Short Answer

Multiple bonds are chemical bonds in which two atoms share more than one pair of electrons. Instead of sharing just one pair (a single bond), they may share two pairs (a double bond) or three pairs (a triple bond). These bonds create stronger and shorter connections between atoms compared to single bonds.

Multiple bonds commonly occur in molecules like oxygen (O₂), carbon dioxide (CO₂), nitrogen (N₂), and ethene (C₂H₄). They play an important role in determining the shape, reactivity, and strength of molecules in organic and inorganic chemistry.

Detailed Explanation :

Multiple Bonds

Multiple bonds are chemical connections where two atoms share more than one pair of electrons. These bonds form when atoms need additional shared electrons to complete their valence shells and become stable. While a single bond involves the sharing of one electron pair, multiple bonds involve two or three shared pairs, leading to double bonds and triple bonds, respectively.

Multiple bonds are essential in chemistry because they influence many properties of molecules, including their geometry, strength, and reactivity. They are especially common in carbon-based molecules, which form the backbone of organic chemistry.

1. Types of Multiple Bonds

There are two main types of multiple bonds:

1. a) Double Bonds

A double bond contains two shared pairs of electrons between two atoms.

Examples:

• O₂ has a double bond between two oxygen atoms
• CO₂ contains two C=O double bonds
• Ethene (C₂H₄) has a C=C double bond

Characteristics of double bonds:

• Stronger than single bonds
• Shorter bond length
• Restricted rotation around the bond
• One sigma (σ) bond + one pi (π) bond

1. b) Triple Bonds

A triple bond contains three shared electron pairs between two atoms.

Examples:

• Nitrogen gas (N₂) has a strong N≡N triple bond
• Acetylene (C₂H₂) has a C≡C triple bond

Characteristics of triple bonds:

• Stronger and shorter than both single and double bonds
• Even more restricted rotation
• One sigma (σ) bond + two pi (π) bonds

These features give triple-bonded molecules unique properties, such as high bond energy and lower bond length.

2. Sigma and Pi Bonds in Multiple Bonding

Multiple bonds always consist of:

• One sigma bond → formed by head-on overlap of orbitals
• One or two pi bonds → formed by sideways overlap of p orbitals

A double bond = 1 sigma + 1 pi
A triple bond = 1 sigma + 2 pi

The presence of pi bonds is what restricts rotation, because breaking rotation would require breaking the pi bond first.

3. Formation of Multiple Bonds

Multiple bonds form when:

• Atoms need more electrons to complete their octet
• Sharing only one pair is not enough
• Overlapping orbitals allow for additional electron sharing

For example:

• Carbon needs four electrons to complete its octet
• In ethene (C₂H₄), each carbon forms three sigma bonds and one pi bond to achieve stability
• In nitrogen (N₂), each nitrogen shares three pairs to complete its octet

Multiple bonding allows atoms to meet the electron requirements needed for stability.

4. Properties of Multiple Bonds

Multiple bonds cause significant changes in a molecule’s characteristics:

1. i) Bond Strength

Triple bond > Double bond > Single bond
More shared electrons = stronger bond.

1. ii) Bond Length

Triple bonds are shortest, followed by double, then single.

iii) Reactivity

Multiple bonds are more reactive because:

• Pi bonds are weaker and break easily
• Electrons in pi bonds are exposed and can participate in reactions

This is why alkenes and alkynes are more reactive than alkanes.

1. iv) Molecular Shape

Multiple bonds affect geometry:

• Double-bonded atoms tend to form planar structures
• Triple-bonded atoms form linear shapes

For example:

• Ethene is planar due to sp² hybridization
• Acetylene is linear due to sp hybridization

5. Importance of Multiple Bonds in Chemistry

Multiple bonds play key roles in:

• Organic chemistry (alkenes, alkynes, aromatic compounds)
• Biology (structure of proteins and DNA bases)
• Industrial chemistry (polymer formation)
• Atmospheric chemistry (O₂ and N₂ stability)

They also help determine physical properties like melting point, boiling point, and solubility.

Without multiple bonding, complex molecules that sustain life would not form.

Conclusion

Multiple bonds are chemical connections where two atoms share two or three pairs of electrons, forming double or triple bonds. These bonds contain one sigma bond and one or more pi bonds, making them shorter, stronger, and more rigid than single bonds. Multiple bonds significantly influence molecular structure, reactivity, and stability, making them essential for understanding chemical bonding and molecular behavior.