If you have a school project to make a 3D model of the sodium atom, you can use several materials. You simply have to purchase the supplies and put it together. A basic knowledge of the periodic table and a lot of glue can go a long way to helping you build a 3D model of Sodium.
Construct the nucleus. A sodium atom has 11 protons and 12 neutrons, so you will need 11 large crafting cotton balls in one color for the protons and 12 in another color for the neutrons. Arrange them into a nucleus by gluing them together in a ball, alternating between protons and neutrons as you glue.
Build concentric circles around the nucleus. Cut three rings out of cardstock or poster board, in three different sizes (going up in size so you have a small, medium, and large ring when finished). Use string to tie these rings in a concentric circle around the nucleus; start by tying the string around the nucleus, then around one edge of each circle so they hang together.
Glue electrons onto the rings. You should have 11 electrons total, which you will make out of the small crafting cotton balls in a color that is different from your protons and neutrons. Glue two electrons to the inner circle of cardstock, eight to the middle circle, and one to the outer circle.
Attach string to the outer circle for hanging, and display your 3D model of sodium.