What is a periodic table? What is its importance?

The Periodic Table provides the names, atomic numbers, symbols and atomic weights of known elements. It serves as a great tool for solving chemistry problems.

A periodic table is divided into groups (columns), where elements with each group behave similarly while bonding with other elements; and periods (rows), where elements in one period have same number of electron shells.The periodic table is important because it is organized to provide a great deal of information about elements and how they relate to one another in one reference. The table can be used to predict the properties of all the elements, even those that have not yet been discovered

Earlier Mendeleev's Periodic Table was based on atomic mass but the Modern Periodic Table is based on atomic number.