Why do elements in the same group have similar physical and chemical properties?

Why do elements in the same group have similar physical and hemical properties?

" 1.Why do elements of the same group have similar physical and chemical properties "

Why do elements in the same period have different physical and chemical properties? What about elements in the same group?

Why do elements in the same period have different physical and chemical properties? What about elements in the same group?

Why do elements in the same group have similar properties ?

Why the elements belonging to the same group do have similar chemical properties?

Why do all elements of the same group have similar properties?