Is the number of valence electrons the same for all elements within a group on the periodic table?
This is not always true.
For main group elements, the number of valence electrons is the same in every element in the same group.
Group 1 elements have 1 valence electron in the
Group 16 elements have 6 valence electrons in
However, some transition metals don't follow this rule.
For example, let's see the electronic structure of Group 8.