Page 1 - 3. LESSON NOTES-(DALTON'S ATOMIC THEORY AND ITS DRAWBACKS)
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SAI International School
                                                Subject-Chemistry

                                            Ch-Atoms and Molecules
                             Topic-Dalton's atomic theory and its drawbacks
                                                  LESSON NOTE



               Atoms: These are the smallest particle of matter which may or may not have an
                    independent existence and take part in chemical reactions.


               Molecules:  These  are  the  smallest  particle  of  matter  which  can  exist
                    independently.

               Dalton’s Atomic Theory


               1.  The matter is made up of indivisible particles known as atoms.
               2.  The properties of all the atoms of a given element are the same, including mass.
                    This can also be stated as all the atoms of an element have identical mass and
                    chemical  properties;  atoms  of  different  elements  have  different  masses  and
                    chemical properties.
               3.  Atoms of different elements combine in fixed ratios to form compounds.
               4.  Atoms  are  neither  created  nor  destroyed.  The  formation  of  new  products
                    (compounds) results from the rearrangement of existing atoms (reactants) in a
                    chemical reaction.
               5.   The relative number and kinds of atoms are constant in a given compound.

               Merits of Dalton's Atomic Theory


                   The  atomic  theory  explains  the  laws  of  chemical  combination  (the  Law  of
                    Constant Composition and the Law of Multiple Proportions).
                   Dalton  was  the  first  person  to  recognize  a  workable  distinction  between  the
                    fundamental particle of an element (atom) and that of a compound (molecule).


               Drawbacks of Dalton’s atomic theory:


                   The  indivisibility  of  an  atom  was  proved  wrong:  an  atom  can  be  further
                    subdivided  into  protons,  neutrons  and  electrons.  However,  an  atom  is  the
                    smallest particle that takes part in chemical reactions.
                   According  to  Dalton,  the  atoms  of  same  element  are  similar  in  all  respects.
                    However,  atoms  of  some  elements  vary  in  their  masses  and  densities.  These
                    atoms of different masses are called isotopes.
                 Dalton also claimed that atoms of different elements are different in all respects.
                    This has  been  proven  wrong  in  certain  cases:  argon  and  calcium  atoms  each
                    have an atomic mass of 40 amu. These atoms are known as isobars.









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