General electronic configuration (n−1)d¹⁻¹⁰ ns⁰⁻²

3.3.1 · Chemistry › d-Block (Transition Metals) & f-Block

Symbol ka MATLAB kya hai?

$(n - 1)$ kyun aur $n$ kyun nahi? Kyunki $d$ -orbitals sabse pehle $ℓ = 2$ ke saath available hote hain, jiske liye $n_{orbital} \geq 3$ zaroori hai. Jab tak aap period $n$ par pahunchte ho, woh $d$ -subshell ek number neeche wali shell ka hissa ban chuka hota hai. Jaise Period 4 ( $n = 4$ ) $3 d$ orbitals fill karta hai — exactly $n - 1 = 3$ .

$s$ , $d$ se pehle kyun fill hota hai? (First principles se derivation)

Hum order ko kabhi sirf "memorise" nahi karte. Hum ise energy se derive karte hain.

Period-4 elements ke liye $4 s$ aur $3 d$ compare karo:

Orbital	$n$	$ℓ$	$n + ℓ$
$4 s$	4	0	4
$3 d$	3	2	5

Kyunki $4 s$ ka $(n + ℓ)$ chhota hai, yeh pehle fill hota hai. Isliye hum build karte waqt $\dots 4 s^{2} 3 d^{x}$ likhte hain, bhale hi fill hone ke baad convention ke hisaab se $3 d$ ko $4 s$ se pehle list karte hain.

Figure — General electronic configuration (n−1)d¹⁻¹⁰ ns⁰⁻²

Famous exceptions: Cr aur Cu

Kaun se elements actually count karte hain?

Common Mistakes (Steel-man + Fix)

Worked example 3: Manganese ion configurations

Recall Feynman: 12 saal ke bachche ko samjhao

Ek parking garage imagine karo. Ground floor ( $s$ ) mein daakhil hona aasaan hai, isliye gaadiyaan pehle wahan park karti hain — lekin ek number neeche thodi khaas " $d$ " jagahein hain jo ek baar garage bhar jaane par aur bhi aaram-deh ho jaati hain. Toh gaadiyaan pehle ground floor par aati hain, lekin jaate waqt ground-floor wali gaadiyaan (bahar hone ki wajah se, pakadna aasaan) pehle jaati hain. Transition metals woh atoms hain jinki chhipi $d$ floor partly bhari hai — aur yahi half-empty floor unhe colourful, magnetic, aur reactions fast karne wala banati hai.

Active Recall

General d-block valence configuration

(n - 1) d^{1 - 10} n s^{0 - 2}

(n - 1) d

kyun hai aur

n d

kyun nahi?

d

-orbitals ko

ℓ = 2

chahiye (orbital

n \geq 3

); period

n

mein woh

d

ek neeche wali shell ka hissa hota hai,

n - 1

Fill order dene wala rule, aur uska physical basis

(n + ℓ)

(Madelung) rule; chhota

n + ℓ

= zyada penetration/kam shielding = chhoti energy; ties chhote

n

se toot te hain.

4 s

3 d

ke liye

n + ℓ

4 s

4

;

3 d

5

→

4 s

pehle fill hota hai.

Cr (Z=24) ka ground-state config aur kyun

[Ar] 3 d^{5} 4 s^{1}

; half-filled

3 d^{5}

exchange+symmetry stability gain karta hai.

Cu (Z=29) ka ground-state config aur kyun

[Ar] 3 d^{10} 4 s^{1}

; fully-filled

3 d^{10}

extra stable hota hai.

Ionisation par electron removal ka order

n s

pehle remove hota hai

(n - 1) d

se (jab

d

fill hone ke baad neeche sink karta hai

n s

se).

Fe, Fe²⁺, Fe³⁺ configs

[Ar] 3 d^{6} 4 s^{2}

;

[Ar] 3 d^{6}

;

[Ar] 3 d^{5}

Transition element ki IUPAC definition

Atom YA stable ion mein partially filled

d

-subshell ho.

Zn/Cd/Hg typical transition metals kyun nahi hain

Ye atom aur common

+ 2

ion dono mein

d^{10}

hain → koi partially filled

d

nahi.

Connections

Aufbau Principle and Madelung Rule
Exchange Energy and Hund's Rule
Variable Oxidation States of Transition Metals
Colour and d-d Transitions
Magnetic Properties (spin-only formula)
f-Block (n-2)f orbitals filling
Effective Nuclear Charge and Shielding