Order DescriptionExplain, in general terms, the distinction between observational and theoretical concepts. Then exemplify the distinction with a scientific theory of your choice. That is, specify for some scientific theory T which theoretical concepts are introduced by T. Further, specify the concepts which are used to describe the phenomena that T is supposed to explain.
Citation style: preferably some author-year-style, such as Chicago.

Literature:
G. Schurz: Philosophy of Science. A Unified Approach, 2014.

R. Carnap: Philosophical Foundations of Physics, Chapter 23 — 25, 1966.

H. Andreas: Theoretical Terms in Science, Stanford Encyclopedia of Philosophy, http://plato.stanford.edu/entries/theoretical-terms-science/.