Electrophilic addition: In this mechanism a positive species approaches the double or triple bond and in the first step forms a bond by converting the π pair of electrons into a σ pair

Step-1

Step-2

In the reaction, X need not actually be a positive ion but can be the positive end of a dipole or an induced dipole, with the negative part breaking off either during the first step or shortly after. 

Not all electrophilic additions follow the simple mechanism. In many cases, if (1) forms, it very rapidly cyclises giving cyclic intermediate (2)

Whether intermediate is (1) or (2), the mechanism is called electrophilic addition bimolecular. Stability of intermediate (1) or the formation of (2) controls the stereochemistry of the reaction. As the stability of (1) increases, rotation along C–C is possible, reaction may be non-stereospecific.