Yes, sodium ion has a smaller radius than the atom.
Explnation: sodium ion, Na (1+), is a positive ion, which means that the atom has lost one electron. When the atoms lose electrons, they always become smaller. There are two reasons for this: 1) the electron lost is released from the outer shell (valence shell) and this last shell will become empty, which reduces the radius of the atom; and 2) the repulsion force decreases (because there are less electrons), which makes stronger the atraction from the nucleus.
