What are isotopes?
What are Isotopes?
** Contrary to
Dalton’s Atomic theory, all atoms of a given element are not necessarily
identical. In fact, most elements have been shown to be composed of two or more
types of atoms mixed in a fixed proportion.
** The different
atoms of such an element contain equal number of protons and, therefore, have
the same atomic number.
** The atoms
which vary from one another have different number of neutrons in the nucleus.
Thus they have different atomic masses.
** 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.
** The name
‘isotope’ was assigned to them by Soddy because they have the same atomic
number and hence occupied the same place in the periodic table (Greek, isos =
same; topos = place).
** Isotopes have
similar chemical properties as they have the same electronic
configuration. However, they differ in respect of physical properties which
depend on atomic mass.
Symbolic representation of isotopes
** In denoting
particular isotopes of an element, the following notation has been
internationally adopted.
** The symbol of
the element is written with atomic mass at the head and atomic number at the
bottom.
** Alternatively,
the name of the element is followed by the atomic mass with a hyphen (-) in
between.
** EX: Thus the isotopes of carbon (atomic number 6)
having atomic masses 12 and 14 may be written as:
Examples of isotopes
** Since
isotopes of an element have the same atomic number, each of these contains
equal number of protons. They have different atomic masses which is accounted
for by the different number of neutrons present in the nucleus. Thus the
isotopes of an element are characterised by different number of neutrons in the
nucleus.
** The atomic
structure of an isotope with atomic number Z and mass number A (atomic mass in
amu) can be given as follows :
(1) The number
of extranuclear electrons = Z
(2) The number
of protons in the nucleus = Z
(3) The mass
number A is equal to the total number of protons (Z) and neutrons (N) in the
nucleus. That
is,
A = Z + N
∴ N = A – Z
Isotopes of
Hydrogen
Isotopes of Neon
Isotopes of
Oxygen
Isotopes of
Chlorine
Isotopes of
Uranium
Reference: Essentials of Physical Chemistry /Arun
Bahl, B.S Bahl and G.D. Tuli / multicolour edition.
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