SERIES PERIODIC TABLE CHEMISTRY SERIES

A simpler method yet is to order by atomic number and place the lanthanides and actinides within the Periodic Table reverting to the 32-element row form where Lu and Lr become Group 3 elements, an approach that finds support from atomic radius, ionisation energy, melting point, and electronegativity data trends. An alternative approach is to organise by electronic configuration, but every now and again certain elements buck the trend. The reasons for this seem to be historical, but there is an argument for this from the perspective of some of their chemical properties. This is because in many representations of the Periodic Table the 3rd and 4th Group 3 elements are not assigned, counter to the expedient premise in the introduction that this matter is settled, which brings us to one of the most contentious questions about the Periodic Table that is currently being addressed by an IUPAC Task Group: which elements are in Group 3-La and Ac or Lu and Lr?Īlthough many representations of the Periodic Table do not assign the 3rd and 4th Group 3 elements explicitly, some versions overtly place La and Ac in Group 3. This is understandable since a 32-element row representation generates presentational challenges, but the result is the incongruent occurrence of 15-element rows with electronic shells that can only hold 14 electrons. Seaborg moved the lanthanides and actinides out of the main Periodic Table to float below.

SERIES PERIODIC TABLE CHEMISTRY SERIES

However, it was not until the middle of the 20th century after the Manhattan Project-that enabled nuclear weapons and civil nuclear power-and the work of Seaborg making transuranic elements that the 5f actinide series was widely recognised, giving the Periodic Table we recognise today.

Bohr realised that the 4th primary atomic quantum shell can accommodate 32 electrons, leading to the recognition of the 4f lanthanide series. Moseley gave meaning to the concept of atomic number and thus the notion of fourteen elements between La and Hf. Indeed, in an era where many elements were discovered it took time to realise that some minerals thought to contain only one lanthanide element were actually several co-crystallised due to their similar radii, resulting in the famous, heroic example of James recrystallising a Tm salt 15 000 times to establish purity. Mendeleev gave us the basis of the Periodic Table 150 years ago, but at that time no one knew about f-orbitals. However, exactly where these elements end up is still not a settled matter. One thing most people can agree on is that the lanthanides and actinides belong somewhere towards the bottom of the Periodic Table. Since 2019 is designated as International Year of the Periodic Table, it is an appropriate time to reflect on lanthanide and actinide chemistry. The lanthanides and actinides, including Group 3 metals due to their chemical similarities, account for around a third of the Periodic Table, and they are key to a wide range of basic science research and societally beneficial technologies.

Series periodic table chemistry