Tetrahedron generally known as triangular pyramid consists of 4 triangular faces, 6 edges and 4 vertices. The base of the tetrahedron is a triangle. All the vertices have the same atom that is bonded to the central metal atom which lies in the centre of the tetrahedron. We take as an example to see how the atoms actually bond in tetrahedron. It is quite visible from the image that 4 O-atoms lies on all the 4 vertices and 1 Si-atom lie in the centre.
