table of the chemical elements
is a tabular display of the known chemical
elements. The elements are arranged by electron structure so that many chemical
properties vary regularly across the table. Each element is listed by its atomic
number and chemical symbol.
The standard table provides the necessary basics.
There are also other methods for displaying the chemical elements for more details
or different perspectives.Standard periodic table
Color coding for atomic numbers
Series of the Periodic Table
- Elements numbered in blue are liquids
at standard temperature and pressure (STP);
- those in green
are gases at STP;
- those in black are solid at STP;
- those in red are synthetic (all are solid at STP).
- those in gray have not yet been
discovered (they also have muted fill colors indicating the likely chemical series
they would fall under).
A group is a vertical column in the periodic table of the elements.
There are 18 groups in the standard periodic table. Elements in
a group have similar configurations of their valence shell electrons,
which gives them similar properties.
There are three systems of group numbers; one using Arabic numerals
and the other two using Roman numerals. The Roman numeral names
are the original traditional names of the groups; the Arabic numeral
names are a newer naming scheme recommended by International Union
of Pure and Applied Chemistry (IUPAC). The IUPAC scheme was developed
to replace both older Roman numeral systems as they confusingly
used the same names to mean different things.
of the structure of the periodic table
The number of electron shells
an atom has determines what period it belongs to. Each shell is
divided into different subshells, which as atomic number increases
are filled in roughly this order:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 8s 5g 6f 7d 8p ...
Hence the structure of the table. Since the outermost electrons determine chemical
properties, those tend to be similar within groups. Elements adjacent
to one another within a group have similar physical properties,
despite their significant differences in mass. Elements adjacent
to one another within a period have similar mass but different
For example, very near to nitrogen (N)
in the second period of the chart are carbon (C) and
oxygen (O). Despite
their similarities in mass (they differ by only a few atomic mass
units), they have extremely different properties, as can be seen
by looking at their allotropes: diatomic oxygen is a gas that
supports burning, diatomic nitrogen is a gas that does not support
burning, and carbon is a solid which can be burnt (yes, diamonds
can be burnt!).
In contrast, very near to chlorine (Cl)
in the next-to-last group in the chart (the halogens) are fluorine (F)
(Br). Despite their dramatic differences in mass within the group,
their allotropes have very similar properties: They are all highly
corrosive (meaning they combine readily with metals to form metal
halide salts); chlorine and fluorine are gases, while bromine
is a very low-boiling liquid; chlorine and bromine at least are
History of the periodic table
The original table was created without a knowledge of the inner
structure of atoms:
if one orders the elements by atomic mass, and then plots certain
other properties against atomic mass, one sees an undulation or
periodicity to these properties as a function of atomic
mass. The first to recognize these regularities was the German
chemist Johann Wolfgang Döbereiner who, in 1829, noticed a number
of triads of similar elements:
This was followed by the English chemist John Alexander Reina
Newlands, who in 1865 noticed that the elements of similar type
recurred at intervals of eight, which he likened to the octaves
of music, though his law of octaves was ridiculed by
his contemporaries. Finally, in 1869, the German Lothar Meyer
and the Russian chemist Dmitry Ivanovich Mendeleev almost simultaneously
developed the first periodic table, arranging the elements by
mass. However, Mendeleev plotted a few elements out of strict
mass sequence in order to make a better match to the properties
of their neighbours in the table, corrected mistakes in the values
of several atomic masses, and predicted the existence and properties
of a few new elements in the empty cells of his table. Mendeleev
was later vindicated by the discovery of the electronic structure
of the elements in the late 19th and early 20th century.
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