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9.4.2 - Structure of Triple Bond

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Understanding Triple Bonds

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Teacher
Teacher

Today, we’re going to discuss the structure of triple bonds, specifically focusing on ethyne. Who can tell me what a triple bond consists of?

Student 1
Student 1

A triple bond consists of one sigma bond and two pi bonds, right?

Teacher
Teacher

Exactly! The sigma bond is formed by head-on overlap of sp hybrid orbitals from each carbon. That’s how ethyne forms its structure. Can anyone tell me what the bond angle is in ethyne?

Student 2
Student 2

I think it’s 180 degrees?

Teacher
Teacher

You've got it! Ethyne has a linear configuration, resulting in a 180° bond angle. Remember that’s due to the sp hybridization.

Student 3
Student 3

So, the orientation of the bonds in ethyne is what makes it linear?

Teacher
Teacher

Yes! The sp hybridization also allows for the formation of those two pi bonds. Let’s remember this with the acronym 'SP' for ‘Strong Pi’ when thinking of how they stabilize and make the molecule strong.

Student 4
Student 4

That’s a good memory aid! What about the bond enthalpy and lengths?

Teacher
Teacher

Great question! The bond enthalpy for the C≡C bond is 823 kJ/mol, and it's shorter than both C=C and C–C bonds.

Teacher
Teacher

In summary, a triple bond consists of one sigma bond and two pi bonds, the bond angle is 180°, and ethyne illustrates the unique strength and orientation of these bonds effectively.

Properties of Ethyne

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Teacher
Teacher

Now that we understand the structure of ethyne, let’s talk about its properties. Why do you think the strength of the C≡C bond is so significant?

Student 1
Student 1

Is it because it makes alkyne compounds very reactive?

Teacher
Teacher

Yes! The high bond strength provides stability, but the presence of two pi bonds makes alkynes reactive towards addition reactions. Can anyone think of an example of a reaction involving ethyne?

Student 2
Student 2

It can react with hydrogen to form ethane, right?

Teacher
Teacher

Correct! Ethyne reacts with hydrogen in the presence of a catalyst to undergo hydrogenation, resulting in ethane. Always remember that it’s these reactions that reflect the nature of triple bonds and their versatility.

Student 3
Student 3

So, aside from being strong, what other properties are characteristic of ethyne?

Teacher
Teacher

Ethyne is colorless and has a distinct odor. But more importantly, it is less soluble in water compared to hydrocarbons with only single or double bonds. Let’s keep that in mind when thinking about its uses.

Teacher
Teacher

To sum up, ethyne's triple bond results in strong stability, characteristic reactions, and distinct physical properties.

Reviewing Hybridization

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Teacher
Teacher

We have talked about ethyne and its structure. Let's review hybridization. What type of hybridization does carbon undergo in alkynes?

Student 4
Student 4

It’s sp hybridization for triple bonds.

Teacher
Teacher

Right! This defines how the bonds are arranged and contributes to the characteristics of the molecule. What does ‘sp’ hybridization mean in terms of orbital overlaps?

Student 1
Student 1

It means two of the carbon’s atomic orbitals combine to form two equivalent sp hybrid orbitals.

Teacher
Teacher

Precisely. And these combine to form strong sigma bonds while the other unhybridized p orbitals form the pi bonds we discussed earlier.

Student 2
Student 2

Can you remind us how these structures affect the properties of alkynes?

Teacher
Teacher

Of course! Since the unshared p orbitals create lateral overlaps forming pi bonds, this not only leads to strength but also makes them reactive. Remember this relationship between structure and reactivity in organic compounds.

Teacher
Teacher

To conclude, the hybridization of carbon directly impacts bond formation, molecular shape, and the reactivity of alkynes.

Introduction & Overview

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Quick Overview

This section explains the structural aspects and bonding characteristics of triple bonds in alkynes, specifically focusing on ethyne.

Standard

The structure of ethyne is dissected to illustrate the formation and characteristics of the triple bond. The hybridization states of carbon, the arrangement of electrons, and bond lengths are highlighted, showcasing the inherent properties of alkynes.

Detailed

Structure of Triple Bond

The simplest alkyne, ethyne (C₂H₂), reveals the distinct structural characteristics associated with triple bonds in alkynes. Each carbon atom in ethyne employs sp hybridization, forming two sp hybrid orbitals used for the creation of sigma (σ) bonds. These σ bonds arise from the head-on overlapping of these orbitals, contributing to the formation of a linear configuration with a bond angle of 180°.

Additionally, each carbon atom retains two unhybridised p orbitals, which are oriented perpendicularly to the plane of the C-C sigma bond. These p orbitals allow for lateral overlapping between the two carbon atoms, resulting in the formation of two pi (π) bonds. This characteristic bonding configuration indicates that an ethyne molecule consists of one C–C σ bond, two C–H σ bonds, and two C–C π bonds.

The strength of the C≡C bond is significant, with a bond enthalpy of 823 kJ/mol, which is greater than that of double (C=C) and single (C–C) bonds. Furthermore, the bond length of the C≡C bond is shorter (120 pm) compared to C=C (133 pm) and C–C (154 pm). This analysis of the ethyne molecule encapsulates the defining attributes of triple bonds in alkynes and emphasizes their unique chemical properties in comparisons with alkenes and alkanes.

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Audio Book

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Introduction to Ethyne Structure

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Ethyne is the simplest molecule of alkyne series. Structure of ethyne is shown in Fig. 9.6.

Detailed Explanation

Ethyne, which is also commonly known as acetylene, serves as the fundamental structure in the alkyne series. It's key to understand that the molecular structure of ethyne is a representation of how carbon atoms bond with one another. In this case, the two carbon atoms are linked by a triple bond, representing a strong connection between them.

Examples & Analogies

Think of ethyne like two friends, tightly holding each other’s hands in a playful tug-of-war, where they can’t let go easily. This unique bond, the triple bond, makes them strongly connected and stable, similar to how acetylene is used in welding due to its strong and stable composition.

Bonding in Ethyne

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Each carbon atom of ethyne has two sp hybridised orbitals. Carbon-carbon sigma (σ) bond is obtained by the head-on overlapping of the two sp hybridised orbitals of the two carbon atoms. The remaining sp hybridised orbital of each carbon atom undergoes overlapping along the internuclear axis with the 1s orbital of each of the two hydrogen atoms forming two C-H sigma bonds.

Detailed Explanation

In ethyne, carbon is hybridized into an sp configuration, meaning one s orbital and one p orbital combined to form two equivalent sp orbitals. These sp hybridized orbitals are arranged linearly (180° apart) to form a sigma bond between the two carbon atoms. The remaining sp orbital on each carbon, meanwhile, overlaps with the 1s orbital of hydrogen to create C-H sigma bonds, establishing a stable molecular structure.

Examples & Analogies

Imagine a tightrope walker (the carbon atoms) using a long rod (the sigma bond) for balance, while cheering fans (the hydrogen atoms) are lined up along the edge, each holding onto the rope tightly. This captures the relationship between carbon and hydrogen in ethyne: balanced, strong, and secure.

Angle and Unhybridized Orbitals

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H-C-C bond angle is of 180°. Each carbon has two unhybridised p orbitals which are perpendicular to each other as well as to the plane of the C-C sigma bond.

Detailed Explanation

In ethyne, the bond angle between the carbon and hydrogen (H-C-C) is exactly 180°. This linear arrangement is characteristic of sp hybridization. The two carbon atoms also have unhybridized p orbitals, which sit perpendicular to each other and the sigma bond, allowing them to participate in the formation of pi bonds.

Examples & Analogies

Consider a pair of tall towers standing straight up, representing the carbon atoms in ethyne. The angle between the towers is perfectly flat, representing the linear bond angle of 180°. The clouds (the unhybridized p orbitals) float above and on the side of the towers, showing how they can form additional bonds even while keeping their structure intact.

Formation of Pi Bonds

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The 2p orbitals of one carbon atom are parallel to the 2p orbitals of the other carbon atom, which undergo lateral or sideways overlapping to form two pi (π) bonds between two carbon atoms.

Detailed Explanation

In ethyne, the two unhybridized p orbitals of adjacent carbon atoms overlap side-to-side, forming two pi bonds. These pi bonds, together with the sigma bond, form a triple bond between the carbon atoms, which makes ethyne very different from alkenes, which feature only one pi bond.

Examples & Analogies

Imagine two hula-hoop performers standing next to each other, holding their hoops parallel, and then interlocking them sideways. This interaction gives their performance (the triple bond) stability and strength, much like the way pi bonds add to the overall bond strength in ethyne.

Bond Strength and Length

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Thus ethyne molecule consists of one C–C σ bond, two C–H σ bonds and two C–C π bonds. The strength of C≡ C bond (bond enthalpy 823 kJ mol-1) is more than those of C=C bond (bond enthalpy 681 kJ mol–1) and C–C bond (bond enthalpy 348 kJ mol–1). The C≡ C bond length is shorter (120 pm) than those of C=C (133 pm) and C–C (154 pm).

Detailed Explanation

The structure of ethyne reveals that it has a C-C bond characterized by very strong triple bond comprising one sigma and two pi bonds. Bonds are quantified in terms of bond enthalpy—the higher the enthalpy, the stronger the bond. Moreover, the C≡C bond is shorter than C=C and C-C bonds due to the additional bonding interactions.

Examples & Analogies

Think of the C-C bonds in ethyne as tightly woven fabric, where each thread contributes to the overall strength and tightness. The more threads (bonds) you have, the stronger and shorter the fabric becomes, making it less prone to tearing apart.

Molecular Geometry

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Thus, ethyne is a linear molecule.

Detailed Explanation

Given the hybridization and bond angles present in ethyne, the molecule adopts a linear geometry. This means that its physical presence in space is a straight line, fundamentally affecting how it interacts with other molecules.

Examples & Analogies

Visualize a simple straw: it's a straight path allowing air to pass through easily, just like ethyne's linear structure allows smooth reactions and interactions with other chemicals.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Structure of Triple Bond: Composed of one sigma bond and two pi bonds.

  • Hybridization: sp hybridization is involved in the formation of triple bonds.

  • Properties of Ethyne: Shorter bond length and higher bond enthalpy than single and double bonds.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Ethyne (C2H2) illustrates a triple bond with one sigma and two pi bonds.

  • The importance of ethyne in industrial applications such as welding.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Triple bonds are strong and fine, one sigma, two pi, it's all in line.

📖 Fascinating Stories

  • Imagine the carbon atoms in ethyne as two friends holding hands (sigma bond) and hugging (pi bonds) tightly, making their bond strong and unbreakable.

🧠 Other Memory Gems

  • S-P-P structure for the triple bond in ethyne - one S is sigma, and two P's are pi.

🎯 Super Acronyms

C-C-180

  • Two carbons with a bond angle of 180 degrees for ethyne.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Triple Bond

    Definition:

    A bond between two atoms involving three pairs of shared electrons.

  • Term: Sigma Bond (σ bond)

    Definition:

    A type of covalent bond formed by the head-on overlap of atomic orbitals.

  • Term: Pi Bond (π bond)

    Definition:

    A type of covalent bond formed by the side-by-side overlap of p orbitals.

  • Term: Hybridization

    Definition:

    The grouping of atomic orbitals to form new hybrid orbitals for bonding.