what is the decimal at the bottom of an element on the periodic table?

Answer:
The atomic mass
Step-by-step explanation:
The decimal at the bottom of an element represents how much one atom of that element weighs.
Answer:
Atomic mass
Step-by-step explanation:
That number is the atomic mass of the element. It is also the same numerical value as the molar mass, which is the mass of 1 mole of the element.
So, in this case, sodium (Na) has an atomic mass of 22.99 atomic mass units (amu).
Hope this helps!