A periodic table is a tabular display of elements organized by their
atomic numbers, electron configurations, and chemical properties.
LEARNING OBJECTIVES [ edit ]
Describe arrangement of elements in the periodic table
Explain how properties of elements vary within groups
Explain how properties of elements vary across periods
KEY POINTS [ edit ]
A periodic table is a useful framework for analyzing chemical behavior. Such tables are widely
used in chemistry and other sciences.
A group, or family, is a vertical column in the periodic table. Groups usually have more significant
periodic trends than doperiods and blocks.
A period is a horizontal row in the periodic table. Elements in the same period show trends in
atomic radius, ionizationenergy, electron affinity, and electronegativity.
TERMS [ edit ]
electron affinity
the amount of energy released when an electron is added to a neutral atom or molecule to form a
negative ion
atomic orbital
The quantum mechanical behavior of an electron in an atom describing the probability of the
electron's particular position and energy.
ionization energy
the amount of energy required to remove an electron from an atom or molecule in the gas phase
Give us feedback on this content: FULL TEXT [edit ]
The periodic table is a tabular display of
the chemical elements. The elements are
organized based on their atomic numbers,
electron configurations, and recurring
chemical properties.
In the periodic table, elements are
presented in order of increasing atomic
number (the number of protons). The
rows of the table are called periods; the
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columns of the s- (columns 1-2 and He), d(columns 3-12), and p-blocks (columns 13-18, except He) are called groups . (The
terminology of s-, p-, and d- blocks originate from the valence atomic orbitals the element's
electrons occupy. ) Some groups have specific names, such as the halogens or the noble gases.
Since, by definition, a periodic table incorporates recurring trends, any such table can be
used to derive relationships between the properties of the elements and predict the properties
of new, yet-to-be-discovered, or synthesized elements. As a result, the periodic table provides
a useful framework for analyzing chemical behavior, and such tables are widely used in
chemistry and other sciences.
s-block
p-block
1
1s
2
13
2s
3s
4
5
6
7
8
15
16
17
1s
2p
d-block
3
14
18
9
10
11
12
3p
4s
3d
4p
5s
4d
5p
6s
5d
6p
7s
6d
7p
f-block
4f
5f
Blocks in the Periodic Table
A diagram of the periodic table, highlighting the different blocks
History of the Periodic Table
Although precursors exist, Dmitri Mendeleev is generally credited with the publication, in
1869, of the first widely recognized periodic table. Mendeleev designed the table in such a
way that recurring ("periodic") trends in the properties of the elements could be shown.
Using the trends he observed, he even left gaps for those elements that he thought were
"missing. " He even predicted the properties that he thought the missing elements would
have when they were discovered. Many of these elements were indeed later discovered, and
Mendeleev's predictions were proved to be correct.
Groups
Agroup, or family, is a vertical column in the periodic table. Groups usually have more
significant periodic trends than do periods and blocks, which are explained below. Modern
quantum mechanical theories of atomic structure explain group trends by proposing that
elements in the same group generally have the same electron configurations in their valence
(or outermost, partially filled) shell. Consequently, elements in the same group tend to have
shared chemistry and exhibit a clear trend in properties with increasing atomic number.
However, in some parts of the periodic table, such as the d-block and the f-block, horizontal
similarities can be as important as, or more pronounced than, vertical similarities.
Periods
A period is a horizontal row in the periodic table. Although groups generally have more
significant periodic trends, there are regions where horizontal trends are more significant
than vertical group trends, such as in the f-block, where the lanthanides and actinides form
two substantial horizontal seriesof elements. Elements in the same period show trends in
atomic radius, ionization energy, and electron affinity. Atomic radius usually decreases from
left to right across a period. This occurs because each successive element has an added proton
and electron, which causes the electron to be drawn closer to thenucleus, decreasing the
radius.
Group
1
Period
1
1
H
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
2
He
2
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
3
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
4
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
5
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
6
55
Cs
56
Ba
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
7
87
Fr
88
Ra
104
Rf
105
Db
106
Sg
107
Bh
108
Hs
109
Mt
110
Ds
111
Rg
112
Cn
113
Uut
114 115 116 117 118
Fl Uup Lv Uus Uuo
Lanthanides
57
La
58
Ce
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
Actinides
89
Ac
90
Th
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No
103
Lr
The periodic table
Here is the complete periodic table with atomic numbers, groups, and periods. Each entry on the
periodic table represents one element, and compounds are made up of several of these elements.