We are shown that the atomic number is the number of protons in an atom. We see that the mass number minus the atomic number is the number of neutrons. We complete the atomic structure by explaining that atoms have the same number of protons and electrons. A follow up to this example is given in the second part of the clip.
This clip could be used to show how mass and atomic numbers can explain the numbers of protons, neutrons and electrons in atoms. Following the clip, students could use different coloured balls, (representing protons, neutrons and electrons) and different examples from the Periodic Table to demonstrate what they have learned.