Neon (Ne) and sodium (Na) demonstrate vastly different reactivities due to their positions in the periodic table. Sodium is in Group 1 (alkali metals) and is highly reactive because it has one valence electron that it readily loses to form a Na⁺ ion, achieving stability. In contrast, neon is in Group 18 (noble gases) and is chemically inert due to its complete outer shell of eight electrons, making it stable and unlikely to engage in reactions.
Sodium, located in Period 3, has an electron configuration of 1s² 2s² 2p⁶ 3s¹, while neon, in Period 2, has a configuration of 1s² 2s² 2p⁶. The presence of an unpaired electron in sodium encourages its reactivity, whereas the filled valence shell in neon ensures its nonreactivity.
In summary, sodium's high reactivity stems from its single valence electron, while neon's lack of reactivity is due to its complete outer shell, highlighting the fundamental differences between elements in different groups of the periodic table.