Question

A _________________ is developed through the scientific method, and it can be modified or improved upon. It may be represented by a model. As seen here, three different models were used to represent atomic structure as ideas changed over time.

Answer 1

I think that the best phrase to fit into the blank is a "scientific theory".

A scientific theory is developed through experiments which use the scientific method, and a theory can be improved if additional data is available or if people provide suggestions which make the theory fit the data better. 

Answer 2

A simple answer to this "a theory".