Period 7 element

While the first five of these synthetic elements (americium through einsteinium) are now available in macroscopic quantities, most are extremely rare, having only been prepared in microgram amounts or less.

Whilst francium and radium do show typical properties of their respective groups, actinides display a much greater variety of behavior and oxidation states than the lanthanides.

These peculiarities are due to a variety of factors, including a large degree of spin–orbit coupling and relativistic effects, ultimately caused by the very high electric charge of their massive nuclei.

[note 2] Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays.

[9] Radium (Ra, atomic number 88) is an almost pure-white alkaline earth metal, but it readily oxidizes, reacting with nitrogen (rather than oxygen) on exposure to air, becoming black in color.

In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite.

Radium is not necessary for living things, and adverse health effects are likely when it is incorporated into biochemical processes due to its radioactivity and chemical reactivity.

The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

[11][15] Nuclear tests have released at least six actinides heavier than plutonium into the environment; analysis of debris from a 1952 hydrogen bomb explosion showed the presence of americium, curium, berkelium, californium, einsteinium and fermium.

The further distinction of having an atomic number greater than the actinides is significant in several ways: Transactinides are radioactive and have only been obtained synthetically in laboratories.

IUPAC defines an element to exist if its lifetime is longer than 10−14 second, the time needed to form an electron cloud.