Question

does all elements have the same number of valence electrons

Answer 1

The elements that have the same number of valence electrons are located in a group.
The group number from the Periodic table relates to the number of electrons in the valence shell.
For example, elements in group 1 (H, Na, Li, K, Rb, Cs, Fr) all have 1 valence electrons and elements in group 7 (Cl, F, I, Br) have 7 valence electrons in its outer shell.