Elements which are similar as regards their chemical properties have atomic weights which are either of nearly the same value (eg. Pt, Ir, Os) or which increase regularly (eg. K, Ru, Cs).
1564 - 1616
1803 – 1882
1854 – 1900
1942 – 2016
1928 – 2014
1835 – 1910
1869 – 1948
1884 – 1962
1898 – 1963
1929 – 1993
1879 – 1955
1809 – 1865
