`  =``There are no periodic trends``= This section/sentence is a bit wrong headed.  Periodic trends are those which repeat from period to period (e.g. noble gas behavior recurring). What this really means to talk about is ``horizontal trends`` across the period. What the article means to say, I guess, is that horizontal trends are due to a quantum shell filling, and since 1s fills within 2 electrons, there's not much scope to look at 'trends'. It's also perhaps worth noting that when Mendelev put the ``periodic`` table together, he didn't know the noble gases existed, so all he had to place from what would become period 1 was hydrogen.  `