Which statement is NOT part of Dalton's Atomic Theory?

• A. Atoms only change when mixed with other elements
• B. Elements are composed of atoms
• C. Atoms of the same element are identical, but differ from other elements
• D. Elements can mix together

Answer: (D)

Dalton's Atomic Theory explains how atoms combine and rearrange to form substances. It says that elements are made of atoms, atoms of the same element are identical (and different from atoms of other elements), and compounds form when atoms combine in simple whole-number ratios; chemical reactions involve rearranging atoms, not changing their identities.

The statement about elements simply mixing together describes a physical blending in a mixture, not how atoms join to form compounds in definite ratios. That is why it doesn’t fit Dalton’s theory. The other ideas—elements made of atoms, identical atoms within an element, and atoms rearranging to form compounds—are all consistent with his view.