The 100+ existing elements  are organized into groups (columns) and periods (rows) of a table known as the Periodic Table.  The familiar looking shape of the table is based upon a number of observations about the elements. One of those properties is the property of mass. There is a general trend (that is broken on only a couple occasions) that the atomic mass of  an element is seen to increase as one progresses across a row and down a column. If you can find a periodic table that has mass information printed on it, you can inspect the values to see the general patter and you can also find the couple of occasions in which the pattern is broken.

Another property is the property of acting like a metal or a nonmetal. The metal elements are grouped together on the table. The same is true of the nonmetal elements. One grouping of metals is known as the Transition Metals. The transition metal block includes the 10 columns of three rows of elements stretching from Group 3 to Group 12.

Learn more about these ideas in the How to Think About This Situation section below.
 

Much of what you need to know to answer this question is discussed in the Fundamentals section above. But if you would like to further your understanding, inspect and study the infographic below on the topic.