Lithium, with an atomic number of 3, has two electrons in the first shell - its K shell - and one electron in the second shell - its L shell. The single valence electron of lithium is in the 2s orbital. This outermost electron is loosely held by the nucleus, making lithium highly reactive.

When lithium atom loses one of its valence electron, it becomes a lithium ion with a positive charge of 1 (Li+). This results from the removal of the outermost electron, which leaves behind the two electrons in the K shell and an empty space in the L shell.