- The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations (electron shell model), and recurring chemical properties. Elements are presented in the increasing order of their atomic number (the number of protons present in the nucleus of an atom).
- Dmitri Mendeleev is generally credited with the publication of the first periodic table which contained the then-known elements and also predicted some properties of then-unknown elements that would be expected to fill gaps in this table. This was proved correct when the elements in question were subsequently discovered.
- Mendeleev’s periodic table has since been expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behavior. Properties of an element can be predicted on the basis of its location in the periodic table.
- Elements from atomic numbers 1 to 118 have been discovered or reportedly synthesized, of which First 98 elements exist naturally although some are found only in trace amounts and were synthesized in laboratories before being found in nature. Uranium, with 92 protons, is the heaviest naturally occurring element.
- Elements with atomic numbers from 99 to 118 have only been synthesized, or claimed to be so, in laboratories of which elements 113, 115, 117, and 118 are yet to be confirmed.