Question

What does a triple bond represent? How many pairs of electrons are shared between the atoms in a triple bond? Draw the Lewis structure of a molecule with a triple bond.

Short answer

A triple bond represents a type of covalent bond where three pairs of electrons are shared between two atoms, resulting in a stronger and shorter bond compared to single or double bonds. In a triple bond, six electrons (3 pairs) are involved. In ethyne (C2H2) molecule, there's a triple bond between two carbon atoms. Its Lewis structure can be represented as H-C≡C-H, where C≡C indicates the triple bond and single lines (-) depict single bonds between carbon and hydrogen atoms.

Step-by-step solution

Understand and describe a triple bond

A triple bond is a type of covalent bond that involves the sharing of three pairs of electrons between two atoms. This bond is the result of an overlapping between the orbitals of the two bonding atoms, and it is formed to achieve stability and a lower energy state by filling their respective valence electron shells. Triple bonds are stronger and shorter than single and double bonds because they involve a greater number of shared electron pairs.

Determine the number of electron pairs shared in a triple bond

In a triple bond, three pairs of electrons are shared between the two bonding atoms. Thus, a total of six electrons (3 pairs) are involved in the formation of a triple bond.

Choose a molecule with a triple bond for the Lewis structure

Let us choose a molecule with a triple bond to draw its Lewis structure. In this case, we will consider ethyne (also known as acetylene), a hydrocarbon with the molecular formula \(C_2H_2\). Ethyne consists of two carbon atoms connected by a triple bond and one hydrogen atom bonded to each carbon atom with a single bond.

Draw the Lewis structure for ethyne (C2H2)

To draw the Lewis structure of ethyne, follow these steps: 1. Identify the central atoms: In ethyne, the central atoms are the two carbon atoms. 2. Count the total number of valence electrons: Carbon belongs to group 4A, so it has 4 valence electrons. Hydrogen has 1 valence electron since it belongs to group 1A. So, for ethyne, the total number of valence electrons is: Total valence electrons = (2 C atoms × 4 e⁻/atom) + (2 H atoms × 1 e⁻/atom) = 8 + 2 = 10 valence electrons. 3. Use these electrons to form bonds and complete the octet rule for carbon atoms and duet rule for hydrogen atoms: a) Place a single bond between each carbon and hydrogen atom (a single bond consists of two shared electrons). b) Place a triple bond between the two carbon atoms (a triple bond consists of six shared electrons). 4. The final Lewis structure for ethyne should display the following: - A triple bond between the two carbon atoms, - A single bond between each carbon atom and a hydrogen atom. The completed Lewis structure for ethyne (C2H2) can be represented as: H-C≡C-H Here, C≡C represents the triple bond between the two carbon atoms, and the single bond between each carbon and hydrogen atom is represented by a single line (-).

Key concepts

Covalent Bond

A covalent bond is a fundamental concept in chemistry where two atoms share electrons to achieve stability in their outer electron shells. This type of bond usually forms between non-metal atoms, allowing them to fill their outermost electron shells. This process results in a lower energy state for the atoms, making the molecules more stable. Multiple covalent bonds can occur between atoms, such as single, double, or triple bonds, depending on the number of electron pairs shared. ### Characteristics of Covalent Bonds:

• **Directionality**: Covalent bonds are directional, meaning the bond has a specific orientation in space, leading to the molecule's shape.
• **Strength**: Typically, covalent bonds are quite strong, especially compared to ionic bonds. Triple bonds are even stronger than single and double bonds.
• **Locality**: These bonds generally affect only the immediate atoms involved, influencing molecular geometry.

Lewis Structure

The Lewis structure, also known as the Lewis dot structure, is a way of representing molecules. It shows the arrangement of atoms within a molecule and how they are bonded together. It is particularly useful in visualizing the sharing of electrons between atoms in covalent bonds. ### Constructing a Lewis Structure:

• **Count Electrons**: First, you count the total number of valence electrons from all the atoms in the molecule.
• **Organize Atoms**: Determine which atoms are the core and which are terminal. Central atoms are typically less electronegative.
• **Distribute Electrons**: Place pairs of electrons between atoms to form bonds and around the outer atoms to satisfy the octet rule (or duet for hydrogen).

When considering a triple bond, such as in a molecule like ethyne ( C_2H_2 ), the Lewis structure is specifically important. It helps illustrate the triple bond as three pairs of dots (or lines) between the atoms, signifying the sharing of three pairs of electrons.

Electron Sharing

Electron sharing is a key concept in covalent bonding where atoms share one or more pairs of electrons. This sharing allows each atom to fill its valence shell to achieve a more stable electronic configuration. ### How Electron Sharing Works:

• **Single Bonds**: One pair of electrons is shared between two atoms.
• **Double Bonds**: Two pairs of electrons are shared, making the bond stronger and shorter than a single bond.
• **Triple Bonds**: Three pairs of electrons are shared, resulting in even stronger and shorter bonds compared to both single and double bonds.

In a triple bond, like in ethyne, three pairs of electrons are shared between the two carbon atoms. This extensive electron sharing not only strengthens the bond but also shortens the distance between the two atoms.

Stability in Molecules

The concept of stability in molecules is closely related to how the atoms are bonded within them. When atoms share electrons through covalent bonds, they achieve a stable electronic configuration, often matching that of the nearest noble gas. ### Factors Influencing Stability:

• **Electron Configuration**: Molecules with full valence electron shells are at their most stable state.
• **Bond Length and Strength**: Stronger and shorter bonds, such as triple bonds, contribute to the molecule's overall stability.
• **Molecular Shape and Symmetry**: The spatial arrangement can further influence the energy state and stability.

In a molecule like ethyne, the triple bond between the carbon atoms provides significant stability. This is due to the maximal electron sharing, which effectively lowers the energy and contributes to a very stable configuration.