We can take the electrophilic addition of bromine to ethene as an example. The double bond in ethene acts as an area of high electron density causing an induced dipole on the Br2 molecule, giving one of the Br a temporary charge of δ+. One would draw a curly arrow coming from the double bond pointing to the Br with the positive charge and then draw a second curly arrow From the the bond between the two Br’s to the δ- Br. This will then form a [C2H4Br]+ carbo cation and Br- ion. This negative charge attacks the remaining positive charged carbon on the molecule, represented by a curly arrow starting from the negative charge on the bromide and pointing at the positive carbon atom.