Correction: The lattice spacing gives the size of the fundamental building block of the lattice, which includes several atoms. The nearest neighbour distance in the lattice is 0.235 nm.

Wikipedia has a nice picture of the lattice structure:

https://en.wikipedia.org/wiki/Diamond_cubic#/media/File:Visu...

Part 3 of the picture is a 3x3x3 block of elementary cells, for silicon this would be 1.63nm along each edge, so for a 2nm element you get a few more atoms in each direction.