Explain why some elements were placed in inappropriate groups in early periodic tables when atomic weight order was followed strictly.

Some elements were placed in inappropriate groups because their chemical properties did not match those of other elements in the same group. This occurred because the arrangement by atomic weight did not account for the atomic number and the actual electron configuration of the elements.

This answer demonstrates an understanding of the limitations of early periodic tables and the importance of atomic number over atomic weight. The question tests the student's ability to connect historical scientific practices with modern understanding of element classification.