BOOK_CONTENT
From Common Isotopic Elements and their Properties

Properties of Isotopes

The number of electrons present inside an atom or element determines the chemical properties of the atom or element. Because the number of electrons in an atom and its isotopes are the same, the chemical properties of an isotope are similar to that of the parent atom. On the other hand, heavy isotopes have large masses and different chemical properties as compared to their parent atoms. This phenomenon is termed as Kinetic Isotope Effect.

Kinetic Isotope Effect

Kinetic Isotope Effect is defined as a variation in the rate of chemical reaction because of the substitution of atoms by isotopes. This effect occurs when an atom in one of the reactants is replaced by one of its isotopes. Consider the following reaction:

A+D ? E

The effect of isotopic substitution of reactant A is expressed as the ratio of rate constants kl/kh, where the superscripts l and h represent reactions in which the molecules of reactant A contain light and heavy isotopes. Any such substitution modifies the reaction rate significantly. The reaction rate will also change when a chemical bond is broken or formed during complete isotopic replacement. This process of change in reaction rate is called Primary Isotope Effect.

When the substitution of atoms by isotopes does not involve the breakage or formation of bonds, the change in reaction rate is quite small and is termed Secondary Isotope Effect.

The phenomenon of change of rate of a reaction and the magnitude of the Kinetic Isotope Effect...

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