* Number of valence electrons: Both lithium and sodium have one valence electron in their outermost shell. This is the defining characteristic of alkali metals and is responsible for their similar reactivity.
* Electron configuration: Both elements have a single electron in their outermost s-orbital.
* Lithium: 1s² 2s¹
* Sodium: 1s² 2s² 2p⁶ 3s¹
* Similar reactivity: Due to their single valence electron, both elements readily lose this electron to form a +1 cation, making them highly reactive. This reactivity is also reflected in their similar chemical properties, such as their tendency to react violently with water.
However, it's important to note that their electronic configurations are not identical. Sodium has additional filled electron shells compared to lithium, which leads to a larger atomic radius and weaker attraction between the nucleus and valence electron. This accounts for the decreasing reactivity of alkali metals as you move down the group.
