(Steps by steps)
1. A table of the periodic elements is available.
2. Students must decode a series of numbers, for example: 15; 67; 10.
3. Each number represents the atomic number of a chemical element.
In the case of the numbers 15, 67, 10 they are: Phosphorus, Holmium, Neon.
4. After finding the appropriate elements, students should replace the numbers with letters representing the given elements.
In this case, P, Ho, Ne.
5. A password can lead (for example) to another puzzle.
The process can also be reversed, with the students having the elements and needing to find the corresponding atomic numbers to find the code to something.