Use candy! Like gumballs, twizzlers, m&ms, whatever works for you. Hold the pieces together with gum too.

Just make Helium and have 6 balloons filled with helium. Make the protons red balloons, electrons blue balloons and neutrons white balloons.

Get a round, as nearly spherical, clear glass/plastic goldfish bowl that you can find.

Get some 2 lb test fishing line, and a small split shot BB lead from a fishing store. Get two different colors of paint.

Clamp the split shot to one end of the fishing line. Paint dots at least 12 dots on the surface of the split shot; be sure to paint an equal number of each color of dot.

Use the fishing line to suspend the BB in approximately the middle of the bowl.

Fill the bowl with shaving cream or whipped cream.
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The split shot lead represents the nucleus of the atom.

It represents the entire nucleus of more than 16 protons and neutrons. [If the instructor doesn't believe you, then be prepared to extract the lead shot from the atom, and use a very sharp knife to cut it into pieces -- argue that each piece represents a proton or neutron, and that it is hard to cut apart because you have to overcome the model's nuclear strong force to do it.]

The whipped cream represents the electron cloud surrounding the nucleus. Like the real electron cloud, it represents most of the volume of the atom. Also like the real electron cloud, if you stick your hand in to try to grab an individual electron, the cloud configuration changes in response to your observation/sampling. Because of the quantum mechanical nature of what you’re modeling, it doesn’t make sense represent the electrons as particles. The Heisenberg Uncertainty principle says you can’t know both the position and momentum exactly, and you don’t know the quantum energy state of this particular atom, so you compromised and represented the electron cloud surrounding the nucleus as a malleable cloud of shaving cream, contained in the vicinity of the nucleus by the fish bowl. Orbital and sub-orbital shells were not EXPLICITLY modeled, again, because the quantum energy state of this particular atom is unspecified/unknown.

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Extra credit:
Bring in two fishbowl atom models and some masking tape. Demonstrate/argue that you can model atom-atom bonding by placing the mouths of the two fishbowls together, then using the masking tape to tape them together.

Further argue that you’re the model for the catalyst that facilitates the atom-atom bonding.