One of the many ways scientists classify substances is by the periodic table. Our current periodic table is a chart showing the elements in order by increasing atomic number and grouped by their similar qualities. In the late 1800s, Russian chemist Dimitri Mendeleev was believed to be the first to place the elements in order by their increasing atomic masses. Mendeleev realized that the repeating patterns he saw were grouping the elements by their properties, and he even went so far as to leave spaces for elements that had not yet been discovered.
Journal Entry # 5
a) Which two of the following elements should show the most similarities:
C, Se, Xe, Si, Ag, and Mg?
b) Why did it turn out to be better to place elements in order on the
periodic table by atomic number instead of atomic mass?