Elements 89-102 are called actinides. Electrons added during the Aufbau construction of actinide atoms go into the 5f subshell.
Actinides are unstable and undergo radioactive decay .
The most common actinides on Earth are uranium and thorium. Hydrogen is not considered an alkali metal, despite its position on some periodic tables. An oxide of an alkaline earth metal , which produces an alkaline solution in reaction with water. A substance that can act as either an acid or a base in a reaction. Compare with ionic radius .