Final answer:
Dalton's atomic theory differs from modern atomic theory in stating that atoms are indivisible and that atoms of different elements are entirely distinct in their properties. Modern theory shows atoms consist of subatomic particles and isotopes can exist, challenging these claims.
Step-by-step explanation:
One feature of Dalton's atomic theory that differs from modern atomic theory is his claim that atoms of a specific element are indivisible and that atoms of different elements are different in all respects. According to Dalton, atoms were the smallest particles of matter, and they could not be divided into smaller parts. However, modern atomic theory has proven that atoms are composed of even smaller particles known as subatomic particles, including electrons, protons, and neutrons. Additionally, Dalton believed that all atoms of a certain element were identical in mass and properties, but it has been discovered that isotopes exist, which are atoms of the same element with different numbers of neutrons and, consequently, different masses.
Moreover, Dalton's statement that atoms of different elements are different in all respects has exceptions, such as the case of argon and calcium which both have atoms with an atomic mass of 40 amu. This refutes the claim that atoms of different elements are uniquely different, as there can be instances of different elements having the same atomic mass.