# What element in the second period has the largest atomic radius?

We look at $L i$, $Z = 3$, versus $N e$, $Z = 10$.
As scientists we should always consider the data . The atomic radius of $L i$ $=$ $167 \times {10}^{-} 12 m$; the atomic radius of $N e$ $=$ $38 \times {10}^{-} 12 m$.
This is quite a stunning decrease in radius. Atomic radii decrease ACROSS the Period going from left to right due to increased NUCLEAR CHARGE. As $Z$ increases sequentially, the effective nuclear charge increases as the electrons, adding to the same shell, shield each other VERY imperfectly, and atomic radii contract.