Periodic table of elements

 Introduction

 History of periodic table

The discovery of chemical elements has been ongoing since ancient times. Certain elements, such as gold (Au), appear in nature in elemental form and were thus discovered thousands of years ago. In contrast, some elements, such as technetium (Tc), are radioactive and intrinsically unstable and were discovered after the development of technology during the twentieth century.

As the number of known elements increased, scientists began classifying them. In 1869, Dmitri Ivanovich Mendeleev in Russia and Lothar Meyer in Germany published nearly identical classification schemes

Both noted that similar chemical and physical properties occur periodically when the elements are arranged in order of increasing atomic mass. Scientists at that time had noknowledge of atomic numbers.However with the introduction of the concept of atomic number the modern periodic table was

constructed.