Structure of Atom Class 11 Notes Chemistry Chapter 2
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Institution
Get complete class-11 Chemistry Chapter-2 notes - Structure of Atom. These detailed notes for class-11 Chemistry to prepare for Board's as well as competitive exams like IIT JEE, NEET etc..
Atomic Structure
Atom is made up of smaller units like
proton, neutron and electron. Some
other particles like positron, neutrino,
antineutrino, π-meson, μ-meson, k
meson etc are also present which are
very short lived.
Discovery of Electron
In 1879, William Crooks studied the
conduction of electricity through gases
at low pressure. He performed the
experiment in a discharge tube which
,is a cylindrical hard glass tube about
60 cm in length. It is sealed at both the
ends and fitted with two metal
electrodes. The electrical discharge
through the gases could be observed
only at very low pressures and at very
high voltages.
J.J. Thomson took a discharge tube and
applied a voltage of a 10000 volt
potential difference across it at a
pressure of 10–2 mm of Hg. He found
some glowing behind anode. It means
some invisible rays produced at
cathode strike behind anode and
produce fluorescence. He named them
cathode rays.
Properties of Cathode Rays
,1.These rays have mechanical energy
and travel in straight line.
2.These rays are deflected towards
positive plate of electric field. It means
these are made up of negatively
charged particle called electron.
3.Colour observed is independent from
nature of gas.
4.Mulliken determined the charge on
electron which is 1.602 × 10–19 C.
5.Specific charge on electron is
calculated by J.J. Thomson.
Charge to mass ratio
J.J. Thomson for the first time
experimentally determined
charge/mass ratio called e/m ratio for
the electrons. For this, he subjected the
beam of electrons released in the
discharge tube as cathode rays to
influence the electric and magnetic
fields. These were acting
perpendicular to one another as well
as to the path followed by electrons.
, According to Thomson, the amount of
deviation of the particles from their
path in presence of electrical and
magnetic field depends on
1.Magnitude of the negative charge on
particle
2.Mass of particle
3.Strength of magnetic field
When electric field is applied,
deviation from path takes place. If only
electric field is applied, cathode rays
strike at A. If only magnetic field is
applied, cathode rays strike at C. In
absence of any field, cathode rays
strike at B.
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