dmitri mendeleev
In 1869, a Russian scientist named Dmitri Mendeleev created the periodic table , which is a way of organizing elements according to their unique characteristics, like atomic number, density, boiling point, and other values Figure below . Each element is represented by a one or two letter symbol. For example, H stands for hydrogen, and Au stands for gold. The vertical columns in the periodic table are known as groups, and elements in groups tend to have very similar properties. The table is also divided into rows, known as periods.