Download Structure of atom

Structure of atom
STD 9
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Concepts
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Charged particles of matter
Thomson’s atomic model
Rutherford’s model
Bohr’s model
Sub-atomic particles
Electron orbits and valency
Atomic number and mass number
Isotopes and isobars
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Charged particles of matter
• Electron – negatively charged subatomic
particle
• Proton – positively charged subatomic particle
• Ion – charged particle – e.g. H+, Cl• Cation – positively charged ion , e.g. Ca2+
• Anion – negatively charged ion , e.g. Br-
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J J Thomson determined the value of e/m (specific charge of electron)
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J. J Thomson’s Cathode Ray Experiment
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Alpha particles
• Doubly charged Helium ions
• Mass 4 u
• Fast moving alpha particles have great amount
of energy.
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Rutherford model
• Nucleus – positively charged centre of the
atom
• All mass of atom resides at the centre
• Electrons revolve around the nucleus in
circular orbits
• Size of the nucleus is smaller than the size of
the atom
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Drawbacks of Rutherford’s model
• The revolution of electron in the circular orbit is
not stable.
• It would undergo acceleration.
• During acceleration charged species will radiate
energy.
• The electron will lose its energy and finally fall
into the nucleus.
• Hence atom becomes unstable.
• This is not acceptable since atom is neutral and
stable.
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Failure model of Rutherford
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