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 s fills within 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 was hydrogen