Glenn T. Seaborg who, in
1945, suggested a new
periodic table showing
the actinides as belonging
to a second f-block series
Theodor Benfey's spiral periodic table
periodic table layout, also known as the common or standard form (as shown at various other points in this article), is
attributable to Horace Groves Deming. In 1923, Deming, an American chemist, published short (Mendeleev style (http://www.meta-
synthesis.com/webbook/35_pt/pt_database.php?PT_id=456)) and medium (18-column (http://www.meta-
synthesis.com/webbook/35_pt/pt_database.php?PT_id=360)) form periodic tables.
Merck and Company prepared a handout form
of Deming's 18-column medium table, in 1928, which was widely circulated in American schools. By the 1930s Deming's table was
appearing in handbooks and encyclopaedias of chemistry. It was also distributed for many years by the Sargent-Welch Scientific
With the development of modern quantum mechanical theories of electron
configurations within atoms, it became apparent that each period (row) in the table
corresponded to the filling of a quantum shell of electrons. Larger atoms have more
electron sub-shells, so later tables have required progressively longer periods.
In 1945, Glenn Seaborg, an American scientist, made
the suggestion that the actinide elements, like the
lanthanides were filling an f sub-level. Before this time
the actinides were thought to be forming a fourth d-
block row. Seaborg's colleagues advised him not to
publish such a radical suggestion as it would most likely
ruin his career. As Seaborg considered he did not then
have a career to bring into disrepute, he published
anyway. Seaborg's suggestion was found to be correct
and he subsequently went on to win the 1951 Nobel
prize in chemistry for his work in synthesizing actinide
Although minute quantities of some transuranic elements occur naturally,
they were all first discovered in
laboratories. Their production has expanded the periodic table significantly, the first of these being
neptunium, synthesized in 1939.
Because many of the transuranic elements are highly unstable and
decay quickly, they are challenging to detect and characterize when produced. There have been
controversies concerning the acceptance of competing discovery claims for some elements, requiring independent review to determine
which party has priority, and hence naming rights. The most recently accepted and named elements are flerovium (element 114) and
livermorium (element 116), both named on 31 May 2012.
In 2010, a joint Russia–US collaboration at Dubna, Moscow Oblast,
Russia, claimed to have synthesized six atoms of ununseptium (element 117), making it the most recently claimed discovery.