Mô hình VSEPR tứ diện

Whenever we learn the shapes of molecules using the VSEPR method, the angles between the bonds in a tetrahedral molecule (e.g. methane, silane, sulfate anion, etc.) cannot be reliably estimated at first glance (for a triangle it can be seen that it is 360/3=120°, for a trigonal bipyramids 90° and 120° respectively). Moreover, the value 109° 28' is not a pretty number.
The calculation is not complicated and there are many paths to it; one of them is over volume. The model tries to show that the volume of a tetrahedron is the sum of the volume of 4 trigonal pyramids.
The model can be printed as 4 trigonal pyramids, or as one + tetrahedron without one of them.