Final answer:
Dalton's theory originally stated that atoms can neither be created nor destroyed in chemical reactions, aligning with the law of conservation of mass. However, advancements in nuclear chemistry have shown that atoms can be transformed, thus effectively created or destroyed, and that atoms of the same element can have different masses due to isotopes.
Step-by-step explanation:
The statement that 'atoms can neither be created nor destroyed in a chemical reaction' is actually a part of Dalton's atomic theory and reflects the law of conservation of mass. Dalton's theory posits that atoms are indestructible during chemical changes and are merely rearranged. This concept is foundational to the understanding of chemical reactions. However, modern science has made revisions to Dalton's theory with the advent of nuclear chemistry.
Through processes like nuclear fission and fusion, we now understand that atoms can actually be transformed into other atoms, effectively creating or destroying them at the nuclear level. Furthermore, while Dalton believed that all atoms of a given element were identical in mass, isotopes have proven that atoms of the same element can differ in mass.