |
|---|---|
| Formed by head-on (axial) overlap of orbitals | Formed by sideways (lateral) overlap of p orbitals |
| Stronger bond due to greater overlapping | Weaker bond due to less overlapping |
| Allows free rotation around bond axis | Restricts rotation around bond axis |
| Electron density is maximum along the bond axis (cylindrical symmetry) | Electron density is above and below the bond axis (no cylindrical symmetry) |
| Can be formed by overlapping of s-s, s-p, or p-p orbitals (hybrid or pure) | Only formed by overlap of unhybridized p orbitals (pure p-p) |
| Present singly (single bond) or as part of double/triple bonds | Only found with a sigma bond in double or triple bonds |
| Determines molecular shape | Does not influence molecular shape |
| Example: C–H bond in CH4, H–H bond in H2 | Example: C=C in C2H4, C≡C in C2H2 |
Step-by-Step Reaction Example
1. Consider ethylene (C2H4) molecule.2. Each carbon forms three sigma bonds (two with hydrogen, one with other carbon) using sp2 hybrid orbitals.
3. Unhybridized p orbitals on each carbon overlap sideways to form a pi bond above and below the internuclear axis.
4. Final Answer: Ethylene contains one sigma bond and one pi bond between carbons.
Frequent Related Errors
- Assuming double bond means two sigma bonds or triple bond means three sigma bonds – Actually, double bond = 1 sigma + 1 pi; triple bond = 1 sigma + 2 pi.
- Ignoring pi bonds in the discussion of molecular shape – only sigma bonds affect overall shape.
- Confusing sideways overlap (pi) with head-on overlap (sigma) in reaction mechanisms.
- Forgetting that only pure, unhybridized p orbitals form pi bonds.
Uses of Difference Between Sigma and Pi Bond in Real Life
Understanding the difference between sigma and pi bond allows chemists to predict molecular reactivity, explain shapes of organic and inorganic molecules, and develop new materials. Applications include the design of polymers, medicines, plastics, and even in understanding biological molecules such as proteins and DNA which contain double and triple bonds. This knowledge is essential in organic synthesis, material science, and industrial chemistry.
Relevance in Competitive Exams
Students preparing for exams like NEET, JEE, and Olympiads are often asked about the difference between sigma and pi bond in both MCQ and descriptive formats. They may be asked to count sigma and pi bonds in molecules, or explain bond rotation and reactivity differences. Mastery of this topic boosts your performance in all chemistry-based competitive exams.
Relation with Other Chemistry Concepts
Sigma and pi bonds are closely related to topics like covalent hydrides, hybridization, Lewis dot structures, and molecular orbitals. Together, they help make sense of electron distribution, bond energy, and molecular geometry in all branches of chemistry.
Lab or Experimental Tips
Remember: "Single bond = 1 sigma, Double bond = 1 sigma + 1 pi, Triple bond = 1 sigma + 2 pi." Use colored molecular models to represent sigma and pi bonds during classroom experiments. Vedantu educators frequently show these visualizations in live sessions for better concept clarity.
Try This Yourself
- Count the number of sigma and pi bonds in benzene (C6H6).
- Draw electron cloud diagrams to show sigma and pi bonding in ethyne (C2H2).
- Identify which type of bond breaks first during hydrogenation of alkenes (pi or sigma?).
- Sketch a table comparing sigma and pi bonds based on formation and properties.
Final Wrap-Up
We explored the difference between sigma and pi bond—their formation, strength, orientation, examples, and importance in chemistry. For in-depth diagrams, exam-focused notes, and live interactive learning, visit Vedantu’s platform. Mastering this topic will strengthen your understanding of bonding and boost your chemistry scores!
Explore related concepts:
Pi Bonds |
Hybridization |
Lewis Dot Structures |
Chemical Bonding and Molecular Structure |
Molecular Orbitals of H2 and He2
FAQs on Difference Between Sigma and Pi Bond
1. What is the main difference between sigma and pi bonds?
The primary difference lies in how the atomic orbitals overlap. A sigma (σ) bond forms through direct, head-on overlap of atomic orbitals, resulting in a strong bond with cylindrical symmetry around the bond axis. A pi (π) bond, however, forms through sideways overlap of p-orbitals, creating a weaker bond with electron density above and below the bond axis. This difference in overlap significantly impacts bond strength and rotational freedom.
2. Why is a sigma bond stronger than a pi bond?
A sigma bond is stronger because the head-on overlap of atomic orbitals leads to greater electron density concentrated directly between the two bonded nuclei. This results in a stronger electrostatic attraction between the nuclei and the shared electrons. In contrast, the sideways overlap in a pi bond results in less electron density directly between the nuclei, leading to a weaker bond.
3. Give one example each of a sigma bond and a pi bond.
A sigma bond is found in every single bond, such as the C-H bonds in methane (CH4). A pi bond is found in double and triple bonds; for example, the C=C double bond in ethene (C2H4) contains one sigma and one pi bond.
4. How are sigma and pi bonds formed in molecules?
Sigma (σ) bonds are formed by the direct, end-to-end overlap of atomic orbitals (s-s, s-p, or p-p). Pi (π) bonds are formed by the sideways overlap of two parallel p-orbitals. A double bond consists of one sigma and one pi bond, while a triple bond comprises one sigma and two pi bonds.
5. How many sigma and pi bonds are there in ethylene (C2H4)?
Ethylene (C2H4) has five sigma (σ) bonds and one pi (π) bond. Each C-H bond is a sigma bond, the C-C bond is a sigma bond, and the second bond in the C=C double bond is a pi bond.
6. Can a pi bond form before a sigma bond between two atoms?
No, a sigma bond must always form first. The formation of a pi bond requires the presence of a pre-existing sigma bond. Pi bonds form only after sigma bonds are established between the atoms.
7. Are sigma and pi bonds present in all types of double or triple bonds?
Yes, all double bonds contain one sigma (σ) bond and one pi (π) bond. All triple bonds contain one sigma (σ) bond and two pi (π) bonds. The sigma bond is always formed first, providing the framework for the subsequent pi bond formation.
8. What happens to the molecular geometry if only pi bonds are present?
Pi bonds alone cannot determine molecular geometry. Pi bonds always accompany sigma bonds. The presence of only pi bonds is not a physically possible scenario in stable molecules.
9. How does hybridization influence the presence of sigma and pi bonds?
Hybridization affects the number and types of bonds an atom can form. For example, sp3 hybridized carbon forms only sigma bonds, while sp2 hybridized carbon forms one pi bond in addition to its sigma bonds, and sp hybridized carbon forms two pi bonds in addition to one sigma bond. The type of hybridization dictates the orbital availability for both sigma and pi bond formation.
10. What are delta (δ) bonds, and how do they compare to sigma and pi bonds?
Delta (δ) bonds are a type of covalent bond formed by the interaction of four lobes of d-orbitals. They are even weaker than pi bonds and are less common than sigma and pi bonds. They are found in some transition metal complexes. They are formed after sigma and pi bonds are already present.
11. Explain the difference in bond rotation between sigma and pi bonds.
Sigma (σ) bonds allow free rotation around the bond axis. Pi (π) bonds restrict rotation around the bond axis because rotation would disrupt the sideways overlap of the p-orbitals, breaking the pi bond.
12. What is the relationship between bond order and the number of sigma and pi bonds?
Bond order is the number of chemical bonds between a pair of atoms. A single bond has a bond order of 1 (one sigma bond), a double bond has a bond order of 2 (one sigma and one pi bond), and a triple bond has a bond order of 3 (one sigma and two pi bonds). The bond order indicates the strength of the bond between two atoms.
