The atomic number of an element tells us the number of protons in the nucleus of an atom of that element.

So, since potassium has an atomic number of 19, this means that potassium has 19 protons in its nucleus.

Here are some additional points to remember:

* Neutral atoms have an equal number of protons and electrons. So, a neutral potassium atom also has 19 electrons.

* The number of neutrons can vary, leading to different isotopes of an element. The atomic mass of an element takes into account the average mass of all its isotopes.