Question

Compare single, double, and triple bonds in a molecule, and give an example of each. For the same bonding atoms, how does the bond length change from single bond to triple bond?

Short answer

Bond length decreases from single to triple bonds: single > double > triple.

Step-by-step solution

Understand the Types of Bonds

In chemistry, bonds between atoms can be single, double, or triple. A single bond involves the sharing of one pair of electrons, a double bond involves two pairs, and a triple bond involves three pairs of electrons between two atoms.

Example of Single, Double, and Triple Bonds

An example of a single bond is hydrogen gas (H₂), where two hydrogen atoms share a single pair of electrons. Ethylene (C₂H₄) is an example of a molecule with a carbon-carbon double bond. Acetylene (C₂H₂) is an example with a carbon-carbon triple bond.

Analyze the Bond Lengths

As more electron pairs are shared, bonds become shorter and stronger. Thus, a single bond is longest, a double bond is shorter, and a triple bond is shortest due to increased electron sharing.

Observation of Bond Length

For the same type of atoms, such as carbon-carbon, the bond length decreases in the order: single bond > double bond > triple bond. This means the triple bond is the shortest, and the single bond is the longest.

Key concepts

Single Bond

In the world of chemistry, understanding the basic concept of a single bond is fundamental. A single bond is the simplest type of chemical bond and involves the sharing of one pair of electrons between two atoms.
In this bonding scenario, each atom contributes one electron to form a shared pair, symbolized by a single line in structural formulas.
Common examples of single bonds can be found in molecules like hydrogen gas (H₂), where two hydrogen atoms join by sharing one pair of electrons.
Simple and stable, single bonds are essential for forming many molecular structures, though they are relatively longer and weaker compared to other bond types.

Double Bond

Double bonds are characterized by the sharing of two pairs of electrons between two atoms. This type of bond is stronger and shorter than a single bond due to the increased number of shared electrons.
Double bonds are often found in molecules where more stability is required, enhancing their structural integrity.

• Ethylene (C₂H₄) is a perfect example of a molecule with a double bond.
• In ethylene, each carbon atom shares two pairs of electrons with another carbon atom, depicted as two lines in chemical structures.

The presence of a double bond affects the molecule's geometry, often leading to a planar arrangement to accommodate the extra bonding.

Triple Bond

Triple bonds involve sharing three pairs of electrons between two atoms. This is the strongest type of covalent bond due to its maximum electron sharing capacity and also the shortest in terms of bond length.
With three shared pairs, the bond is depicted by three parallel lines in chemical diagrams, showing its formidable strength.
A standard example of a molecule with a triple bond is acetylene (C₂H₂).

• In acetylene, each carbon atom shares three pairs of electrons with the adjacent carbon.

The robust nature of triple bonds makes them critical in compounds requiring great stability and reduced bond lengths.

Bond Length

Bond length is the distance between the nuclei of two bonded atoms. It changes with the type of bond due to the variation in electron sharing quantities.
In general, as the number of shared electron pairs increases, the bond length decreases:

• A single bond, involving one shared pair, is the longest.
• A double bond, with two pairs, is shorter than a single bond.
• And a triple bond, sharing three pairs of electrons, is the shortest.

This relationship arises because additional electron sharing increases the attraction between atoms, pulling them closer together.

Electron Sharing

Electron sharing is the core principle behind covalent bonding, where atoms achieve stability by sharing their outer electrons.
The extent of electron sharing defines the type and strength of the bond.
For instance, a single pair corresponds to a single bond, two pairs to a double bond, and three pairs to a triple bond.

• More extensive sharing, such as in double and triple bonds, translates to stronger bonds.
• The concept highlights how atoms seek to complete their electron shells, mirroring the stability of noble gases.

The strategy of electron sharing helps explain the variety and functionality of molecular structures in chemistry.