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Grouping methods


A group or family is a vertical column in the periodic table. Groups usually have more significant periodic trends than periods and blocks, explained below. Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell.Consequently, elements in the same group tend to have a 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.
Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases) Previously, they were known by roman numerals. In America, the roman numerals were followed by either an "A" if the group was in the s- or p-block, or a "B" if the group was in the d-block. The roman numerals used correspond to the last digit of today's naming convention (e.g. the group 4 elements were group IVB, and the group 14 elements were group IVA). In Europe, the lettering was similar, except that "A" was used if the group was before group 10, and "B" was used for groups including and after group 10. In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new IUPAC naming system was put into use, and the old group names were deprecated.

Some of these groups have been given trivial (unsystematic) names, as seen in the table below, although some are rarely used. Groups 3–10 have no trivial names and are referred to simply by their group numbers or by the name of the first member of their group (such as "the scandium group" for Group 3), since they display fewer similarities and/or vertical trends.
Elements in the same group tend to show patterns in atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group has a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus. There are exceptions to these trends, however, an example of which occurs in group 11 where electronegativity increases farther down the group.
Groups in the periodic table

Group numbera 1 2 3d 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
CAS (US,
pattern A-B-A) IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA VIIIA
old IUPAC (Europe,
pattern A-B) IA IIA IIIA IVA VA VIA VIIA VIII IB IIB IIIB IVB VB VIB VIIB Group
0
Trivial name Alkali metals Alkaline earth metals Coin­age metalse Vola­tile metalse Icosa­gense Crys­tallo­gense Pnicto­gens Chal­co­gens Halo­gens Noble gases
Name by element Lith­ium group Beryl­lium group Scan­dium group Titan­ium group Vana­dium group Chro­mium group Man­ga­nese group Iron group Co­balt group Nickel group Cop­per group Zinc group Boron group Car­bon group Nitro­gen group Oxy­gen group Fluor­ine group Helium or Neon group
Period 1
H
c
He
Period 2
Li
Be
B
C
N
O
F
Ne
Period 3
Na
Mg
Al
Si
P
S
Cl
Ar
Period 4
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Period 5
Rb
Sr
Y
d
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Period 6
Cs
Ba
La
d Ce–Lu
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Period 7
Fr
Ra
Ac
d Th–Lr
Rf
Db
Sg
Bh
Hs
Mt
Ds
Rg
Cn
Nh
Fl
Mc
Lv
Ts
Og
a Current, modern IUPAC group number.
b The noble gases had not yet been discovered at the time of Mendeleev's original table. Later (1902), Mendeleev accepted the evidence for the existence of the noble gases, and placed them in a separate "group 0".
c Hydrogen (H), while placed in column 1, is not considered to be in the group alkali metals.
d Group 3: Depending on the source, the entries below scandium and yttrium in this group include lutetium (Lu) and lawrencium (Lr), or lanthanum (La) and actinium (Ac), or the whole set of 15 lanthanides and 15 actinides. IUPAC has initiated a project to choose between the first two possibilities, so that the recommended definition of Group 3 will be either (1) the elements Sc, Y, Lu and Lr, or (2) the elements Sc, Y, La and Ac.
e This group name is not recommended by IUPAC.
Periods

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