Subatomic Particles Practice
Isotope notation encodes the particle counts: the atomic number gives the protons, the mass number minus the atomic number gives the neutrons, and the charge tells how the electrons differ from the protons.
Fill in the missing particle counts for each species below.
Common Questions
How do you find the number of protons in an atom?
The number of protons equals the atomic number (Z), which is unique to each element and found on the periodic table. For example, carbon always has 6 protons.
How do you find the number of neutrons?
Neutrons = mass number (A) minus atomic number (Z). The mass number is the total number of protons and neutrons in the nucleus. It is given as a superscript in isotope notation.
How do you find the number of electrons?
For a neutral atom, electrons equal protons (atomic number). For ions, subtract the charge: cations have fewer electrons (Na+ has 10), anions have more electrons (Cl- has 18).
What is an isotope?
Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons. They have the same chemical properties but different masses. For example, carbon-12 and carbon-14 are isotopes of carbon.