In this activity, students investigate a puzzle. They are given a set of cards with various properties. Each card has anywhere from 2 to 6 different properties depending on the level of the students and each set of cards has one or two cards missing. The object of the puzzle is to organize and group cards to look for a pattern in order to be able to predict the properties of the missing piece(s). Once the puzzles are completed the students learn about the process Mendeleev and other forerunners used in developing the first periodic tables.