In the interactive, start adding neutrons to the nucleus.Describe what happens to the mass number each time you add a neutron, and why.

Understanding Neutron Addition to the Nucleus

1. Definition of Mass Number: The mass number of an atom is the total number of protons and neutrons in its nucleus. It is represented by the symbol $A$.

2. Addition of Neutrons: Each time a neutron is added to the nucleus:

   • The number of neutrons increases by one.
   • The number of protons remains unchanged.

3. Effect on Mass Number: Since the mass number $A$ is calculated using the formula: $A = Z + N$ where $Z$ is the number of protons and $N$ is the number of neutrons, adding a neutron results in: $A' = A + 1$ The new mass number $A'$ now reflects the additional neutron.

4. Reasoning: Neutrons contribute to the overall mass of the nucleus as they have a relative mass approximately equal to that of protons but no electric charge. Thus, adding neutrons increases the mass of the atom without affecting its chemical identity, which is determined solely by the number of protons.

Summary of Changes to Mass Number

Each time you add a neutron to the nucleus, the mass number increases by one. This increase reflects the additional mass contributed by the neutron while the atomic properties (like the element's identity) remain unchanged.