Neon (Ne) and sodium (Na) have vastly different reactivities due to their positions in the periodic table. Sodium is located in Group 1, known as alkali metals, and is highly reactive due to its single valence electron, which it readily loses to form a Na⁺ ion and achieve stability. In contrast, neon is in Group 18, the noble gases, and is chemically inert because it has a full outer shell of eight electrons, fulfilling the octet rule and making it unlikely to engage in chemical reactions.
Sodium, found in Period 3, has the electron configuration 1s² 2s² 2p⁶ 3s¹. Its lone 3s electron contributes to its reactivity. Neon, in Period 2, possesses a stable electron configuration of 1s² 2s² 2p⁶, which results in its nonreactive nature.
Overall, sodium's reactivity stems from its incomplete valence shell, while neon’s stability arises from its complete outer shell, illustrating key differences between elements in different groups of the periodic table.