Mendeleev’s Table

The types of elements dissolved in seawater affect the properties of the water. Individual elements have unique characteristics, as do the compounds formed by elements that bond with each other. The characteristics of each element allow scientists to predict how it will react, or behave, in the presence of other elements and how it will behave in the presence of water.

In 1869, a chemist named Dmitri Mendeleev (pronounced men-del-AY-ev) published a periodic table based on common physical properties of the 63 elements known at the time (Fig. 2.6). The organization of his table was a powerful tool for understanding how elements behaved. Mendeleev’s periodic table even predicted physical aspects of elements that were not discovered or confirmed until many years later.

The Modern Periodic Table

The modern periodic table includes the 92 naturally occurring elements found in earth’s crust and ocean (in green in Fig. 2.7) and two elements, Technetium (Tc) and Promethium (Pm), which are created as byproducts of nuclear reactors (in orange in Fig. 2.7). In addition to these naturally observed elements, physicists have made over 20 new elements using high-energy accelerators to smash atoms of different elements together at very high speeds (in purple in Fig. 2.7). Elements created this way last for only fractions of a second.