Variation of oxidation state across the table

2.2.9 · Chemistry › Periodic Trends

1. Oxidation state kya hota hai? (WHAT)

Key bookkeeping rules (inhi se har number neeche derive hota hai):

Free element $= 0$ (jaise $O_{2}$ , $Na$ ).
Neutral molecule mein oxidation states ka sum $= 0$ ; ion mein $=$ uska charge.
Common "anchors": $O = - 2$ , $H = + 1$ (zyada EN partner ke saath), Group 1 $= + 1$ , Group 2 $= + 2$ , F $= - 1$ hamesha.

2. Maximum positive oxidation state derive karna (HOW)

Main-group elements ke liye first-principles derivation:

Group number (purana 1–8 style / naya 1,2,13–18) batata hai valence electron count $n_{v}$ .
Unhe saare ke saare zyada-EN partners (usually O ya F) ko de do.
Maximum positive state $= + n_{v}$ .

$Max positive OS = + n_{v} = (group valence electrons)$

Check: group 17 ke liye (Cl, $n_{v} = 7$ ) max hota hai $+ 7$ , jo $HClO_{4}$ mein dikhai deta hai jahaan $+ 1 + x + 4 (- 2) = 0 \Rightarrow x = + 7. ✓$

3. Minimum (most negative) oxidation state derive karna

$Min OS = - (8 - n_{v})$

Nitrogen ke liye ( $n_{v} = 5$ ): min $= - (8 - 5) = - 3$ , jo $NH_{3}$ mein milta hai. Max $= + 5$ , jo $HNO_{3}$ mein milta hai.

Figure — Variation of oxidation state across the table

4. Ek period ACROSS trends

Metals (left): sirf positive states, group number ke barabar (Na $+ 1$ , Mg $+ 2$ , Al $+ 3$ ). WHY: low ionisation energy — $e^{-}$ khoye aasaani se, gain karna mushkil.
Non-metals (right): dono dikhaate hain — ek high positive (O/F ke saath) aur ek negative state.
Middle (p-block): sabse zyada variety, kyunki yeh valence $p$ + $s$ electrons khona bhi kar sakte hain ya kuch gain bhi.

5. Ek group DOWN trends — "inert pair effect"

Yahi wajah hai ki $PbCl_{2}$ stable hai lekin $PbCl_{4}$ ek decomposing oxidiser hai.

6. Transition metals — variable oxidation states

Manganese iska poster child hai: $+ 2$ (Mn²⁺), $+ 3$ , $+ 4$ ( $MnO_{2}$ ), $+ 6$ ( $MnO_{4}^{2 -}$ ), $+ 7$ ( $MnO_{4}^{-}$ ). Max $= + 7 = 3 d^{5} 4 s^{2}$ electron count.

7. Worked examples

Recall Feynman: ek 12-saal ke bache ko samjhao

Socho har atom ek baccha hai jiske pocket mein kuch marbles (electrons) hain. Ek "bully" atom (bahut electronegative, jaise oxygen) marbles cheen leta hai; ek "generous" atom (ek metal) unhe de deta hai. Oxidation state bas yahi hai — kitne marbles tune diye (plus) ya liye (minus). Table ke left mein rehte hain generous bacche jo kuch marbles dete hain (+1, +2). Right mein rehte hain grabbers. Daayein jaate hue, bachon ke paas dene ke liye zyada marbles hote hain aur woh ek full pocket ke paas bhi hote hain, isliye dono kar sakte hain. Transition-metal bacchon ke paas marbles do alag-alag paas waali pockets mein hote hain, isliye woh ek-ek karke de sakte hain — yahi wajah hai ki unke itne saare numbers hote hain!

Active-recall flashcards

Oxidation state kya hota hai?

Kisi atom par wo hypothetical charge jo hota agar har bond fully ionic treat kiya jaaye, shared electrons ko zyada electronegative atom ko deke.

Main-group element ka maximum positive oxidation state ka formula?

+ n_{v}

, jo uske valence electrons ki sankhya ke barabar hai (group valence).

Non-metal ka most negative oxidation state ka formula?

- (8 - n_{v})

Transition metals kyun 1 se different itne saare oxidation states dikhate hain?

Kyunki

3 d

aur

4 s

orbitals energy mein paas hote hain, isliye electrons dono se ek-ek karke remove ho sakte hain.

Inert-pair effect kya hai?

Group mein neeche jaate hue

n s^{2}

pair bonding karne mein reluctant ho jaata hai, isliye lower oxidation state (group max − 2) zyada stable ho jaati hai, jaise Pb

+ 4

ke bajaye

+ 2

prefer karta hai.

H_{2} SO_{4}

mein S ka oxidation state aur kyun?

+ 6

;

2 (+ 1) + x + 4 (- 2) = 0

se, jo S ke 6 valence electrons se match karta hai.

Oxygen usually positive kyun nahi hoti?

O se zyada electronegative almost kuch bhi nahi hai (sirf F), isliye koi isko electrons donate nahi karta.

Mn ka max oxidation state aur uska electron basis?

+ 7

, jo uske

3 d^{5} 4 s^{2} = 7

removable electrons ke barabar hai.

Period 3 mein max positive OS kaisa change karta hai?

Har step par

+ 1

se badhta hai, Na (

+ 1

) se Cl (

+ 7

) tak.

Connections

Electronegativity — decide karta hai ki shared electrons "kise milte hain".
Ionisation Energy — set karta hai ki positive states kitni aasaani se bante hain.
Electron Affinity — set karta hai ki negative states kitni jaldi bante hain.
Electronic Configuration — $n_{v}$ aur $d$ – $s$ spacing yahaan se aata hai.
Inert Pair Effect — heavy p-block behaviour control karta hai.
Transition Metal Chemistry — variable states redox aur colour drive karte hain.
Redox Reactions — application: oxidation-number change se balancing.