You're asking about the location in the periodic table where you'd find the least massive atom. Here's how to break down the answer:

* Atomic Mass: The mass of an atom is primarily determined by the number of protons and neutrons in its nucleus.

* Periodic Trends: As you move across a period (from left to right) in the periodic table, the atomic number increases, meaning more protons are added. As you move down a group (from top to bottom), new electron shells are added, increasing the atomic size.

Therefore, the least massive atom would be located in the top left corner of the periodic table. This is where you find hydrogen (H), the lightest element.

Let me know if you have more questions!