There are three halogenoalkanes with halogens F, Br and I. Each undergo an SN2 reaction. How does the rate of reaction differ between the three halogenoalkanes?

The Iodoalkane will have the fastest rate of reaction. The Bromoalkane will have the second fastest, while the Floroalkane will have the slowest. This is because the atomic radius increases from Florine to Iodine and electronegativity decreases from Florine to Iodine. Essentially Iodine has a lot more electrons around its nucleus than Bromine and Florine. This means it has a weaker pull on electrons (weaker Z_eff). Therefore, C-I bonds are going to be weaker and easier to break than C-Br and C-F bonds so the rate of reaction will be faster.