Question

How did the discovery of isotopes contradict Dalton's atomic theory?

Answer 1

Dalton's atomic Theory

1. ​All matter is made up of tiny, indivisible particles called atoms.
2. All atoms of a specific element are identical in mass, size, and other properties. However, atoms of different elements exhibit different properties and vary in mass and size.
3. Atoms can neither be created nor destroyed. Furthermore, atoms cannot be divided into smaller particles.
4. Atoms of different elements can combine with each other in fixed whole-number ratios in order to form compounds.
5. Atoms can be rearranged, combined, or separated in chemical reactions.

• Dalton had said that all atoms of the same kind have the same mass but atoms of different atoms had different masses.
• The discovery of isotopes showed that all atoms of the same type did not have the same mass.
• Our modern periodic table list the average atomic mass of all the isotopes of a given type of atom.​
• For example Carbon-12, carbon-13, and carbon-14. A carbon atom has 6 protons and 6 neutrons are carbon 12. When one extra neutron is added to this atom then it is known as carbon 13. It is heavier than a C-12 atom. When 2 neutrons are added to a carbon-12 atom, then it is known as a Carbon-14 atom. which means the same particle is named carbon but its isotopes have different masses.

Hence, the discovery of isotopes contradicts Dalton's atomic theory