Periodic table
| Part of a series on the |
| Periodic table |
|---|
The periodic table of elements, usually shortened to just the periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties, whose structure shows periodic trends. Generally, within one row (period) the elements are metals to the left, and non-metals to the right, with the elements having similar chemical behaviours placed in the same column. Table rows are commonly called periods and columns are called groups. Six groups have accepted names as well as assigned numbers: for example, group 17 elements are the halogens; and group 18 are the noble gases. Also displayed are four simple rectangular areas or blocks associated with the filling of different atomic orbitals.
The organization of the periodic table can be used to derive relationships between the various element properties, but also the predicted chemical properties and behaviours of undiscovered or newly synthesized elements. Russian chemist Dmitri Mendeleev was the first to publish a recognizable periodic table in 1869, developed mainly to illustrate periodic trends of the then-known elements. He also predicted some properties of unidentified elements that were expected to fill gaps within the table. Most of his forecasts proved to be correct. Mendeleev's idea has been slowly expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences.
All the elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been either discovered or synthesized, completing the first seven rows of the periodic table.[1][2] The first 98 elements exist in nature, although some are found only in trace amounts and others were synthesized in laboratories before being found in nature.[n 1] Elements 99 to 118 have only been synthesized in laboratories or nuclear reactors.[3] The synthesis of elements having higher atomic numbers is currently being pursued: these elements would begin an eighth row, and theoretical work has been done to suggest possible candidates for this extension. Numerous synthetic radionuclides of naturally occurring elements have also been produced in laboratories.
Contents
- 1Overview
- 2Grouping methods
- 3Periodic trends and patterns
- 4History
- 5Different periodic tables
- 6Open questions and controversies
- 7See also
- 8Notes
- 9References
- 10Further reading
- 11External links
Overview
hide
| Group | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Alkali metals | Alkaline earth metals | Pnictogens | Chalcogens | Halogens | Noble gases | ||||||||||||||
| Period | |||||||||||||||||||
| 2 | |||||||||||||||||||
| 3 | |||||||||||||||||||
| 4 | |||||||||||||||||||
| 5 | |||||||||||||||||||
| 6 |  | ||||||||||||||||||
| 7 |  | ||||||||||||||||||
| |||||||||||||||||||
| |||||||||||||||||||
1 (red)=Gas 3 (black)=Solid 80 (green)=Liquid 109 (gray)=Unknown Color of the atomic number shows state of matter (at 0 °C and 1 atm)
Standard atomic weight (Ar)[4]
- Ca: 40.078 — Formal short value, rounded (no uncertainty)[5]
- Po: [209] — mass number of the most stable isotope
Background color shows subcategory in the metal–metalloid–nonmetal trend:
| Metal | Metalloid | Nonmetal | Unknown chemical properties | |||||||
| Alkali metal | Alkaline earth metal | Lanthanide | Actinide | Transition metal | Post-transition metal | Reactive nonmetal | Noble gas | |||
Each chemical element has a unique atomic number (Z) representing the number of protons in its nucleus.[n 2] Most elements have differing numbers of neutrons among different atoms, with these variants being referred to as isotopes. For example, carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. Elements with no stable isotopes have the atomic masses of their most stable isotopes, where such masses are shown, listed in parentheses.[6]
In the standard periodic table, the elements are listed in order of increasing atomic number Z (the number of protons in the nucleus of an atom). A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen and selenium are in the same column because they both have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.[7]
No comments:
Post a Comment