Here's why:

* Atomic Radius: The atomic radius is a measure of the size of an atom. Sodium (Na) is in Group 1 (alkali metals) and silicon (Si) is in Group 14 (carbon group) of the periodic table.

* Periodic Trends: As you move across a period (from left to right) in the periodic table, the atomic radius generally decreases. This is because the number of protons in the nucleus increases, pulling the electrons closer to the nucleus.

* Electronegativity: Sodium has a lower electronegativity than silicon, meaning it holds its electrons less tightly. This further contributes to sodium having a larger atomic radius.

Therefore, a silicon atom is larger than a sodium atom.