Periodic Table

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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, are more usually aspergic types who 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 distressing 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 round 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 somewhere around 120. 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
Aluminium
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
* 58
Hf
Hafnium
59
Ta
Tantalum
60
W
Tungsten
61
Re
Rhenium
62
Os
Osmium
63
Ir
Iridium
64
Pt
Platinum
65
Au
Gold
66
Hg
Mercury
67
Tl
Thallium
68
Pb
Lead
69
Bi
Bismuth
70
Po
Polonium
71
At
Astatine
72
Rn
Radon
7 73
Fr
Francium
74
Ra
Radium
** 76
Rf
Rutherfordium
77
Db
Dubnium
78
Sg
Seaborgium
79
Bh
Bohrium
80
Hs
Hassium
81
Mt
Meitnerium
82
Ds
Darmstadtium
83
Rg
Roentgenium
84
Cn
Copernicium
85
Nh
Nihonium
86
Fl
Flerovium
87
Mc
Moscovium
88
Lv
Livermorium
89
Tn
Tennessine
90
Og
Oganesson

* 91
La
Lanthanum
92
Ce
Cerium
93
Pr
Praseodymium
94
Nd
Neodymium
95
Pm
Promethium
96
Sm
Samarium
97
Eu
Europium
98
Gd
Gadolinium
99
Tb
Terbium
100
Dy
Dysprosium
101
Ho
Holmium
102
Er
Erbium
103
Tm
Thulium
104
Yb
Ytterbium
105
Lu
Lutetium
** 106
Ac
Actinium
107
Th
Thorium
108
Pa
Protactinium
109
U
Uranium
110
Np
Neptunium
111
Pu
Plutonium
112
Am
Americium
113
Cm
Curium
114
Bk
Berkelium
115
Cf
Californium
116
Es
Einsteinium
117
Fm
Fermium
118
Md
Mendelevium
119
No
Nobelium
120
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."