John Dalton envisioned the atom as a solid, indivisible sphere. He imagined them as tiny, hard balls, like billiard balls, with no internal structure. This model, known as the Dalton model, was a significant step forward in understanding matter, as it proposed:

* Atoms of the same element are identical: All atoms of a given element have the same size, mass, and properties.

* Atoms of different elements are different: Atoms of different elements have different sizes, masses, and properties.

* Atoms cannot be created or destroyed: Atoms are indestructible and can only be rearranged in chemical reactions.

While this model was a breakthrough at the time, it was later found to be incomplete. The discovery of subatomic particles like electrons, protons, and neutrons revealed a more complex structure within the atom.

Here's a simplified analogy: Imagine building a Lego structure. Dalton's model was like assuming each Lego brick was a single, indivisible unit. Later discoveries revealed that each brick itself was composed of smaller, more complex parts.