The least number of valence electrons an atom can have is zero. Valence electrons are the electrons in the outermost energy level, or valence shell, of an atom. In some cases, such as the noble gases, atoms have a full valence shell with eight electrons (except for helium, which has two). These elements are stable and less likely to form chemical bonds. However, certain elements, such as hydrogen and helium, have only one or two electrons respectively in their valence shells. So, the least number of valence electrons an atom can have is zero, as in the case of helium, which has a filled valence shell with only two electrons.