Isotopic effects
Definition of isotopes
Isotopes may be
defined as :
(1) The atoms of an element which have the same
number of protons and different number of neutrons are called Isotopes.
(2) The atoms of an element which have the
same atomic number but different atomic masses or mass numbers.
Examples of isotopes
Isotopes of Hydrogen
Isotopes of Neon
Isotopes of Oxygen
Isotopes of Chlorine
** Although in
many respects the chemistry of the isotopes of an element is the same, there
are significant differences between them due to difference in masses.
** Thus the
physical properties of the compounds of each isotope of an element are
distinctly different from those of others.
** Similarly,
reaction rates of the individual isotopes are also different.
** The
differences in isotopes due to mass differences are termed Isotopic Effects.
** The isotopic
effects show up clearly in the isotopes of hydrogen 1H1and 2H1 (D)
.
** The
differences in the physical properties of water from ordinary hydrogen 1H1 and
heavy hydrogen D are listed in this Table
** The isotopic
effects are also exhibited by the difference in the reaction rates of the two
isotopes of hydrogen.
** Under similar
conditions, the reaction of the heavy isotopes with chlorine is about six times
slower than that of light isotope.
** This
difference in reaction rates is explained by the fact that the covalent bond
formed by deuterium is slightly stronger than the corresponding bond with
ordinary hydrogen. Hence a reaction that breaks a deuterium covalent bond is
slower than the same reaction involving bond to light hydrogen.
Applications of isotopic effects
** There are
several useful applications of isotopic effects.
** One method of
separation of isotopes of hydrogen depends on the fact that the electrolysis of
heavy water (D2O) is slower than the electrolysis of normal water.
** Pure heavy
water is a valuable by-product of the electrolysis of water, since large
quantities are required in nuclear reactors to moderate the rate of the uranium
fission reaction.
Reference: Essentials of Physical Chemistry /Arun
Bahl, B.S Bahl and G.D. Tuli / multicolour edition.
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