The actinide group, also known as the actinide series or actinoids

 The actinide group, also known as the actinide series or actinoids, comprises 15 radioactive elements from actinium (Ac) to lawrencium (Lr) in the periodic table, characterized by filling the 5f subshell. 

Here's a more detailed look:

Definition:

The actinide series consists of the 15 elements following actinium (atomic number 89) and ending with lawrencium (atomic number 103). 

Location:

These elements are typically placed below the main body of the periodic table to maintain its structure. 

Key Characteristics:

Radioactivity: All actinides are radioactive, meaning their isotopes are unstable and decay over time. 

Metallic Nature: They are all metallic elements. 

Synthetic Elements: Many actinides are synthetic, meaning they are not found naturally on Earth and are produced in laboratories. 

Similar Properties: They share similar chemical and physical properties, often forming cations (positively charged ions). 

Examples of Actinides:

Actinium (Ac) 

Thorium (Th) 

Protactinium (Pa) 

Uranium (U) 

Neptunium (Np) 

Plutonium (Pu) 

Americium (Am) 

Curium (Cm) 

Berkelium (Bk) 

Californium (Cf) 

Einsteinium (Es) 

Fermium (Fm) 

Mendelevium (Md) 

Nobelium (No) 

Lawrencium (Lr)