The complete electron configuration of lithium is 1s² 2s¹.
Let's break down the notation:
The "1s²" part represents the first energy level (or shell) and indicates that there are two electrons in the 1s orbital. The "1s" orbital is the closest to the nucleus and can hold a maximum of two electrons.
The "2s¹" part represents the second energy level (or shell) and indicates that there is one electron in the 2s orbital. The "2s" orbital is in the second energy level and can also hold a maximum of two electrons, but in the case of lithium, only one electron is present.
In summary, lithium has three electrons, with two of them occupying the 1s orbital and one occupying the 2s orbital.