Due to unpaired d-electrons and d–d transitions Variable oxidation states Can lose different numbers of d and s electrons Paramagnetism Caused by presence of unpaired electrons Catalytic activity Many act as catalysts (e.g., Fe in Haber process, V$_2$O$_5$ in contact process)

Special Note: Zn, Cd, Hg

Their configuration: $(n-1)d^{10} ns^2$
These are not considered typical transition elements because: They do not show variable oxidation states

Why Called Transition Elements?

Because they form a "transition"
Between highly reactive s-block metals and p-block elements
They gradually change metallic properties across the block.

The f-Block Elements

Key Characteristics

Feature	Details
All are metals	Both lanthanoids and actinoids are metallic in nature.
Inner Transition Elements	So called because their f-orbitals are being filled, and they're "inside" the transition series.
Similar properties in series	Lanthanoids show very similar chemical behavior; actinoids too to some extent.
Variable oxidation states	Especially in actinoids, where multiple oxidation states are possible.
Radioactivity	All actinoids are radioactive.
Synthetic elements	Many actinoids (especially after uranium) are man-made and exist only in trace amounts.
Transuranium Elements	Elements with atomic number $> 92$ (Uranium) are called transuranium elements.
Location in Periodic Table	Placed separately at the bottom of the periodic table. Includes two series: Lanthanoids: Cerium (Ce, $Z=58$) to Lutetium (Lu, $Z=71$) Actinoids: Thorium (Th, $Z=90$) to Lawrencium (Lr, $Z=103$)
Electronic Configuration	General configuration: $(n-2)f^{1-14} (n-1)d^{0-1} ns^2$ The last electron enters an f-orbital, which defines these as f-block elements.

What is Metallic Character?

Metallic character is the tendency of an atom to:

Lose electrons easily (to form positive ions, i.e., cations),
Show properties like malleability, ductility, lustre, high electrical & thermal conductivity.
The change from metallic to non-metallic character is not abrupt.

Direction	Metallic Character	Reason
$\downarrow$ Down a Group	Increases	Atomic size increases $\rightarrow$ easier to lose elect