Atetrahedron is like a pyramid, but with a triangular base. how might atoms bond to form this shape?

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.

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explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

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since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.