Humans have had a strong interest in classifying and working with matter throughout recorded history. Many of the elements that we are familiar with today have been known since ancient times, such as gold (aurum), silver (argentum), potassium (kalium), sodium (natrium), lead (plumbum), and copper (cuprium). An element’s reactivity, solubility, flame color, compound formation, and luster are just a few of the various characteristics that people have studied and attempted to categorize. We can use our knowledge of atomic number and atomic weight in conjunction with these characteristics to arrange the elements systematically. In fact, this was how the first versions of the periodic table were created in the mid-1800s. Our modern day periodic table, pictured above, is an evolution of these earlier works. In this chapter, we will be studying how the periodic table of elements is organized and how it can be used to predict certain properties about a given element.