Atomic & Mass Number Simulation

Mass Equation

1

Mass (A)

=

1

Protons (Z)

+

0

Neutrons

*Electrons have negligible mass and do not affect A.

Quick Select (Periodic Table):

Protons (p⁺)

Neutrons (n⁰)

Electrons (e⁻)

Net Charge: 0

Sim Speed

An atom has an Atomic Number (Z) of 8 and a Mass Number (A) of 18. How many neutrons does it have?

Atomic Number (Z) = Number of Protons. It uniquely identifies the chemical element.
Mass Number (A) = Protons + Neutrons. These are the heavy particles in the nucleus.
Isotopes are atoms of the same element (same Z) but different mass (different A).
Experiment: Watch the Isotope Notation box. Add a neutron. Does the element symbol change? Add a proton. Now what happens?