atomic mass 28.0855 g/mol [Wikipedia]
density 2.3290 g/cm^3 [Wikipedia]
==> 2.329000E6 g/m^3
==> 82.925E3 mol/m^3
==> 49.938E27 atoms per metre cubed
==> 20.025E-30 m^3 per atom
If the atom was a cube, each side would be 271E-12 metres.
If the atom was a sphere, its diameter would be 336.92E-12 metres.
If the atom was a tetrahedron, each side would be 553.87E-12 metres.