What Is The Periodic Table?

The Periodic Table is a large table or chart that contains all the known chemical elements. It is arranged in order of the atomic number of the elements. The atomic number of an element is the number of protons that it has in its nucleus. The number of protons is always the same as the number of electrons that orbit around the nucleus.

When the elements are arranged in this way, and are put into a pattern that matches up elements with similar chemical properties, the result is the well known periodic table. The table has columns, called groups and rows, called periods. Today's periodic table has 8 groups but has special sections for the transition elements and for the radioactive elements, the lanthanides and the actinides.

Hydrogen, which has an atomic number of 1 does not really fit into any of the groups, so is the first element, placed in its own period at the head of Group I.