(i) Chemical properties depend on the electronic configuration of an atom. Since, isotopes of an element have same atomic number or number of electrons or more precisely same electronic configuration hence, isotopes of an element show similar chemical properties.
(ii) When Rutherford bombarded fast moving a-particles on gold foil he observed that few a-rays were deflected and very few a-rays re-bounded completely. Then, he concluded that nearly all mass of an atom is concentrated within the nucleus and . most of the space in an atom is empty.