Structure of the periodic table Tamil revision mind map drawn as the table's own silhouette shape divided into four coloured blocks: the s-block groups 1 and 2 on the left with valence configuration ns1 or ns2, the p-block groups 13 to 18 on the right with valence ns2np1 to np6, the d-block transition metals groups 3 to 12 in the middle starting from period 4, and the detached f-block lanthanides and actinides below, with periods as the seven horizontal rows numbered by highest occupied shell and groups as the eighteen vertical columns sharing identical outer-shell configuration, plus the history from Mendeleev's 1869 atomic-mass ordering to Moseley's 1913 correction to atomic number.