What is a double bond ?

Answer

**Step-by-Step Solution:**

1. **Definition of Double Bond:**
A double bond is a type of chemical bond that involves the sharing of two pairs of electrons between two atoms. It is represented by two lines between the symbols of the bonded atoms.

2. **Formation of Double Bond:**
A double bond is formed through two types of overlapping:
- **Head-to-Head Overlapping:** This type of overlap occurs when the atomic orbitals of the bonding atoms align directly along the axis connecting the two nuclei. This overlap forms a **sigma (σ) bond**.
- **Sidewise Overlapping:** This occurs when the atomic orbitals overlap sideways. This type of overlap forms a **pi (π) bond**.

3. **Example of Double Bond:**
Consider the molecule **C2H4 (Ethylene)**. In this molecule, there are two carbon atoms connected by a double bond. Each carbon atom contributes one sigma bond and one pi bond to form the double bond.

4. **Orbital Representation:**
- Each carbon atom has a **p orbital** that contains one unpaired electron.
- When the two carbon atoms approach each other, one electron from each carbon atom pairs up to form the sigma bond through head-to-head overlap.
- The remaining p orbitals of each carbon atom then overlap sidewise to form the pi bond.

5. **Conclusion:**
Therefore, a double bond consists of one sigma bond and one pi bond, resulting from the combination of head-to-head and sidewise orbital overlaps.

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