What is the primary criterion for classifying an element as a d-block element?

An element is classified as a d-block element primarily based on its electronic configuration. Specifically, it's an element in which the differentiating electron (the last electron added) enters one of the five d-orbitals of the penultimate shell, which is the $(n-1)d$ subshell. This means that these elements are characterized by the progressive filling of their d-orbitals as you move across a period in the d-block. This unique electron placement is responsible for many of their characteristic properties.

Why are f-block elements called 'inner transition elements'?

F-block elements are termed 'inner transition elements' because the differentiating electron enters the f-orbital of the anti-penultimate shell, which is the $(n-2)f$ subshell. This means the f-orbitals being filled are two shells inward from the outermost valence shell. In contrast, d-block elements fill d-orbitals in the penultimate shell ($(n-1)d$). The term 'inner' highlights this deeper orbital filling, distinguishing them from the 'outer' transition (d-block) elements.

Are all d-block elements considered transition elements? Explain.

No, not all d-block elements are considered true transition elements. The strict definition of a transition element requires it to have incompletely filled d-orbitals in its ground state or in any of its common oxidation states. Elements like Zinc (Zn), Cadmium (Cd), and Mercury (Hg) are d-block elements because their d-orbitals are being filled, but they have completely filled d-orbitals ($d^{10}$) in both their elemental state and their stable ionic forms. Hence, they do not exhibit typical transition metal properties like variable oxidation states or d-d electronic transitions.

What are the two series of f-block elements, and which orbitals are being filled in each?

The f-block elements are divided into two distinct series: the lanthanoids and the actinoids. The lanthanoids, also known as the 4f series, involve the progressive filling of the $4f$ orbitals. They follow Lanthanum (La) in the periodic table. The actinoids, or the 5f series, involve the progressive filling of the $5f$ orbitals. They follow Actinium (Ac) in the periodic table. Both series are placed separately at the bottom of the periodic table.

Why do d-block elements show variable oxidation states, while s-block elements typically do not?

D-block elements exhibit variable oxidation states due to the very small energy difference between the $(n-1)d$ orbitals and the $ns$ orbitals. This allows electrons from both these subshells to participate in bond formation. S-block elements, on the other hand, have a significant energy gap between their valence s-electrons and the next available orbitals, meaning only their outermost s-electrons are typically involved in bonding, leading to fixed oxidation states (e.g., +1 for Group 1, +2 for Group 2).

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Version 1Updated 22 Mar 2026

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The d-block elements, often referred to as transition elements, are those elements in the periodic table where the last electron enters one of the five d-orbitals of the penultimate shell, i.e., the $(n-1)d$ subshell. They occupy groups 3 to 12. The f-block elements, known as inner transition elements, are characterized by the filling of the $(n-2)f$ subshell. These elements are positioned separat…

Quick Summary

The d-block elements, also known as transition elements, occupy Groups 3 to 12 in the periodic table. They are characterized by the progressive filling of the $(n-1)d$ orbitals. Their general electronic configuration is $(n-1)d^{1-10}ns^{1-2}$ , with notable exceptions like Chromium and Copper due to the stability of half-filled or fully-filled d-orbitals.

A key distinction is that not all d-block elements are true transition elements; Zinc, Cadmium, and Mercury are d-block but not transition elements because they possess completely filled d-orbitals in their common oxidation states.

The f-block elements, or inner transition elements, are located separately at the bottom of the periodic table. They consist of two series: lanthanoids (4f series) and actinoids (5f series), where the $(n-2)f$ orbitals are being filled.

Their general electronic configuration is $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$ . This introductory understanding of their position and electronic configuration is fundamental to studying their unique chemical properties.

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Key Concepts

Electronic Configuration of d-Block Elements and Exceptions

The general electronic configuration for d-block elements is $(n-1)d^{1-10}ns^{1-2}$ . This means that…

Definition of Transition Elements vs. d-Block Elements

While all transition elements are d-block elements, not all d-block elements are considered transition…

General Electronic Configuration of f-Block Elements

The f-block elements, comprising lanthanoids and actinoids, have a general electronic configuration of…

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.

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.

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