Groups and Periods

1A 2A 3A 4A 5A 6A 7A 8A
(1) (2) (13) (14) (15) (16) (17) (18)
3B 4B 5B 6B 7B — 8B — 1B 2B
(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
1 H He
2 Li Be B C N O F Ne
3 Na Mg Al Si P S Cl Ar
4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
6 Cs Ba La   Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
7 Fr Ra Ac   Rf Db Sg Bh Hs Mt Ds Rg Uub — Uuq — — — —
6   Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
7   Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

 

The Periodic Table of the Elements summarizes a great deal of information about the properties of the chemical elements.

  • Groups:  the vertical columns on the table.  These define a "family" of elements which have similar chemical properties
  • Periods:  the horizontal rows on the table, with the elements arranged in order of increasing atomic number.

Traditionally, in the United States the taller groups on the table (the main group elements) are numbered from IA/1A through VIIIA/8A.  The shorter groups (the transition metals) are numbered from IB/1B through VIIIB/ 8B.  (The use of Roman numerals is more traditional, but in this periodic table I have opted to use Arabic numerals instead because they can be squeezed into a reasonably-sized HTML-based periodic table more easily.)

Unfortunately, that's not the only way to number the columns.  (Chemists like to try to keep things consistent, but they often don't succeed!)   In Europe, the traditional numbering has the left half of the table numbered from Group IA (H) through VIIIA (Ni), and the right half of the periodic table is numbered from Group IB (Cu) through VIIB (F), with the noble gases as Group 0.

In order to resolve this confusion, the International Union of Pure and Applied Chemistry (IUPAC) proposed that the columns on the periodic table be numbered sequentially in Arabic numbers, from 1 to 18.  Although this system has been accepted by the American Chemical Society (ACS), many chemists use the traditional A/B designations instead, since this more accurately reflects the valence of the elements in chemical bonding.

In the periodic tables in this section, I have used the traditional system, numbering the main groups as 1A through 8A, and the transition metals as 1B through 8B.  The IUPAC-approved numbering system is shown in parentheses below the traditional column numbering.  I have offset the labels for the transition metal groups by a couple of spaces to improve the legibility of the table.