No person has ever looked inside an atom: How do we know that atoms are made of?

Numerous scientists have made significant contributions to our understanding of atomic structure. In certain cases, these discoveries have resulted from outstanding experiments that have demonstrated what must be inside an atom; examples of these experiments include the work of J. J. Thomson and Ernest Rutherford, who discovered the electron and the nucleus, respectively.

In other instances, such as the hydrogen line spectrum in the case of Bohr's work leading to the first quantum atom, progress has been made as a result of attempting to get the atom to "behave" in accordance with previously known experimental results.

In any case, the discoveries were of the kind that led one to conclude, "This atom must be like this. If this isn't true, then there isn't a straightforward way to explain what we have just discovered."

This does not imply that we can know with certainty that the atom is that way; rather, it illustrates how science operates by offering precise explanations for natural facts, even when those explanations go against "common sense".

Together with theoretical models, experimental data from methods like X-ray crystallography, electron microscopy, and spectroscopy reveal the structure of atoms and their constituent subatomic particles, such as protons, neutrons, and electrons.