After the assumptive base comes the observational base of chemistry. This is the layer where observation does its work, where we begin to look at what is in front of us and to describe it. It is the descriptive level of the subject made concrete.
The organizing concept here is the phase. With phase in hand, matter can be classified: mixtures, solutions, compounds, and elements. Each of those is a way the world arranges itself, and each can be described without reaching for any explanation of why. By the way, a phase has nothing to do with solids, liquids, or gases. That is a separate matter, and a common confusion.
This is also the layer that distinguishes the work here from theoretical chemistry. The observational base does not look past what can be observed. It does not ask what materials are made of underneath. It asks how they appear, how they behave, how one differs from another, and it answers using the concept of phase. That is enough work for a long while.
Question
What does the observational base classify, and what does it use to do the classifying?
Reveal Merrill's answer →Hide answer
It classifies matter, sorting it into mixtures, solutions, compounds, and elements. The tool it uses for the sorting is the concept of a phase. By the way, a phase has nothing to do with solids, liquids, or gases.