A double bond has two distinct and different parts. The first part is called a sigma bond. This forms when electron clouds overlap head-on between the atoms.
The second part is called a pi bond. This forms when p orbitals overlap sideways above and below the atoms. You can think of p orbitals as dumbbell-shaped clouds of electrons.
The pi bond locks the atoms into a flat shape. Breaking this sideways connection takes a large amount of energy. Because of this, atoms cannot spin freely around a double bond.
This fixed shape creates different chemical structures called isomers. Students often think a double bond equals two identical single bonds. This idea is a very common student misconception.
The sigma and pi bonds have completely different shapes and strengths. The sigma bond is actually much stronger than the pi bond. A double bond is shorter and stronger than a single bond.
It pulls the two bonded atoms closer together. But it is weaker than a carbon triple bond. The exposed electrons in the pi bond make the molecule reactive.
Other chemicals can attack these outside electrons to form new bonds. This chemical process is known as an addition reaction. Plant oils have many carbon double bonds in their long chains. These rigid bonds keep the oils liquid at room temperature.