Periodic table of the elements

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Circular periodic table

The periodic table of the elements is a diagrammatic tool to illustrate the scientific theory of periodicity in chemistry, in which the elements have similar properties based on their position on the table. For example, the elements on the far left of the table (Group one) all demonstrate similar properties, such as softness and high reactivity. The table has a lot of predictive power, although there are many exceptions to the periodic properties.

The modern periodic table was first developed by Russian chemist Dimitri Mendeleev. Its layout accurately arranges elements by their electron configuration, atomic number, and chemical properties. Using the structure he created, Mendeleev predicted the existence and properties of several yet-undiscovered elements; when those elements were discovered, his estimates proved to be quite accurate, vindicating his theory which had previously been criticized. Other chemists, such as Antione Lavoisier, and Johann Wolfgang Döbereiner had attempted to create periodic tables by grouping similar elements, but Mendeleev was successful because he left empty spaces for undiscovered, but predicted elements.

Organization

Elements in the periodic table are ordered by number of protons, and rows are arranged by number of electrons in their outermost electron shell. Since farther out shells have more orbitals, this means that there will be more elements in the lower rows of the periodic table than in the higher rows. For example, for principal quantum number n=1, there is only one s-orbital available, which will fit only two electrons (due to the Pauli exclusion principle, which states that no two electrons can have the same quantum numbers). Therefore, only two elements can be in the top row of the periodic table. As the principal quantum number increases, the number of electrons per shell rises, so the farther-down rows hold more elements.

The group number tells how many electrons an element has in its outermost electron shell. For example, every element in group 8A, the noble gases, has its outermost electron shell completely full.


External Links

The Periodic Table

1A 8A
1
H
1.008
2A 3A 4A 5A 6A 7A
2
He
4.003
3
Li
6.939
4
Be
9.0122
5
B
10.811
6
C
12.011
7
N
14.007
8
O
15.999
9
F
18.998
10
Ne
10.183
11
Na
22.99
12
Mg
24.312
3B 4B 5B 6B 7B <--- 8B --> 1B 2B
13
Al
26.982
14
Si
28.086
15
P
30.974
16
S
32.064
17
Cl
35.453
18
Ar
39.948
19
K
39.102
20
Ca
40.08
21
Sc
44.956
22
Ti
47.9
23
V
50.942
24
Cr
51.996
25
Mn
54.938
26
Fe
55.847
27
Co
58.933
28
Ni
58.71
29
Cu
63.546
30
Zn
65.37
31
Ga
69.72
32
Ge
72.59
33
As
74.922
34
Se
78.96
35
Br
79.904
36
Kr
83.8
37
Rb
85.47
38
Sr
87.62
39
Y
88.905
40
Zr
91.22
41
Nb
92.906
42
Mo
95.94
43
Tc
[97]
44
Ru
101.07
45
Rh
102.91
46
Pd
106.4
47
Ag
107.87
48
Cd
112.4
49
In
114.82
50
Sn
118.69
51
Sb
121.75
52
Te
127.6
53
I
126.9
54
Xe
131.3
55
Cs
132.91
56
Ba
137.34
57*
La
138.91
72
Hf
178.49
73
Ta
180.95
74
W
183.85
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.09
79
Au
196.97
80
Hg
200.59
81
Tl
204.37
82
Pb
207.19
83
Bi
208.98
84
Po
210
85
At
210
86
Rn
222
87
Fr
215
88
Ra
226.03
89**
Ac
227.03
104
Rf
[261]
105
Db
[262]
106
Sg
[266]
107
Bh
[264]
108
Hs
[265]
109
Mt
[268]
110
Dt
[271]
111
Rg
[272]
112
Cn
[277]
113
Uut
[284]
114
Fl
[289]
115
Uup
[288]
116
Lv
[292]
117
Uus
[294]
118
Uuo
[294]
 
*Lanthanides
58
Ce
140.12
59
Pr
140.91
60
Nd
144.24
61
Pm
145
62
Sm
150.35
63
Eu
151.96
64
Gd
157.25
65
Tb
158.92
66
Dy
162.5
67
Ho
164.93
68
Er
167.26
69
Tm
168.93
70
Yb
173.04
71
Lu
174.97
 
**Actinides
90
Th
232.04
91
Pa
231
92
U
238.03
93
Np
237.05
94
Pu
239.05
95
Am
241.06
96
Cm
244.06
97
Bk
249.08
98
Cf
252.08
99
Es
252.08
100
Fm
257.1
101
Md
258.1
102
No
259.1
103
Lr
262.11
 
Alkali metals
Alkaline earth metals
Lanthanoids
Actinoids
Transition metals
Other metals
Metalloids
Other nonmetals
Halogens
Noble gases
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