Sizes of ions vs elements

[Astha Patel 2J]

How is it that Na+ is smaller than Cl-, but elemental Na is larger than elemental Cl?

[Andrew Jubintoro 3J]

Na and Cl is in the same period with Na to the left of Cl. This makes Na bigger than Cl.
But when Na becomes Na⁺, it loses its outermost electron that is in the 3s¹ state. This means that the outermost occupied shell of Na⁺ is now the n=2 shell making its radius significantly smaller.

[Inderpal Singh 2L]

Na is to the left side of Cl on the periodic table. By making Na into Na+, you are losing an electron. Since the outermost electron was in the 3 state, by taking it away, the radius drops down to the 2 state/shell. Na was normally larger than Cl but by making it into an ion, it got smaller.

[Jenny Lee 2L]

Along with the periodic table trends for atomic radius, you can think of it like this: Cl has more protons than Na, thus has a greater nuclear charge. Although Cl has more electrons, its electrons are still in the same principal energy level (3) as Na, so its greater nuclear charge has a greater impact. Thus because Cl more protons, the smaller Cl is than Na. However, when Na loses an electron and Cl gains an electron, Na+ now only has a full principal energy level 2, while Cl now has a full principal energy level 3. This drop in principal energy levels for the electrons seems to have a big impact, making Na smaller than Cl.

[Tessa House 3A]

Na is larger than Cl because they have the same number of shells, but Cl has more protons and a higher nuclear charge, which makes it smaller. Na+ has lost its outermost electron and has therefore decreased in size. Cl- has gained an electron and increased in size. Because Na+ lost the electron in its third shell, it has decreased in size significantly and is smaller than Cl-.