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 [Kinds of Nuclei]
There occur 94 kinds
of chemical elements
naturally.
The number of kinds of occurring
elements is about one handred
including artifitially produced ones.
Then, is the number of kinds of
nuclei equal to the number of kinds
of elements?
No, they are not equal, because
there are several isotopes
for one kind of element.
An element is specified by
its atomic number
(= the charge of the nucleus).
Accordingly, an element is
sometimes a mixture of
some isotopes with different masses;
their nuclei contain different
number of neutrons.
Each isotope (or nucleus)
is called nuclide.
The number of nuclides
whose existences
have currently been confirmed
is about 3000,
each of which is specified
by its proton number Z
(= the atomic number)
and the neutron number N.
Since the mass of a nuclide is
almost proportional to the number
A = Z + N,
we call
A
the mass number.
To identify each nuclide,
the following symbol
is sometimes used:
where
represents the chemical symbol
(= the symbol of element).
For example,
the nucleus of hydrogen atom;
i.e. proton,
is represented by
 ,
the nucleus of helium atom;
i.e. alpha particle,
is by
 ,
the nucleus of the most popular
nitrogen is
 ,
and the most popular lead is
shown by
 .
The chemical symbols
are listed in the following table:
2-1-A:
Table of Chemical Symbols
Each nuclide can be identified
only by the chemical symbol and
the mass number A.
For a given chemical symbol,
we can know the proton number Z
referring to the
Table of Chemical Symbols,
and then the neutron number
N = A - Z.
Therefore, people sometimes
use the following abbreviated form
For example, lead 208
is represented as
 .
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