I really think this article is quite confused in its basic definition! 

The article starts off "In chemistry, periodic trends are the tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements."  This seems completely wrong-headed to me, and completely misunderstands both the common and scientific meanings of the word "periodic", and why the "periodic" table is so called! "Periodic" things are those which repeat themselves at regular intervals. The "periodic trends" which Mendelev famously noted in the elements (when arranged in increasing atomic weight) were recurring similar properties. It was on the basis of these recurrances that Mendelev decided where to break the table into a new column or row. In other words, the "definition" in the article is ass backwards.