The invention of the periodic table of elements is generally credited to Russian Chemist Dimitri Mendeleev in 1869.  There have been many versions of the periodic table and it is recognized as one of the most important tools a chemist can use. 

The table provides information about all the elements, both natural and synthetic.  There are 115 elements - 92 occurring naturally and 23 synthetic.

The elements are organized by increasing atomic number across horizontal rows called periods.

All the elements in a period have the same number of energy levels (orbitals). Every element in the top row (first period) has one orbital for its electrons.  The maximum number of energy levels for any element is seven.

The columns in the periodic table are called groups or families.  The elements in a group have the same number of electrons in their outer energy level.  As a result elements in the same group exhibit similar chemical characteristics.  There are some exception when you look at the transition elements.

The two elements at the top, Hydrogen (H) and Helium (He) also have some exceptions.

For a great website about the Periodic Table - surf to: http://education.jlab.org/itselemental/index.html