Question

according to the document, what might have modeled atoms in the 1800s? invisible balls visible particles complex structures detailed diagrams

Explanation:

In the 1800s, atoms were often thought of as indivisible units, similar to invisible balls (the Dalton - atomic model). At that time, the internal structure of atoms was not well - understood, so they were not modeled as visible particles, complex structures, or detailed diagrams.

Answer:

Invisible balls