Question

How many electron pairs are shared when a triple bond exists between two carbon atoms? What must be the geometric arrangement around the carbon atoms in a triple bond? Draw the Lewis structure of a simple molecule that contains a triple bond.

Short answer

Three electron pairs are shared in a triple bond between two carbon atoms. The geometric arrangement around the carbon atoms in a triple bond is linear, with a bond angle of 180 degrees due to sp-hybridization. The Lewis structure of a simple molecule containing a triple bond, such as ethyne (C2H2), is: H \ C ≡ C / H

Step-by-step solution

Determine the number of electron pairs shared in a triple bond

Triple bonds consist of three shared electron pairs. In a triple bond, one pair of electrons forms a sigma bond, while the other two pairs of electrons form pi bonds.

Describe the geometric arrangement around the carbon atoms in a triple bond

In a triple bond, the two carbon atoms and the atoms they are bonded with are located in the same straight line. That is because the carbon atoms are sp-hybridized, which results in linear geometry with a bond angle of 180 degrees.

Draw the Lewis structure of a simple molecule that contains a triple bond

A simple molecule containing a triple bond between two carbon atoms is ethyne, C2H2. Drawing its Lewis structure: 1. Calculate the total number of valence electrons in the molecule. Carbon (C) has 4 valence electrons, and hydrogen (H) has 1 valence electron. Therefore, for two carbon atoms and two hydrogen atoms, the total number of valence electrons is (2 × 4) + (2 × 1) = 10 electrons. 2. Connect the two carbon atoms with a triple bond, which represents six electrons (three electron pairs). 3. Add hydrogen atoms to the carbon atoms and connect each hydrogen atom to the carbon atoms using single bonds, representing two more valence electrons. 4. Count the total number of electrons and check if it matches the actual number of valence electrons (in this case, 10 electrons). Here is the Lewis structure of ethyne (C2H2): H \ C ≡ C / H In the ethyne molecule, the two carbon atoms form a triple bond with three shared electron pairs, and each carbon atom is bonded with one hydrogen atom. The geometric arrangement around the carbon atoms is linear with a bond angle of 180 degrees.

Key concepts

Electron Pairs

Electron pairs are crucial in understanding chemical bonding. When atoms form bonds, they share or transfer electron pairs to attain stable electronic configurations. In a triple bond, three pairs of electrons are shared between atoms. This means six electrons in total are shared between the two atoms participating in the triple bond.
In organic chemistry, carbon atoms commonly form triple bonds with each other. In such bonds, one pair of electrons is used to form a sigma bond, which is the strongest type of covalent bond. Then, the other two pairs form pi bonds, which are parallel to each other. Pi bonds are generally weaker than sigma bonds, but provide the additional stability and strength needed for a triple bond.

Notably, this arrangement directly influences the molecule's geometry and properties, as we will discuss further in this article.

Lewis Structure

A Lewis structure is a simplified way to represent the valence electrons in a molecule. Valence electrons are depicted as dots around the atomic symbols, and lines between atoms indicate shared pairs of electrons, or bonds.
The purpose of drawing a Lewis structure is to visualize how electrons are distributed in a molecule and to predict the arrangement of atoms. In the case of ethyne (\( \text{C}_2\text{H}_2 \)), the Lewis structure is instrumental in showing the triple bond between the two carbon atoms, representing three shared electron pairs.

Each carbon atom is bonded to one hydrogen atom, shown with a single line, representing a single bond. The triple bond between carbon atoms is depicted with three lines. This visual aid helps students better understand the molecular structure, electron sharing, and configuration.

Hybridization

Hybridization is a concept in chemistry where atomic orbitals mix to create new, hybrid orbitals. These are suitable for pairing electrons to form chemical bonds. For carbon atoms involved in a triple bond, the hybridization is sp.

In sp hybridization, one 's' orbital and one 'p' orbital combine to form two equivalent sp hybrid orbitals. The remaining two 'p' orbitals stay unhybridized and form the two pi bonds of the triple bond. The sp hybrid orbitals form one sigma bond between the two carbon atoms.

This sp hybridization gives the molecule a linear shape, as the hybrid orbitals are arranged 180 degrees apart, leading to a clear, straight line geometry. This linearity is evident in the structure of ethyne, where both carbon atoms, being sp hybridized, align in one straight line with their respective atoms.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are key in determining how atoms interact during the formation of chemical bonds. For carbon, there are 4 valence electrons, whereas hydrogen possesses just 1 valence electron.

When constructing a Lewis structure, it's important to first count the total valence electrons available for the entire molecule. In ethyne (\( \text{C}_2\text{H}_2 \)), we have a total of 10 valence electrons: 8 from the two carbon atoms (2 x 4) and 2 from the hydrogen atoms (2 x 1). These electrons are used in forming the triple bond (6 electrons) and the two single bonds (2 electrons each) with hydrogens.

Understanding valence electrons helps in accurately predicting how atoms will bond, ensuring the correct distribution of electron pairs, and therefore, achieving stable molecular structures.