.What are the failures of Dalton's Atomic theory?
(i) It does not account for subatomic particles: It stated that atoms were the smallest unit of matter. But, the discovery of subatomic particles namely, protons, electrons, and neutrons disproved this postulate. (ii) It does not account for isotopes: For example hydrogen 1 H1 , deuterium 2 H1 , and tritium 3 H1 , have the same atomic number, but different mass numbers. (iii) It does not account for isobars. Example: 40 Ar18 and 40 Ca 20 , they have different atomic numbers, but the same mass number. (iv) Elements need not combine in simple, whole-number ratios to form compounds: There are complex organic compounds that do not combine in simple ratios of constituent atoms. Example: sugar/sucrose ( C H O 11 22 11 ). (v) It does not account for allotropes: The differences in the properties of diamond and graphite, even though they contain only carbon, cannot be explained by Dalton’s atomic theory.
