Complete the sentence.
Much work was needed to determine the distances between the atoms, the angles between the chemical bonds, and other _______ features.

“Structural” means physical. If one were to insert this term into the text, the sentence would read, “Much work was needed to determine the distances between the atoms, the angles between the chemical bonds, and other structural features.” The missing term must be related to the distances and angles mentioned in the sentence. These features are “structural,” or physical, characteristics.