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ICSE Class 9 Chemistry Question 17 of 22

Atomic Structure — Question 15

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Question 1(1992)

According to the Dalton's Atomic Theory, atoms of the same element are identical in all respects. But according to the Modern Atomic Theory, this postulate is proved wrong. Explain.

Answer

According to modern atomic theory atoms of the same element may not be alike in all respect as seen in case of isotopes which are atoms of the same element having same atomic number but different mass numbers.

e.g. isotopes of chlorine 1735Cl^{35}_{17}\text{Cl} and 1737Cl^{37}_{17}\text{Cl} have different atomic masses 35 and 37. This proves Dalton's Atomic Theory wrong.