The Periodic Law states that when elements on the periodic table are organized by increasing atomic number, patterns start to emerge.
Items in the same group (vertical columns) all share an identity trait. In this case, everything in Group 1 is a television, everything in Group two a cell phone, etc.
A you move across a period (horizontally from left to right), there is a change in a characteristic. The periodic part about this concept is that when you get to the next period, the same change is observed. In this case, the periodicity is seen with the price of the devices within a each period. In each period, the devices start at the lowest price and you move across the period the price increases.
Students can choose their PT topic from a provided list, or they can use their own topic. Some of the topics used include: dog breeds, cheese, shoes, cuisine, board games, etc.