The modern structure of the atom, with a dense, positively charged nucleus surrounded by negatively charged electrons, is largely credited to Ernest Rutherford.

Here's a breakdown of his contribution:

* The Gold Foil Experiment: In 1911, Rutherford conducted the famous gold foil experiment. He bombarded a thin sheet of gold foil with alpha particles (positively charged). Most of the particles passed straight through, but some were deflected at large angles, and a few even bounced back.

* Nuclear Model: Rutherford interpreted these results to mean that the atom's positive charge was concentrated in a tiny, dense region he called the nucleus. He proposed that the electrons were scattered around the nucleus in a vast, mostly empty space.

However, it's important to note that Rutherford's model wasn't complete:

* It didn't explain why electrons didn't spiral into the nucleus due to electromagnetic attraction.

* It couldn't explain the different spectral lines observed in the light emitted by atoms.

Later, Niels Bohr developed a more refined model, which incorporated quantum mechanics and explained the stability of the atom and its spectral lines.

So, while Rutherford's model laid the foundation for the modern structure of the atom, it was the work of Bohr and other scientists that further developed and refined our understanding.