# In halogenation of ethene using bromine for example, why does the lone pair of bromine attack the C atom?

In the presence of the electron rich (pi bond) of ethene, the bromine molecule becomes a temporary induced dipole, one end being electron deficient and acting as the electrophile. (The pi bond in) ethene attacks the electrophile.

At the same time, one of the lone pair of electrons in bromine attacks one of the C atom. Why does this happen?

Normally, I'm familiar with the same process, but with the carbocation being formed without the lone pair of electrons of bromine attacking the other C atom:

Does this have something to do with resonance as shown by the diagram below?

• The alkene's filled π orbital is higher in energy than the empty σ* orbital of the $\ce{X-X}$ bond. Also, the $\ce{X-}$ can attack the halonium ion but the result is just regeneration of halogen and the alkene: the first step of the reaction is reversible. – Apoorv Potnis Feb 11 '18 at 7:28