Periodic Table
. Periodic Table, table of the chemical elements arranged to illustrate patterns of recurring chemical and physical properties. Elements, such as oxygen, iron, and gold, are the most basic chemical substances and cannot be broken down by chemical reactions . All other substances are formed from combinations of elements. The periodic table provides a means of arranging all the known elements and even those yet to be discovered. See Alphabetic list of Chemical Elements ARRANGEMENT OF THE TABLE The elements within the modern periodic table are arranged from left to right, top to bottom, in order of increasing atomic number. An element’s atomic number is the number of protons in its nucleus. There are 92 naturally occurring elements, ranging from hydrogen, which has atomic number 1, to uranium, whose atomic number is 92. The periodic table also includes artificially created elements, whose atomic numbers are higher than 92. These additions must be prepared through nuclear reactions. The