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

Explanation

To understand how the discovery of isotopes contradicted Dalton's atomic theory, we need to break down the key components of Dalton's theory and the implications of isotopes.

### Step 1: Review Dalton's Atomic Theory
Dalton's atomic theory, proposed in the early 19th century, included several key postulates:
1. All matter is made up of indivisible atoms.
2. Atoms of a given element are identical in mass and properties.
3. Atoms of different elements differ in mass and properties.
4. Compounds are formed by the combination of atoms of different elements in fixed ratios.
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