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Table of Contents
Front Page
Aufbau Periodic Table  
also available as pdf file at:
Condensed Periodic Table   also available as pdf file at:
Description of Table
Periodic Table Links
Periodic Table with Element Colors (traditional) 
above also available as pdf files at:, 
Some periodic table questions and unresolved issues




      Science has aptly been described as a search for order in the Universe.  It follows that chemistry is a search for order in matter. While the search will always be a work in progress, great strides towards the finding of order in matter resulted in 1869 when Dimitri Mendeleev stood on the shoulders of many others and published his periodic table [1]. The table has since been modified and improved but still has a remarkable resemblance to the original Mendeleev table [2].  Excellent compilations of many alternate periodic tables have been published that use novel and intriguing approaches (e.g., circles, spirals and 3d) [3], but the contemporary versions of the Mendeleev table are the charts found on the walls of thousands of lecture rooms around the world.  The periodic table deserves recognition as one of the milestones of science along with contributions from other sciences including but not limited to:  physics by Newton and Einstein, biology by Darwin, Rosalind Franklin, Watson and Crick, astronomy by Copernicus and Galileo and geology by Wegener.

     The periodic table arranges the 118 known elements according to increasing atomic number and lines up elements in groups with similar chemical reactivity.  Today, we know that these groups have analogous outer electron configurations (valence electrons when s and p orbitals are being filled) but remarkably, electrons, protons and neutrons were not discovered until decades after Mendeleev developed his table.  In addition, because the importance of protons as the determiner of the element was not discovered until 1913 by Moseley, Mendeleev ordered the elements according to the best available measured parameter which at that time was atomic mass.  To his credit, he recognized that this resulted in incorrect alignment of a few of the elements such as I and Te but he prioritized reactivity over atomic mass and put them in their appropriate positions.   The typical periodic table now arranged according to increasing atomic number contains the elemental symbol, the atomic number and atomic mass.  From the position of the element in the chart, the atomic number and mass, it is possible to ascertain substantial information about each of the elements and to predict meaningful trends going across periods and down groups [4].

      Electrons are added to the lowest available energy level of an atom according to the Aufbau Principle and generally are added using the Madelung energy ordering rule.  Diagrams have been developed to illustrate the Aufbau Principle [5].  It is possible to deduce the ordering of the sublevels from the periodic table and vice versa to develop the periodic table using the Aufbau Principle.  In 1930,  a table that combined the concepts of the periodic table with the Aufbau Principle was published by Gardner and Mazzucchelli [6].  The concept was also used by Miguel Catalan [7] and developed further and promoted extensively by Edward Mazurs [8].  Pauling [9] and Halliday and Resnick [10] have also used this approach.  Mazurs has described the aufbau-periodic table as "the best representation of the periodic system."

For the Mazurs' tables [8] and others that combined the periodic table with the Aufbau Principle, most of the designers except for Pauling [9] followed the traditional periodic table approach of starting with hydrogen at the top.  To conform more to the Aufbau style, this project like Pauling's started with hydrogen at the bottom and built up from there with the energy of the sublevels increasing.  (This note was added on 2/9/21 with the finding that Jodogne also used an aufbau model with both build up and build down examples between the years of 1985 and 2020 [16].)  One of the original goals was to have the vertical axis represent the relative energy levels of the sublevels.  This challenge could not be met as the energy levels are extremely dependent on many variables including atomic number and especially the number of electrons in a sublevel.  As can be observed in the graph below [11], the first ionization energy of the elements has multifold variability.  For an example, in an Aufbau diagram, the energy levels of all of the 3 p electrons are placed at the same level but the ionization energies of these elements have almost a 3-fold range.  This illustrates that electron – electron interaction plays a major role in determining the energy level.   It should be noted that the placement of a line on a piece of paper does not fix the energy level and the level moves up or down significantly as electrons are added to the other p orbitals.  For the d and f orbitals, the range of values is less than for s and p electrons. (image from ref.[9])


In addition to the ionization energies, the significant number of exceptions to the Madelung rule demonstrates that the energy levels move as electrons are added [5f,12].  Examples include Cr, Cu, La, Ac and 16 additional elements.  Consequently, the attempt to use relative energy as the vertical axis was essentially abandoned although the full version does show that the energy levels get closer together as the energy increases and a small modification was made for the positions of La and Ac.  The condensed version, because of space issues, does not attempt to use relative energies on the vertical axis.  For example, the 1s and 2s orbitals are much closer together than they should be.  Placement of helium is a problem in periodic tables as helium is an inert gas and belongs in the inert gas group.  However, it can be argued that helium should be in the group with 2 valence electrons.  In the full chart above, helium was placed in the vertical column containing other inert gases.  Because of space, helium was placed next to hydrogen in the condensed version.


The use of color as a key or code in periodic tables for a property of the elements has been discussed [13]It is common to use color to distinguish the different electron sublevels (e.g., s, p, d, f).  Color has also been used recently using RGB codes and color descriptions from the Chemcool web site [14] to develop Mendeleev-like periodic tables with the color representing the color of the element in its elemental state [15]. A table of this type is included near the bottom of this document. Use of color in this way has also been included in the two Aufbau Periodic Tables that are included on the 2nd and 3rd pages of this document.  There are some issues with the use of color as some elements such as phosphorous and carbon have allotropes with different colors.  Also the color description of cesium of silvery-gold does not have an RGB code.  An attempt to find a code for silvery-gold was made but it should be recognized that this author has mild red-green color blindness and the color included for cerium might be incorrect.


     For more web sites on chemistry and other topics by this author, please visit: and the following for periodic table information: For an organic chemistry directory, please visit: .






















8.  a.   






    g.  Mazurs, E., Graphic Representations of the Periodic System During One Hundred Years, Univ. of Alabama, 1974
        For reviews, please visit:


  9.  Pauling, L., General Chemistry, Freeman, 1958, 2nd ed. p. 220.


11.  Graph made using Excel and values from:





16.  a.  Jon Claude Jodogne web/CN 133.pdf 

Periodic Table  Links

A.  Properties, Graphing and/or Ranking Capability
B.  Properties
C.  Interactive and/or Animated Periodic Table
D.  Images of Elements
E.  About the Periodic Table
F. Mendeleev and the History of the Periodic Table
  Emission Spectra of Elements and Electron Structure
H.  Isotopes
I.  Chemogenesis (chemical reactivity from the periodic table)
J.  Compilation of Elemental Properties and Abundances
K.  Elemental Toxicities
L.  Sources, Uses, Functions and Mineralogy of Elements
M.  Native Elements
N.  Periodic Table Videos
O.  Extended Periodic Table
P.  Vertical Periodic Table
Q.  Periodic Table Printmaking Projects 
R.  Periodic Table of Comic Books
S.  The Element Song by Tom Lehrer
T.  Periodic Table Templates
U.  Directories of Periodic Tables
V.  Origin of the names of the elements
W.  Prices of the elements

    A. Properties, Graphing and/or Ranking Capability

WebElements -
T. Gray -

    B. Properties
electron configurations - 
x-ray - 

    C. Interactive and/or Animated Periodic Tables

    D. Images of Elements

    E. About the Periodic Table

    F. Mendeleev and the History of the Periodic Table

   G. Emission Spectra of Elements and Electron Structure 

   H. Isotopes 

   I. Chemogenesis (chemical reactivity from the periodic table) 

  J. Compilation of Elemental Properties and Abundances,occur%20at%20less%20than%200.15%25.

   K. Elemental Toxicities 

   L. Sources, Uses, Functions and Mineralogy of Elements 

   M.  Native Elements 

    N. Periodic Table Videos

    O. Extended Periodic Table

    P. Vertical Periodic Table

    Q. Periodic Table Printmaking Projects  

    R. Periodic Table of Comic Books, emojis and Haiku, books, Disney characters

    S. The Element Song by Tom Lehrer

    T.  Periodic Table Templates

   U.  Directories of Periodic Tables

V.  Origin of the names of the elements
     Peter Wothers, How the Elements are Named: 
            Antimony, Gold, Jupiter's Wolf
, see:

.  Prices of the elements  periodic table with element prices’s-precious-metals


Some periodic table questions and unresolved issues.

1.  There are at least four commonly used versions of the periodic table:  the long, the medium-long, the left step and the pyramidal.  While some experts have preferences for one or another, each has strengths and weaknesses.  Which one do you prefer and why?

medium-long and long (not up-to-date with names) (medium long and long but not up-to-date with names)

long form

medium-long form

left step

pyramidal version (not up-to-date with names)

2.  The positions of some elements in periodic tables are still disputed. 

a.  Does hydrogen belong in the alkali metals group or the halogen group or neither?

b.  There are some claims that second period elements have properties inconsistent with the remaining members of their groups.  Explain this statement.

c.  Some medium-long periodic tables have lanthanum part of the “f” group of elements (split out from the periodic table), others have lutetium as a member of the 14 elements and still others include 15 elements in the “f” group .  What is the best placement of these two elements?  Part of the issue is the priority of chemical properties versus electronic structure.  If electronic structure is taken as the determining criteria, are there other elements that are misplaced in the periodic table?

d.  Does helium belong in Group 2 or Group 18?

3.  The IUPC numbers the groups from 1 through 18 but American periodic tables often have A and B group elements with the numbers running from 1A through 8A and 1B through 8B.  State the advantages and disadvantages of each and your preference (for a table with both, see tables above or

4.  Is the periodic table universal or could there be differences on another planet?  For example, consider the universality of atomic masses.

5.  Does the periodic table contain any isotope information?  Consider use of the atomic mass as a source of isotope information (See:  S. Murov, Chem 13 News, March, 2010.  “Promoting Insight:  Atomic Mass”.

6.  The periodic table above attempts to illustrate the approximate colors of the elements.  The orange staircase in the two periodic tables is commonly included in many periodic tables to very qualitatively separate the metals and the non-metals.  Do the colors of the elements also help to distinguish metals from non-metals and, if so, does this method correlate with the staircase model?  Which method do you think has more merit?  (Note:  It is often suggested that the elements adjacent to the staircase are metalloids, semiconductors and/or semimetals.  The consensus is that boron, silicon, germanium, arsenic, antimony and tellurium are metalloids with a few others in the questionable category.  For a discussion of criteria used to characterize metalloid properties, please see:

7.  Calculations indicate that stability of nuclei depend on the neutron to proton ratio and predict an island of stability above atomic number 110.  Is it possible that there are some "longer lived isotopes" with atomic number above 110?  (e.g., see:

8.  What is the probability that elements with atomic number greater than 118 will ever be synthesized?
    (e.g., see: )


9.  In some cases, discoveries have been made virtually simultaneously by different people in different countries (e.g., 1772, 1963).  Is this just a coincidence or are other factors in play here?  


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