Periodic Table

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It matters
Chemistry
Icon chemistry.png
Action and reaction
Elementary!
Spooky scary chemicals
Er, who's got the pox?
For more information, see: List of elements in the periodic table
There's antimony, arsenic, aluminum, selenium

And hydrogen and oxygen and nitrogen and rhenium
And nickel, neodymium, neptunium, germanium
And iron, americium, ruthenium, uranium
Europium, zirconium, lutetium, vanadium
And lanthanum and osmium and astatine and radium
And tantalum, technetium, titanium, tellurium

And cadmium and calcium and chromium and curium...
Tom Lehrer, The Elements

The Periodic Table is a chart which organises chemical elements into groups based on their various properties — ascending by atomic number and grouped by things such as reactivity and valency. While it was first organised by these macroscopic properties, it actually forms a map of the atomic orbital structure indicating how quantum mechanical concepts relate to chemical properties. The Table was invented by Russian chemist Dmitri Mendeleyev in the second half of the 19th century, though others were part of a push towards order in the chemical world.

Origins[edit]

Chemical behaviour is generally very messy, complicated, and irregular.[1] Chemists, in contrast, enjoy making neat and tidy lists of things. By the 17th century, chemists had begun to use the concept of an "element" in its modern sense (i.e. a substance which cannot be broken down into a simpler substance using chemical means) — which was nice and tidy — but, distressingly, they had also begun to discover dozens of new elements besides those which had been known for centuries — this was distressingly untidy. A glimmer of hope was at hand, however: it was noticed that many of these newly discovered elements appeared to exhibit similar properties, seeming almost to belong to 'families'. Moreover, these similar properties often seemed to exhibit trends when the elements were placed in order of atomic weight. Examples included "triads" such as chlorine, bromine, and iodine, and copper, silver, and gold.

The race was on amongst chemists to draw up some kind of nice tidy list which would arrange the ever-increasing numbers of these pesky new elements in some kind of elegant way which brought order to the increasing chemical mess. The breakthrough was finally made by Mendeleev. His Table managed to set out the elements in rows and columns, in order (more or less) of atomic weight, so that those elements with similar properties fell into nice tidy vertical groups. Mendeleev made two particular innovations over previous pedants:

  • in a couple of cases where listing the elements in order of atomic weight would have messed up his groups, he swapped elements around so that they fitted the pattern
  • in further cases where listing the elements in any order wouldn't fit the pattern at all, he declared there must be a "missing element" and left a gap for it in the table.

However, Mendeleev couldn't, at the time, provide any physical explanation of why there should be missing elements, or why atomic weights occasionally needed swapping around. The trends were evident, but the knowledge of atomic structure and the identity of the missing elements was still far off, meaning that there was no verifiable proof that the periodic table was as Mendeleev hypothesised. Still, he stuck to his hypothesis, and the testable predictions of what properties these missing elements ought to have if and when they were discovered. Luckily for him, his predictions were correct!

Later, the discovery of atomic structure (protons, neutrons, and electrons) provided a sound rationalising for Mendeleev's quirky ad hoc tweaks, and vindicated his periodic table. It was discovered that the shared properties of similar elements was due to these their having the same number of electrons in their outer shells. Thus, silicon has similar reactivities to carbon, although their difference in physical size also affects these properties. These observed facts are combined in their arrangement in the modern Periodic Table of the Elements.

Elements in the table are sorted by the increasing number of protons in their nuclei, from 1 to 118. There is no necessary reason for the number of elements to end there, but heavier elements would have half-lives in minute fractions of a millisecond, so they'd be very difficult to detect. However, similarly to what Mendeleev did, it is possible to predict the properties of these hypothetical elements using both periodic trends and our current understanding of physics. The structure of the table is based on the electronic structure of the atom: in the "p" block for example, there are elements for which the outermost electron is in a "p" orbital.

And here it is![edit]

Group # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Period
1 1
H
Hydrogen
2
He
Helium
2 3
Li
Lithium
4
Be
Beryllium
5
B
Boron
6
C
Carbon
7
N
Nitrogen
8
O
Oxygen
9
F
Fluorine
10
Ne
Neon
3 11
Na
Sodium
12
Mg
Magnesium
13
Al
Aluminum
14
Si
Silicon
15
P
Phosphorus
16
S
Sulfur
17
Cl
Chlorine
18
Ar
Argon
4 19
K
Potassium
20
Ca
Calcium
21
Sc
Scandium
22
Ti
Titanium
23
V
Vanadium
24
Cr
Chromium
25
Mn
Manganese
26
Fe
Iron
27
Co
Cobalt
28
Ni
Nickel
29
Cu
Copper
30
Zn
Zinc
31
Ga
Gallium
32
Ge
Germanium
33
As
Arsenic
34
Se
Selenium
35
Br
Bromine
36
Kr
Krypton
5 37
Rb
Rubidium
38
Sr
Strontium
39
Y
Yttrium
40
Zr
Zirconium
41
Nb
Niobium
42
Mo
Molybdenum
43
Tc
Technetium
44
Ru
Ruthenium
45
Rh
Rhodium
46
Pd
Palladium
47
Ag
Silver
48
Cd
Cadmium
49
In
Indium
50
Sn
Tin
51
Sb
Antimony
52
Te
Tellurium
53
I
Iodine
54
Xe
Xenon
6 55
Cs
Caesium
56
Ba
Barium
* 72
Hf
Hafnium
73
Ta
Tantalum
74
W
Tungsten
75
Re
Rhenium
76
Os
Osmium
77
Ir
Iridium
78
Pt
Platinum
79
Au
Gold
80
Hg
Mercury
81
Tl
Thallium
82
Pb
Lead
83
Bi
Bismuth
84
Po
Polonium
85
At
Astatine
86
Rn
Radon
7 87
Fr
Francium
88
Ra
Radium
** 104
Rf
Rutherfordium
105
Db
Dubnium
106
Sg
Seaborgium
107
Bh
Bohrium
108
Hs
Hassium
109
Mt
Meitnerium
110
Ds
Darmstadtium
111
Rg
Roentgenium
112
Cn
Copernicium
113
Nh
Nihonium
114
Fl
Flerovium
115
Mc
Moscovium
116
Lv
Livermorium
117
Tn
Tennessine
118
Og
Oganesson

* 57
La
Lanthanum
58
Ce
Cerium
59
Pr
Praseodymium
60
Nd
Neodymium
61
Pm
Promethium
62
Sm
Samarium
63
Eu
Europium
64
Gd
Gadolinium
65
Tb
Terbium
66
Dy
Dysprosium
67
Ho
Holmium
68
Er
Erbium
69
Tm
Thulium
70
Yb
Ytterbium
71
Lu
Lutetium
** 89
Ac
Actinium
90
Th
Thorium
91
Pa
Protactinium
92
U
Uranium
93
Np
Neptunium
94
Pu
Plutonium
95
Am
Americium
96
Cm
Curium
97
Bk
Berkelium
98
Cf
Californium
99
Es
Einsteinium
100
Fm
Fermium
101
Md
Mendelevium
102
No
Nobelium
103
Lr
Lawrencium


Metals Metalloids Nonmetals Unknown
chemical
properties
Alkali metals Alkaline earth metals Inner transition metals Transition metals Post-transition metals Other nonmetals Halogens Noble gases
Lanthanides Actinides

External links[edit]

References[edit]

  1. More specifically:
    • Inorganic Chemist: "Inorganic chemistry is messy, complicated and irregular and therefore interesting. Organic chemistry is boring and predictable."
    • Organic Chemist: "Organic chemistry is messy, complicated and irregular and therefore interesting. Inorganic chemistry is boring and predictable."