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 »

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The vertical columns on the period table are called groups. There are 18 groups on the periodic table, and elements that are members of the same group share similar traits. More »

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 »

There are at least 76 solid elements in the periodic table. Eleven elements are gases at room temperature, while only three are liquids. Only the first 98 elements in the periodic table exist in nature. More »