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The alkene π bond acts as a nucleophile and takes a proton from HX, producing a carbocation and a halide ion. The halide then attacks the carbocation to form the product. For an unsymmetrical alkene, Markovnikov’s Rule predicts that hydrogen adds to the carbon bearing more hydrogens, while the halide attaches to the more substituted carbon; this orientation is associated with formation of the more stable carbocation. The reaction proceeds through a planar carbocation, so attack can occur from either face, and rearrangements may change the product skeleton. The lesson also distinguishes this ionic pathway from anti-Markovnikov addition with HBr and peroxides, which proceeds by a radical mechanism. These ideas help explain regioselectivity, stereochemical outcomes, and important limits of HX addition.