Co-Authored By:
Hydrogen has 1 electron in the first shell (so one valence electron). Helium has 2 electrons --- both in the first shell (so two valence electrons). Lithium has 3 electrons --- 2 in the first shell, and 1 in the second shell (so one valence electron).
Keeping this in consideration, does lithium have valence electrons?
Lithium has atomic number of 3. So a neutral lithium atom has 3 protons and 3 electrons. Two electrons in shell 1 and one electron in shell 2. So Lithium has only 1 valence electron in the 2s orbital.
Beside above, why is 3rd shell 8 or 18?
Each shell can contain only a fixed number of electrons: The first shell can hold up to two electrons, the second shell can hold up to eight (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on. For an explanation of why electrons exist in these shells see electron configuration.
5 valence electrons