The actinoids (or actinides) are a series of ranging from atomic numbers 89 to 103. Named after their first member, actinium , these elements form the lower row of the f-block. Atomic Range: Actinium ( ) to Lawrencium (
Unlike their "sister" series (the lanthanoids), actinoids show a much wider range of oxidation states, making their chemistry highly complex. actinoid
Every single element in this series is radioactive . Natural vs. Synthetic: Only thorium ( ) and uranium ( The actinoids (or actinides) are a series of
) occur in significant quantities in nature; most others are man-made (synthetic). ✨ Key Properties Every single element in this series is radioactive
Their chemical behavior is defined by electrons progressively filling the 5f orbital.
As the atomic number increases, the atomic and ionic radii steadily decrease due to poor shielding by 5f electrons.