The modern periodic table is arranged in ascending order according to atomic number. An element's atomic number is equal to the number of protons in each atom. Within this order, elements are arranged into distinct group... More »

The modern periodic table is based upon the atomic number and the physical properties of each element. The periods, or rows, are arranged by increasing atomic number. Each column, or group, of elements has similar physic... More »

Henry Moseley's discovery of the atomic number refined the way elements are listed in the periodic table. Prior to his discovery, the elements were listed by atomic mass. Chemists considered the atomic numbers to be some... More »

"Rn" stands for radon in the periodic table. Radon's atomic number is 86, and its atomic weight is 222. Radon was originally called niton when it was discovered in 1900. More » Science Chemistry

The lightest element on the periodic table is hydrogen. The atomic weight of hydrogen is 1.00794 and the atomic number is 1. Hydrogen is the most abundant element on the periodic table with 75 percent of the mass of the ... More »

The periodic table was invented by chemist Dmitri Mendeleev to organize and compare elements and understand their relations with each other. Mendeleev created the periodic table between 1868 and 1870 while writing his bo... More »

The periodic table was built to show the relationships among the various elements. The periodic table was constructed in 1869 by Dmitri Mendeleev. More »