Explain the structure of an atom, including its subatomic particles, their locations, and the concept of mass number. Illustrate with an example if possible.

1 (a)
Dalton's theory was proven inaccurate because atoms are not indivisible. They are composed of smaller subatomic particles: protons, neutrons, and electrons.

1 (b)
The two regions of an atom where smaller particles are located are the nucleus (containing protons and neutrons) and the electron shells/orbitals (containing electrons).

2 (a)
Protons and neutrons are collectively called nucleons because they are both located within the nucleus of an atom. The term "nucleon" specifically refers to particles found in the atomic nucleus.

2 (b)
The particle that orbits this central region (the nucleus) is the electron.

3 (a)