existence of several unknown elements Dmitri Mendeleev Modern Periodic Table • Henry G.J. Moseley • Determined the atomic numbers of elements from their X-ray spectra (1914) • Arranged elements by increasing atomic number 1887 - 1915 The Periodic Table On your periodic table, draw the “staircase” starting from Boron. 1 1 IA 1 H 1.00797 2 3 Periodic Table 2 IIA 13 IIIA 4 Li Be 11 12 5 6.939 9.0122 3 Na Mg 22.9898 24.305 4 19 20 3 IIIB 21 4 IVB 5 VB 22 23 K Ca Sc Ti…
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