Let's look at the table another way. There are 18 vertical columns of varying length going across the table. These columns are commonly known as groups, or families of elements. The groups are numbered according to several different conventions, but the most commonly accepted method is the IUPAC (International Union of Pure and Applied Chemistry) system, which labels the groups from left to right with numbers 1 through 18. This is the system we will be using in this Web site. The numbers 1 through 18 are found above the top row of the table for easy reference. We will be looking at some of the groups of the periodic table in more detail later.
So that covers columns and rows. What about individual elements? For that, we have atomic numbers.