General Introduction — Revision Notes

⚡ 30-Second Revision

d-Block (Transition Elements): — Groups 3-12. Filling of $(n-1)d$ orbitals.
General E.C. (d-block): — $(n-1)d^{1-10}ns^{1-2}$.
Exceptions: — Cr ($[Ar]3d^54s^1$), Cu ($[Ar]3d^{10}4s^1$) due to $d^5$/$d^{10}$ stability.
True Transition Elements: — Incompletely filled d-orbitals in ground state or common O.S.
Non-Transition d-block: — Zn, Cd, Hg (always $d^{10}$ in common O.S.).
f-Block (Inner Transition Elements): — Two series below main table. Filling of $(n-2)f$ orbitals.
General E.C. (f-block): — $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$.
Lanthanoids (4f series): — Ce (Z=58) to Lu (Z=71). E.C.: $[Xe]4f^{1-14}5d^{0-1}6s^2$.
Actinoids (5f series): — Th (Z=90) to Lr (Z=103). E.C.: $[Rn]5f^{1-14}6d^{0-1}7s^2$. All are radioactive.

2-Minute Revision

The d-block elements, or transition elements, occupy the central part of the periodic table (Groups 3-12). Their defining characteristic is the progressive filling of the $(n-1)d$ orbitals, leading to a general electronic configuration of $(n-1)d^{1-10}ns^{1-2}$.

Key exceptions like Chromium ($[Ar]3d^54s^1$) and Copper ($[Ar]3d^{10}4s^1$) are crucial, arising from the enhanced stability of half-filled ($d^5$) or completely filled ($d^{10}$) d-orbitals. It's vital to remember that not all d-block elements are true transition elements; Zinc, Cadmium, and Mercury are excluded because their d-orbitals are completely filled ($d^{10}$) in both their ground state and common oxidation states.

The f-block elements, known as inner transition elements, are placed separately at the bottom. They are characterized by the filling of the $(n-2)f$ orbitals. This block comprises two series: lanthanoids (4f series, Ce-Lu) with a general configuration of $[Xe]4f^{1-14}5d^{0-1}6s^2$, and actinoids (5f series, Th-Lr) with $[Rn]5f^{1-14}6d^{0-1}7s^2$.

All actinoids are radioactive. This introductory knowledge forms the bedrock for understanding their detailed chemical properties.

5-Minute Revision

A thorough understanding of the general introduction to d and f block elements is paramount for NEET. The d-block elements, spanning Groups 3-12, are often called transition elements due to their bridging position and the filling of $(n-1)d$ orbitals.

Their general electronic configuration is $(n-1)d^{1-10}ns^{1-2}$. Remember the critical exceptions: Chromium (Cr, Z=24) is $[Ar]3d^54s^1$ (not $3d^44s^2$) and Copper (Cu, Z=29) is $[Ar]3d^{10}4s^1$ (not $3d^94s^2$).

These anomalies are due to the extra stability of half-filled ($d^5$) and fully-filled ($d^{10}$) subshells. A key conceptual point is the definition of a 'transition element': it must have incompletely filled d-orbitals in its ground state or any common oxidation state.

This excludes Zinc (Zn, Z=30), Cadmium (Cd, Z=48), and Mercury (Hg, Z=80) because their d-orbitals are always $d^{10}$ in their stable forms. For example, $Zn^{2+}$ is $[Ar]3d^{10}$.

The f-block elements, or inner transition elements, are characterized by the filling of the $(n-2)f$ orbitals and are placed separately. Their general electronic configuration is $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$. They are divided into two series:

1
Lanthanoids (4f series): — From Cerium (Ce, Z=58) to Lutetium (Lu, Z=71). Their configuration is typically $[Xe]4f^{1-14}5d^{0-1}6s^2$. They are known for their similar chemical properties.
2
Actinoids (5f series): — From Thorium (Th, Z=90) to Lawrencium (Lr, Z=103). Their configuration is $[Rn]5f^{1-14}6d^{0-1}7s^2$. All actinoids are radioactive, and they exhibit more variable oxidation states than lanthanoids.

Worked Example: Identify the block and series for an element with Z=60. Solution: Z=60 is Neodymium (Nd). The noble gas before it is Xenon (Xe, Z=54). After Xe, electrons fill $6s^2$ (Ba, Z=56), then $5d^1$ (La, Z=57), and then the $4f$ orbitals start filling. For Z=60, the configuration is $[Xe]4f^46s^2$. Since the $4f$ orbital is being filled, it's an f-block element, specifically a lanthanoid (4f series). This systematic approach helps in correctly classifying elements.

Prelims Revision Notes

General Introduction to d and f Block Elements (NEET Revision)

I. d-Block Elements (Transition Elements)

Position: — Groups 3 to 12 in the periodic table.
Defining Feature: — Progressive filling of the $(n-1)d$ orbitals.
General Electronic Configuration: — $(n-1)d^{1-10}ns^{1-2}$.
Key Exceptions (for stability):

* Chromium (Cr, Z=24): $[Ar]3d^54s^1$ (expected $3d^44s^2$) – for half-filled $d^5$. * Copper (Cu, Z=29): $[Ar]3d^{10}4s^1$ (expected $3d^94s^2$) – for fully-filled $d^{10}$. * Similar exceptions exist in 4d and 5d series (e.g., Mo, Ag, Au).

Definition of Transition Element: — An element having incompletely filled d-orbitals in its ground state or in any one of its common oxidation states.
Non-Transition d-Block Elements: — Zinc (Zn, Z=30), Cadmium (Cd, Z=48), Mercury (Hg, Z=80).

* Reason: They have completely filled d-orbitals ($d^{10}$) in both their ground state and common oxidation states (e.g., $Zn^{2+}$ is $[Ar]3d^{10}$). Hence, they do not exhibit typical transition metal properties.

II. f-Block Elements (Inner Transition Elements)

Position: — Placed separately below the main body of the periodic table.
Defining Feature: — Progressive filling of the $(n-2)f$ orbitals.
General Electronic Configuration: — $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$.
Two Series:

1. Lanthanoids (4f Series): * Elements from Cerium (Ce, Z=58) to Lutetium (Lu, Z=71). * General E.C.: $[Xe]4f^{1-14}5d^{0-1}6s^2$. * Characterized by similar chemical properties due to poor shielding of 4f electrons. 2. Actinoids (5f Series): * Elements from Thorium (Th, Z=90) to Lawrencium (Lr, Z=103). * General E.C.: $[Rn]5f^{1-14}6d^{0-1}7s^2$. * All are radioactive. Exhibit more variable oxidation states than lanthanoids.

III. Key Differences (d-block vs. f-block):

Orbital Filling: — $(n-1)d$ vs. $(n-2)f$.
Position: — Middle vs. Bottom.
Oxidation States: — More variable for d-block vs. less variable for lanthanoids (mostly +3).
Radioactivity: — Generally non-radioactive d-block vs. all actinoids radioactive.

IV. Important Points for NEET:

Memorize the specific atomic numbers where f-block series begin (Ce Z=58, Th Z=90).
Understand the 'why' behind exceptions and definitions, not just rote memorization.

Vyyuha Quick Recall

To remember the d-block elements that are NOT true transition elements: "Zinc Can't Have Gold" (Zn, Cd, Hg). This reminds you that these elements, despite being in the d-block, do not meet the criteria for transition elements due to their filled d-orbitals.