The atomic number of an element determines the number of protons and electrons in an atom. For potassium (K), the atomic number is 19, which means it has 19 protons and 19 electrons.
The atomic mass of potassium-39 refers to the total number of protons and neutrons in the nucleus. To find the number of neutrons, subtract the atomic number (protons) from the atomic mass.
Atomic number (Z) = 19 (number of protons) Atomic mass (A) = 39
Number of neutrons (N) = Atomic mass (A) - Atomic number (Z) N = 39 - 19 = 20
Therefore, in an atom of potassium-39:
- Protons: 19
- Neutrons: 20
- Electrons: 19