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
Chemical
Series of the Periodic Table
| Alkali
metals |
Alkaline
earths |
Lanthanide |
Actinides |
Transition
metals |
| Poor
metals |
Metalloids |
Nonmetals |
Halogens |
Noble
gases |
- 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).
Groups
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.
Group numbers
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.
Explanation
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
properties.
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) and bromine (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 highly colored.
History
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:
| Some triads |
| Element |
|
Atomic mass |
Density |
| chlorine |
|
35.5 |
0.00156 g/cm3 |
| bromine |
|
79.9 |
0.00312 g/cm3 |
| iodine |
|
126.9 |
0.00495 g/cm3 |
|
|
| calcium |
|
40.1 |
1.55 g/cm3 |
| strontium |
|
87.6 |
2.6 g/cm3 |
| barium |
|
137 |
3.5 g/cm3 |
|
|
|
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.
