Electronegativity decreases moving down a group because adding an electron shell pushes the valence electrons further from the nucleus. Atomic radius increases moving down a group, as successive elements gain an electron energy level. Elements within a group display a pattern with respect atomic radius, electronegativity, and ionization energy. Elements with a group share a valence electron configuration. Groups are numbered from 1 (the alkali metals) to 18 (the noble gases). The columns of elements are called groups or families. Moving down a period on the table adds a new electron shell. Elements toward the left side of a period are metals, while those on the right side are nonmetals. Element atomic number increases moving from left to right across a period. There are seven rows of the periodic table, which are called periods. The structure of the periodic table makes it possible to see relationships between elements at a glance and predict properties of unfamiliar, newly discovered, or undiscovered elements. However, his table illustrated recurring trends or periodicity in the element properties. Mendeleev’s table ordered the elements according to increasing atomic weight rather than atomic number.

The modern table is derived from Mendeleev’s periodic table, but with one significant different.

The Russian scientist Dmitri Mendeleev is most often credited with inventing the periodic table (1869). The periodic table is a tabular arrangement of the chemical elements by increasing atomic number which displays the elements so that one may see trends in their properties.

Groups on periodic table color coded