Chemistry question?

Question

Fluorine has a single atomic species, 19F. Determine the atomic mass of 19F by summing the masses of its protons neutrons and electrons, and compare with the value of the atomic mass from the periodic table. Explain why the agreement is poor

Answer 1

You're a big boy, I'll let you do the arithmetic. Hint -- the difference is about 0.1598 amu

The difference represents the binding energy of the nucleus.