ATOMIC STRUCTURE: -
Fundamental
particles-
Atom consists of three
fundamental particles namely: electron, proton and neutron.
proton was discovered in
1886, electron in 1897 and neutron in 1932. in addition to these
three fundamental
particles, other particles have also been discovered. in 1932 Yukawa
predicted the existence
of a new kind of particle meson which keeps protons and neutrons
together in the nucleus.
Electron was discovered by Sir J.J. Thomson. It is negatively charged
particles having
relative charge _1 unit and has relative mass 1/1840 (approx. Zero).
Goldstein found another
particle which was positively charged called proton. Proton has
relative charged of +1
unit and also has relative mass of 1 unit. The charged of proton (e+) is
numerically equal to
that of electron (e-) with reverse sign. The proton is indicated as p (+1p1).
James Chadwick
discovered the new fundamental particles neutron by bombarding Be with fast
Moving αΎ³-particles.
4Be9 + 2 He4 → 6C12
+ 0n1
Because of neutron character
it is neutron. Neutron is neutral (charge=0)
and relative mass of
1unit. The neutron is indicated as 0n
With the discovery of
these fundamental particles question arose with respect
To the arrangement of
these particles inside an atom. Early models of the atom
Was propose by J.J.
Thomson, Rutherford and Bohr.
protons and neutrons are
in the nucleus of the atom and electron move around the nucleus in orbits of
fixed energy. Nucleus is at the Centre of the spherical atom and its radius is 10-13 cm and radius of an atom is 10-8
Cm. Nucleus is 1 lac time smaller than an atom. The charged of the nucleus is positive and is equal to the number
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of
protons present in it. The mass of the nucleus is the sum of the masses of
protons and neutrons present in it. Hence, the atom can be shown an indicated
in figure 1.
Radius of nucleus ≈ 10-13 cm.
Radius of nucleus ≈ 10-8 cm.
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