However the gradual identification of more and more chemically similar lanthanide elements, whose atomic number was not obvious, led to inconsistency and uncertainty in the periodic numbering of elements at least from lutetium (element 71) onward (hafnium was not known at this time).
haʊˈɛvɚ ðə ɡɹˈædʒuːəl aɪdˈɛntɪfɪkˈeɪʃən ʌv mˈoːɹ ænd mˈoːɹ kˈɛmɪkli sˈɪmɪlɚ lˈænθɐnˌaɪd ˈɛlɪmənts, hˌuːz ɐtˈɑːmɪk nˈʌmbɚ wʌz nˌɑːt ˈɑːbviəs, lˈɛd tʊ ɪŋkənsˈɪstənsi ænd ʌnsˈɜːtənti ɪnðə pˌiəɹɪˈɑːdɪk nˈʌmbɚɹɪŋ ʌv ˈɛlɪmənts æt lˈiːst fɹʌm luːtˈiːɾiəm ˈɛlɪmənt sˈɛvənti wˈʌn ˈɑːnwɚd hˈæfniəm wʌz nˌɑːt nˈoʊn æt ðɪs tˈaɪm.