Indeed, the similarity is so great that it is quite difficult to separate potassium, rubidium, and caesium, due to their similar ionic radii; lithium and sodium are more distinct.
ˌɪndˈiːd, ðə sˌɪmɪlˈæɹᵻɾi ɪz sˌoʊ ɡɹˈeɪt ðˌɐɾɪt ɪz kwˈaɪt dˈɪfɪkəlt tə sˈɛpɚɹˌeɪt pətˈæsiəm, ɹuːbˈɪdiəm, ænd sˈiːsiəm, dˈuː tə ðɛɹ sˈɪmɪlɚɹ aɪˈɑːnɪk ɹˈeɪdɪˌaɪ; lˈɪθiəm ænd sˈoʊdiəm ɑːɹ mˈoːɹ dɪstˈɪŋkt.