What is the Periodic Table?
The periodic table of elements is a tabular display of chemical elements organized on the basis of their atomic number (number of protons in the nucleus), electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number. The standard form of the table includes periods (horizontal rows) and groups (vertical columns).
History of the Periodic Table
The development of the periodic table is one of the great stories in science:
- 1789 - Antoine Lavoisier published first list of elements
- 1862 - Alexandre-Emile Béguyer de Chancourtois arranged elements by atomic weight in a helical arrangement
- 1864 - John Newlands noticed that elements with similar properties recurred at every eighth element (Law of Octaves)
- 1869 - Dmitri Mendeleev published the first widely recognized periodic table, leaving gaps for undiscovered elements and correctly predicting their properties
- 1913 - Henry Moseley determined that atomic number, not atomic weight, was the organizing principle
- 2016 - Four new elements (113, 115, 117, 118) were officially added, completing period 7
Organization of the Periodic Table
Periods (Rows)
There are 7 periods in the modern periodic table. Moving across a period from left to right, the atomic number increases by one, and elements transition from metals to metalloids to nonmetals.
Groups (Columns)
There are 18 groups. Elements in the same group have the same number of valence electrons and therefore similar chemical properties. Key groups include:
- Group 1: Alkali metals (Li, Na, K, Rb, Cs, Fr)
- Group 2: Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra)
- Group 17: Halogens (F, Cl, Br, I, At)
- Group 18: Noble gases (He, Ne, Ar, Kr, Xe, Rn)
How to Read an Element Box
Each element box in the periodic table contains: the atomic number (top), element symbol (center), element name (bottom), and atomic mass (below name). Additional information like electron configuration and oxidation states may also be shown.