As
we all know that the atom is the smallest particle of element. Size of
the atom are very small less then 100 picometers. Atom consist of three sub
atomic particle named as electron (negatively charged) proton (positively
charged) neutron (chargeless). There are different theories to explain the
structure of atom and arrangement of sub atomic particle in atom. At first the
greek philosopher Democritus believed that atoms were indivisible but his ideas
didn't agree with later scientific theory.
Dalton Atomic model
John Dalton was a British School teacher published theory of atom in 1808.This was
the first modern atomic theory his theory of atomic structure was based on the
law of chemical combination
The major postulates of Dalton's atomic
theory
1. Every matter composed of
small particles called atoms.
2. Atoms of the same
element are similar in shape and mass, but differ from the atoms of other
elements.
3. Atoms can nither be
created or nor be destroyed.
4. Atoms of different
element may combine with each other in a fixed,simple, whole number ratios to
form compound atoms.
5. The atom is the smallest
unit of element and can take part in a chemical reaction.
Drawabacks of Dalton
atomic model
1.
This theory didn’t explain about the sub
atomic particle electron, proton and neutron.
2.
This theory fail to explain about the existence
of allotropes.
3.
Fail to explain about the isobars.Fail to explain about
isotopes.
Thomsom
atomic model
According to thomsom
atomic model an atom is a positive sphere in which electorn are embedded like seeds
in watermelon. Hence this theory is also called thomsom watermelon atomic model
This model had no theoretical and practical justification and was soon discard
Drawbacks of Thomsom atomic model
. This theory didn't explain about the positively charged particle in atom.
.This theory didn't explain about the stability of atom
.This theory didn't tell us anything about the nucleus of atom.
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