Use curved arrows to show the movement of electrons in each equation.

a.

b.

Carbon atoms having a positive charge (lack of an electron) are called carbocations and the ones having excess electrons that are indicated using a negative charge over the carbon atom are called carbanions.

Neutral carbon atoms that have an unpaired electron over them are termed carbon radicals.

a.

Movement of electrons in reaction a

Both the species consist of carbon radicals.

Each donates one electron each, resulting in a bond.

b.

Movement of electrons in reaction b

Electrons move from negatively charged species (species-rich in electrons) to positively charged species (electron-deficient).

Here, the bromine atom is electron-rich and it donates both the electrons to the carbocation resulting in a bond.