Question

What are isotopes and how does the existence of isotopes contradict daltons theory

Answer 1

Isotopes are the different forms of an element which has same number of electron and proton but different number of neutron hence it differs in mass. For example hydrogen, it has 3 isotopes. It contradicts the Dalton's theory as the theory stated that , all atoms of a given element are identical in mass and properties. Though different forms of atoms of an element are identical in properties but are not necessarily identical by their masses.

I hope you have understood what I explained and are clear with your doubt.  

Answer 2

Explanation:

Isotopes are atoms of the same element with the same atomic number but a different mass number due to the difference in the number of neutrons in their nucleus.

Dalton's theory states that 'Every atom of an element is identical in all respects.' However isotopes are atoms which are different in their mass number. In this way the existence of isotopes contradict Dalton's theory.