NUCLEUS AND ITS COMPOSITION

NUCLEUS AND ITS COMPOSITION

Nucleus and Nuclear Particles:
Nucleus is small and positively charged part of an atom at the center where entire mass of the atom is concentrated. E. Rutherford and his co-workers conducted a series of scattering experiments, on the basis of which the existence of the nucleus was first proposed in1911. These experiments helped to understand the arrangement of sub atomic particles (electrons, protons and neutrons) in an atom. From the experimental observations it was concluded that the protons and neutrons are present in the nucleus where as electrons are present in the empty space around the nucleus.
ATOMIC NUMBER: It is the numbers of electrons present outside the nucleus or the number of protons present inside the nucleus. It is denoted by (Z).
Atomic Number (Z) = Number of electrons (e) OR Number of Protons (p)

NUCLEONS: The sub atomic particles (protons and neutrons) of nucleus are collectively called nucleons. The total number of nucleons is denoted byA and is called mass number of the nucleus.
Mass Number (A) = Number of Protons (p) + Number of Neutrons (n)

REPRESENTATION OF NUCLIDE: The nucleus of any atom is represented by specifying the atomic number as a subscript at the left hand bottom of the atomic symbol and mass number as a superscript at the left hand top of the symbol. For example, carbon atom, its symbol is C; atomic number is 6, mass number is12. It is represented as12c .Such symbols are called as nuclides.

NUCLEAR DIMENSIONS:

The radius of the nucleus is of the order of 10-12 and that of atom is 10-8
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The radii of the various nuclei can be calculated by the following relation
r= R0A1/3
Where; r= radius of nucleus
A= mass number
R0 = constant (1.4 x 10-24cm)
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Nuclear Dimensions are expressed in Fermi units, 1Fermi = 10-13cm.

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Area of cross section of nucleus is measured in unit called barn
(1barn = 10-24cm2)
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Radius of nucleus is 105 times smaller than that of atom.
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Density is of the order of 1014gcm-3.
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Volume is of the order of 10-38 cm3.



ISOTOPES, ISOBARS, ISOTONES,
Isotopes:
These are the atoms having same atomic number but different mass numbers.
They contain same number of protons but different number of nucleons.
Isobars:
The atoms having different atomic numbers but same mass number are called isobars. They contain same number of nucleons but different number of protons.
Calcium and Argon are isobars of each other having same mass number but different atomic number.
Similarly Lead and Bismuth are isobars of each other.
Isotones:
These are the atoms having same number of neutrons but different number of nucleons. But by appearance they have different number atomic number and different mass number but the number of neutrons is same all these nuclides have different mass number and atomic number. But if we calculate the number of neutron in each case it is coming out to bethe16.
Because Number of neutrons = mass number (A) – atomic number (Z)