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The INTERNET Database of Periodic Tables

There are thousands of periodic tables in web space, but this is the only comprehensive database of periodic tables & periodic system formulations. If you know of an interesting periodic table that is missing, please contact the database curator: Mark R. Leach Ph.D.

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2019

Group 3 of The Periodic Table

There are several ways in which the 'common/modern medium form' periodic table are shown with respect to the Group 3 elements and how the f-block is shown. Indeed, there is even some dispute about which elements constitute Group 3. There are three general approaches to showing Group 3:

(See Scerri's take and Thyssen's view on this matter.)

So, which one of the three options is 'better'?

The general feeling amongst the knowledgeable is that leaving a gap is not an option, so it comes down to:

Sc, Y, La, Ac     vs.     Sc, Y, Lu, Lr

René Vernon has looked as the properties of the potential Group 3 elements, including: densities, 1st ionisation energies, ionic radii, 3rd ionisation energies, melting points & electron affinity:

Figure 1 shows that a Z plot of the density values for Sc, Y, La, Lu Ac and Lr follows a smooth trendline.

Figure 2 shows that a Z plot of the first ionization energy values follows a smooth trendline.

Figure 3 shows that a Z plot of the 6-coordinate ionic radii for the subject elements bifurcates after Y into an -La-Ac tranche (R2 = 0.99) and a -Lu-Lr branch (0.61). The trendline for -La-Ac is smoother.

Figure 4 shows a Z plot of 3rd ionisation energy values bifurcating after Y into a -Lu-Lr tranche (R2 = 0.83) and a -La-Ac branch (0.98). The trendline for -La-Ac is smoother.

Figure 5 shows that a Z plot of the melting points bifurcates after Y into an -Lu-Lr (R2 = 0.72) tranche and a -La-Ac (0.71) branch. While the fit values for the two options are comparable, -Lu-Lr is preferred since Y and La show a greater departure from trend.

Figure 6 has a Z plot of electron affinity values bifurcating after Y into an -La-Ac tranche (R2 = 0.85) and a -Lu-Lr branch (0.99).[iii] The trendline supports Lu-Lr. The trend-lines by themselves are inconclusive: two show no difference; two support -La-Ac; two support -Lu-Lr.

Upon reviewing the data, René's comment is that: "The net result is that the two options seem inseparable" and he proposes that IUPAC adopt the following periodic table numbering system:

Professor Sir Martyn Poliakoff's [of the Periodic Videos YouTube channel & Nottiningham University] take on this matter:

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© Mark R. Leach Ph.D. 1999 –


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