CBSE Class 9 Chemistry Structure of the Atom
Model of An Atom
J.J. Thomson proposed that electrons are embedded in a positive sphere.
The mass of positively charged proton and neutral neutron is one unit each.
The mass of negatively charged electron is about 1/1840 times the mass of a proton.
Discovery of Nucleus
Rutherford's alpha-particle scattering experiment led to the discovery of the atomic nucleus.
The stability of the atom could not be explained by this model.
Niels Bohr's proposed that electrons are distributed in different shells with discrete energy around the nucleus.
Maximum number of electrons that can be accommodated in the outermost shell is 8.
Valency is the combining capacity of an atom.
Parameters of an Atom
An atom is neutral as the number of protons is equal to the number of electrons
Isotopes are atom of same element, with different number of neutrons. Isobars are atom of different elements with same mass number.
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