Inner Transition Elements — f-Block Elements

1. Lanthanides (4f series):

• Elements from Lanthanum (La, Z=57) to Lutetium (Lu, Z=71) — 14 elements
• General electron configuration: [Xe] 4f¹⁻¹⁴ 5d⁰⁻¹ 6s²
• Also called Rare Earth Elements (though not actually rare)
• All are silvery-white metals with similar properties (making them difficult to separate)
• Used in: colour TV tubes, lasers, magnets (Nd-Fe-B magnets — strongest permanent magnets)

2. Actinides (5f series):

• Elements from Actinium (Ac, Z=89) to Lawrencium (Lr, Z=103) — 14 elements
• General electron configuration: [Rn] 5f¹⁻¹⁴ 6d⁰⁻¹ 7s²
• All actinides are radioactive (unlike most lanthanides)
• Most actinides beyond Uranium (Z=92) are synthetic (man-made) elements
• Used in: nuclear reactors (Uranium, Thorium), nuclear weapons (Plutonium)

If lanthanides and actinides were placed in the main body of the periodic table, it would become too wide (32 columns wide) to fit on a standard page. So they are traditionally extracted and shown at the bottom. Their position in the table is actually after Group 2 (alkaline earth metals).