Class 11 Chemistry · Chapter 3
Short answer:
Class 11 Chemistry Chapter 3 "Classification of Elements and Periodicity in Properties" periodic table ki poori logic samjhata hai — kyun elements ek particular order me arrange hain aur unke atomic radius, ionization enthalpy, electron gain enthalpy, aur electronegativity jaise properties ek predictable, periodic pattern follow karte hain. Ye rationalised 2026-27 syllabus ke 9 chapters me se Chapter 3 hai, Part I ka hissa.
Chapter 2 (Structure of Atom) ne tumhe electron configuration ki neev di thi — Chapter 3 usi neev par poori Chemistry ka sabse powerful predictive tool khada karta hai: Periodic Table. Ye sirf ek chart yaad karne wala chapter nahi hai; ye samjhata hai ki kyun Mendeleev ka atomic-mass wala system fail hua aur Moseley ka atomic-number wala Modern Periodic Law sahi nikla, kaise s-, p-, d-, f-block elements unki electronic configuration se directly nikalte hain, aur sabse important — atomic radius, ionization enthalpy, electron gain enthalpy aur electronegativity ke trends kis physical reasoning (effective nuclear charge, shielding, shell addition) se aate hain. Jo bhi is chapter ko sirf 'trend yaad karo' bana kar padhta hai, exam me exceptions (Be>B, N>O, Ga>Al) par phas jata hai — is spec me har trend ka kaaran diya gaya hai, na ki sirf direction. Ye chapter aage Chapter 4 (Chemical Bonding), Chapter 7 (Redox Reactions) aur poori Organic Chemistry (Chapter 8-9) ki foundation banta hai, isliye ise thoroughly clear karna zaroori hai.
Chapter 3 Summary — 5 Minute Revision
Modern Periodic Law kehta hai ki elements ke properties unke atomic number ka periodic function hain (Mendeleev ke atomic mass ke bajaye). Periodic table me period number = valence shell ka principal quantum number (n), aur elements ko unki electronic configuration ke basis par s-, p-, d-, f-blocks me classify kiya jata hai. Chaar major periodic trends — atomic/ionic radius, ionization enthalpy, electron gain enthalpy, aur electronegativity — sab effective nuclear charge, shielding effect, aur shell-addition ke combination se explain hote hain: period me left→right jaate hue radius ghatta hai jabki IE aur electronegativity badhti hain; group me top→bottom jaate hue radius badhta hai jabki IE aur electronegativity ghatti hain. Kuch important exceptions (Be>B, N>O in IE; Cl>F in EA; Ga>Al anomaly) chapter ka sabse exam-relevant hissa hain. Isoelectronic species (same electron count, different Z) ki radius comparison bhi frequently poocha jata hai.
In-Text Questions — Solutions
Diye gaye elements ko unke atomic number ke increasing order me arrange karke check karo ki kya unki properties periodic pattern follow karti hain (e.g., Li, Be, B, C, N, O, F, Ne).
Ye Period 2 ka poora set hai. Jaise-jaise atomic number badhta hai (Li→Ne), valence electrons ns¹ se ns²np⁶ tak fill hote jaate hain — isliye properties (atomic radius ghatna, IE badhna, metallic se nonmetallic character) ek clear periodic pattern follow karti hain, jo Modern Periodic Law ko confirm karta hai.
Ek element ki electronic configuration [Ne]3s²3p¹ di gayi hai — iska period aur group batao.
Highest principal quantum number n=3 hai → Period 3. Valence configuration ns²np¹ hai (1 electron p-subshell me) → Group 13. Ye element Aluminium (Al) hai.
Na⁺, Mg²⁺, aur Ne — inme se kaun-kaun isoelectronic hain aur inki radius ka comparative order kya hoga?
Teeno species me 10-10 electrons hain (Ne configuration), isliye ye isoelectronic hain. Nuclear charge badhne ke saath (Ne=10 < Na⁺=11 < Mg²⁺=12) usi electron-cloud par pull badhta hai, isliye radius order: Mg²⁺ < Na⁺ < Ne.
Hydrogen atom ke electron ki ground-state energy −2.18×10⁻¹⁸ J hai. Iski ionization enthalpy kJ/mol me nikaalo.
ΔᵢH = 0 − (−2.18×10⁻¹⁸ J) = 2.18×10⁻¹⁸ J/atom
Per mole = 2.18×10⁻¹⁸ × 6.022×10²³ ≈ 1312 kJ/mol
Yehi H ki experimentally observed IE (~1312 kJ/mol) se match karta hai.
Al³⁺ aur Cl⁻ ke binary compound ka formula predict karo unki valency ke basis par.
Al ki valency +3 aur Cl ki valency −1 hai. Charges ko balance karne ke liye 3 Cl⁻ ki zaroorat hai:
Al³⁺ + 3Cl⁻ → AlCl₃
O²⁻ aur F⁻ me se konsa bada hoga, aur kyun?
Dono isoelectronic hain (10 electrons), lekin O ka nuclear charge (Z=8) F (Z=9) se kam hai. Kam nuclear charge ka matlab electron cloud par kam pull, isliye O²⁻ (radius ~1.40 Å) > F⁻ (radius ~1.36 Å) hota hai.
Poore Class 11 Chemistry ke handwritten colour notes
IITian & district toppers ke banaye short notes — revision-ready, diagram ke saath. Board se pehle poora syllabus 3 din me revise.
Exercise Questions — Solutions (Q1–Q40)
3.1 Periodic table me organisation ka basic theme kya hai?
Periodic table me elements ko unke increasing atomic number ke order me arrange kiya jata hai. Har element ki position uski electronic configuration reflect karti hai — jin elements ka valence-shell electronic configuration similar hota hai unhe same group me rakha jata hai, isliye unke chemical properties bhi similar hote hain. Yahi Modern Periodic Law ka core idea hai: elements ke physical aur chemical properties, unke atomic number ka periodic function hote hain.
3.2 Mendeleev ne apni periodic table classify karne ke liye kaunsi important property use ki, aur kya woh usi scheme par strictly tike rahe?
Mendeleev ne atomic mass (atomic weight) use kiya — elements ko increasing atomic mass ke order me arrange kiya. Lekin woh strictly is scheme par tike nahi rahe: kuch pairs (jaise Co–Ni, Te–I, Ar–K) me unhone chemical properties ko priority di aur atomic mass order ko invert kar diya, taaki similar properties wale elements same group me aa sakein.
3.3 Mendeleev ke Periodic Law aur Modern Periodic Law ke approach me basic difference kya hai?
Mendeleev's Law: properties, atomic mass ka periodic function hain. Modern Periodic Law (Moseley, based on atomic number): properties, atomic number (proton count) ka periodic function hain. Atomic number wala criterion sahi hai kyunki isse Co–Ni, Te–I jaise anomalous pairs automatically sahi order me aa jaate hain, jinhe atomic mass basis par explain nahi kiya ja sakta tha.
3.4 Quantum numbers ke basis par justify karo ki sixth period me 32 elements hone chahiye.
Sixth period me n=6 tak filling hoti hai aur Aufbau order ke hisaab se filling hoti hai: 6s, 4f, 5d, 6p.
Max electrons = 6s² (2) + 4f¹⁴ (14) + 5d¹⁰ (10) + 6p⁶ (6) = 32
Isliye sixth period me total 32 elements hote hain.
3.5 Z = 114 wala element period aur group me kahan locate karoge?
Z = 114 ki electronic configuration [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p² tak jaati hai. 7p subshell fill ho rahi hai isliye ye Period 7 me hai, aur outer configuration ns²np² hone se ye Group 14 (p-block, carbon family) me aata hai — ye element Flerovium (Fl) hai.
3.6 Third period aur seventeenth group me present element ka atomic number likho.
Period 3, Group 17 wala element Chlorine (Cl) hai, jiska atomic number = 17 hai.
3.7 Tumhare hisaab se konsa element (i) Lawrence Berkeley Laboratory ne aur (ii) Seaborg's Group ne naam diya hoga?
(i) Berkelium (Bk, Z = 97) — Lawrence Berkeley National Laboratory ke naam par naamit.
(ii) Seaborgium (Sg, Z = 106) — Glenn T. Seaborg (jinke research group ne heavy elements discover kiye) ke sammaan me naamit.
3.8 Same group ke elements ke physical aur chemical properties similar kyun hote hain?
Same group ke elements ka valence-shell electronic configuration same hota hai (sirf principal quantum number n badalta hai). Chemical behaviour mainly valence electrons decide karte hain, isliye same group ke elements ke bonding pattern aur reactivity broadly similar hoti hai, chahe unka atomic number alag ho.
3.9 Atomic radius aur ionic radius ka actual matlab kya hai?
Atomic radius = nucleus ke center se outermost shell tak ki distance (jo bonding ke type ke hisaab se covalent, metallic, ya van der Waals radius ho sakta hai). Ionic radius = ionic crystal lattice me ek cation aur anion ke beech ki effective distance, jise unke sizes ke hisaab se apportion kiya jata hai.
3.10 Ek period aur ek group me atomic radius kaise vary karta hai?
Period me (left→right): Atomic radius decreases — nuclear charge badhta hai jabki electrons wahi shell me add hote hain, to effective nuclear charge badhne se electrons nucleus ke paas kheenche jaate hain.
Group me (top→bottom): Atomic radius increases — naya shell (n badhta hai) add hota hai, jo increased nuclear charge ke effect ko overpower kar deta hai.
3.11 Isoelectronic species ka concept samjhao aur diye gaye species ke isoelectronic species naam do: (i) F⁻ (ii) Ar (iii) Mg²⁺ (iv) Rb⁺
Isoelectronic species woh atoms/ions hote hain jinke electrons ki total sankhya same ho.
- (i) F⁻ (10 e⁻) → isoelectronic: Ne, Na⁺, Mg²⁺, O²⁻, N³⁻
- (ii) Ar (18 e⁻) → isoelectronic: Cl⁻, K⁺, Ca²⁺, S²⁻
- (iii) Mg²⁺ (10 e⁻) → isoelectronic: Ne, Na⁺, F⁻, O²⁻
- (iv) Rb⁺ (36 e⁻) → isoelectronic: Kr, Sr²⁺, Br⁻
3.12 Species N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺, Al³⁺ consider karo. (a) In sab me common kya hai? (b) Inhe increasing ionic radius ke order me arrange karo.
(a) Sab species isoelectronic hain — har ek me 10 electrons hain (Ne jaisi configuration).
(b) Jitna zyada nuclear charge (Z), utna hi strong pull us fixed electron cloud par, isliye radius chhota. Increasing order:
Al³⁺ < Mg²⁺ < Na⁺ < F⁻ < O²⁻ < N³⁻
3.13 Explain karo ki cations apne parent atom se chhote aur anions bade kyun hote hain.
Cation: electron(s) hatane se effective nuclear charge per electron badh jata hai, aur kabhi-kabhi poora outer shell hi hat jata hai — isliye cation chhota hota hai.
Anion: electron(s) add hone se electron-electron repulsion badhti hai aur effective nuclear charge per electron ghat jata hai, jisse electron cloud phailta hai — isliye anion bada hota hai.
3.14 Ionization enthalpy aur electron gain enthalpy ki definition me 'isolated gaseous atom' aur 'ground state' ka significance kya hai?
Isolated gaseous atom: ensure karta hai ki koi bhi interatomic ya intermolecular interaction (bonding, solvation) measurement ko affect na kare — property sirf atom ki apni hai.
Ground state: ensure karta hai ki atom lowest energy state me ho, taaki measured energy change ek fixed, standard reference se ho, na ki kisi excited state se — isse values comparable rehti hain.
3.15 Atomic hydrogen ki ionization enthalpy calculate karo, agar iske electron ki energy E = −2.18 × 10⁻¹⁸ J hai.
Ionization enthalpy = electron ko infinity tak (E=0) le jaane ke liye chahiye energy:
ΔᵢH = E(∞) − E(ground) = 0 − (−2.18 × 10⁻¹⁸ J) = 2.18 × 10⁻¹⁸ J/atom
Per mole (× Nₐ = 6.022 × 10²³):
ΔᵢH = 2.18 × 10⁻¹⁸ × 6.022 × 10²³ = 1.312 × 10⁶ J/mol ≈ 1312 kJ/mol
3.16 Period 2 ke elements ke liye ionization enthalpy ka order explain karo.
General trend: nuclear charge badhne se IE₁ left se right badhti hai — Li < B < Be < C < O < N < F < Ne. Do exceptions hain:
- Be > B: Be ka 2s² configuration fully-filled aur stable hai, B ka 2p¹ electron nikalna aasan hai.
- N > O: N ka 2p³ configuration half-filled aur extra-stable hai, O me ek electron-pair repulsion IE ko thoda kam kar deti hai.
3.17 Sodium aur magnesium ki first aur second ionization enthalpies compare karo.
IE₁: Na (496 kJ/mol) < Mg (738 kJ/mol) — Mg ka nuclear charge zyada hai aur uska 3s² configuration stable filled hai.
IE₂: Na (4562 kJ/mol) >> Mg (1450 kJ/mol) — Na⁺ already stable Ne-jaisi configuration me hai isliye dusra electron nikalna extremely mushkil; Mg⁺ ka doosra electron nikalne se Mg²⁺ ko bhi stable Ne configuration milti hai, isliye IE₂(Mg) moderate hai.
3.18 Ek group me neeche jaate hue ionization enthalpy kam hone ke factors kya hain?
Group me neeche jaate hue: (i) atomic radius badhta hai (naya shell add), (ii) inner electrons ka shielding effect badhta hai — in dono ki wajah se valence electron par effective nuclear charge ka pull kam ho jata hai, jo nuclear charge ke absolute increase ko overpower kar deta hai. Nateeja: electron nikalna aasan ho jata hai, IE ghat jati hai.
3.19 Group 13 me ionization enthalpies ki deviations explain karo.
Expected trend B > Al > Ga > In > Tl (regular decrease) hona chahiye, par actual me IE₁(Ga) > IE₁(Al) hota hai. Wajah: Ga ki configuration [Ar]3d¹⁰4s²4p¹ hai — filled 3d electrons poorly shield karte hain (d-block/poor shielding effect), isliye Ga ka effective nuclear charge expected se zyada hota hai, jo IE ko thoda badha deta hai.
3.20 (i) O ya F, (ii) F ya Cl — inme se kiska electron gain enthalpy zyada negative hai?
(i) F ka EA (−328 kJ/mol) O (−141 kJ/mol) se zyada negative hai — F chhota hai aur uska effective nuclear charge zyada hai, electron add hona zyada favourable hai.
(ii) Cl ka EA (−349 kJ/mol) F (−328 kJ/mol) se zyada negative hai — F ka size itna chhota hai ki uske compact 2p orbital me naya electron aane par electron-electron repulsion zyada hoti hai, jo EA ko thoda kam negative bana deti hai; Cl ka 3p orbital bada hone se ye repulsion kam hoti hai.
3.21 Kya oxygen ki second electron gain enthalpy positive, more negative, ya less negative hogi first ke comparison me? Kyun?
O ki second electron gain enthalpy (O⁻ + e⁻ → O²⁻) positive hogi. Wajah: O⁻ pehle se hi negatively charged hai, isliye ek aur electron add karne me electron aur anion ke beech electrostatic repulsion ko overcome karne ke liye energy supply karni padti hai — ye process endothermic hota hai.
3.22 Electron gain enthalpy aur electronegativity me basic difference kya hai?
Electron gain enthalpy: isolated gaseous atom (ground state) ke electron gain karne par hone wala energy change — ek measurable thermodynamic quantity hai (units me).
Electronegativity: ek bonded atom ki, covalent bond ke shared electron pair ko apni taraf kheenchne ki relative tendency — ye ek numerical scale (jaise Pauling scale) hai, koi fixed physical unit nahi.
3.23 'Nitrogen har compound me same electronegativity dikhata hai' — is statement par apna reaction do.
Ye statement galat hai. Electronegativity koi absolute fixed atomic property nahi hai — ye us atom ke hybridization state, oxidation state, aur bonding environment par depend karti hai. Isliye nitrogen alag-alag compounds me (sp, sp², sp³ hybridization ke hisaab se) thodi alag electronegativity dikha sakta hai.
3.24 Theory describe karo ki jab ek atom (a) electron gain karta hai aur (b) electron lose karta hai, tab atomic radius kaise badalta hai.
(a) Electron gain: electron-electron repulsion badhti hai, effective nuclear charge per electron kam hota hai → electron cloud phailta hai → radius badhta hai (anion bada hota hai).
(b) Electron loss: repulsion kam hoti hai, effective nuclear charge per electron badhta hai, kabhi-kabhi shell hi khatam ho jata hai → radius ghatta hai (cation chhota hota hai).
3.25 Kya ek element ke isotopes ki first ionization enthalpies same hongi ya different? Kyun?
Practically same hongi. Ionization enthalpy mainly electronic configuration (jo proton number/atomic number par depend karti hai) se decide hoti hai, na ki neutron count (mass number) se. Isotopes ka electronic structure identical hota hai, isliye unki IE₁ same maani jaati hai.
3.26 Metals aur nonmetals ke beech major differences kya hain?
| Property | Metals | Nonmetals |
|---|---|---|
| Electron behaviour | Electrons lose karke cation banate hain | Electrons gain karke anion banate hain |
| Ionization enthalpy | Low | High |
| Electron gain enthalpy | Less negative | Zyada negative |
| Nature | Electropositive | Electronegative |
| Physical | Malleable, ductile, conductor | Brittle, poor conductor (mostly) |
| Oxide nature | Basic | Acidic |
↔ Table ko side me swipe karein
3.27 Periodic table use karke: (a) outer subshell me 5 electrons wale element ka group batao (b) 2 electrons lose karne wale element ka group (c) 2 electrons gain karne wale element ka group (d) ek aisa group jisme metal, nonmetal, liquid aur gas sab present ho.
(a) Outer configuration ns²np³ (5 valence electrons) → Group 15 (e.g., N, P).
(b) 2 electrons easily lose karta hai (ns²) → Group 2 (alkaline earth metals, e.g., Mg, Ca).
(c) 2 electrons gain karta hai (ns²np⁴) → Group 16 (e.g., O, S).
(d) Group 17 (halogens) — F aur Cl room temperature par gas hain, Br liquid hai, I solid nonmetal hai aur At metalloid/weak-metallic character dikhata hai — ek hi group me teeno physical states aur metallic-to-nonmetallic spectrum mil jata hai.
3.28 Reactivity order explain karo: Group 1 me Li < Na < K < Rb < Cs, aur Group 17 me F > Cl > Br > I.
Group 1 (alkali metals): reactivity depend karti hai electron lose karne ki ease par. Neeche jaate hue atomic size badhta hai, IE ghatti hai, isliye electron lose karna aasan hota hai → reactivity Li se Cs tak badhti hai.
Group 17 (halogens): reactivity depend karti hai electron gain karne ki ease par. Neeche jaate hue size badhta hai, incoming electron par nuclear pull kam hota hai, bond dissociation aur hydration enthalpy bhi favorable nahi rehti — isliye reactivity F se I tak ghatti hai.
3.29 s-, p-, d-, f-block elements ke general outer electronic configuration likho.
| Block | General configuration |
|---|---|
| s-block | ns¹⁻² |
| p-block | ns²np¹⁻⁶ |
| d-block | (n−1)d¹⁻¹⁰ ns⁰⁻² |
| f-block | (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns² |
↔ Table ko side me swipe karein
3.30 Diye gaye electronic configurations se element ki position (period, group) assign karo.
Method: sabse bada principal quantum number (n) jisme electron hai woh period number deta hai; valence-shell electron count (aur block ka pattern) group number deta hai.
Example: configuration 1s²2s²2p⁶3s² wale element me highest n = 3 aur valence config ns² hai → Period 3, Group 2. Isi tarah 1s²2s²2p⁶3s²3p³ wale element ke liye highest n=3, valence ns²np³ → Period 3, Group 15. Har diye gaye configuration par yahi do-step method apply karo.
3.31 Diye gaye ionization enthalpy aur electron gain enthalpy data ka use karke identify karo: (a) least reactive element (b) most reactive metal (c) most reactive nonmetal (d) least reactive nonmetal (e) MX₂ (ionic) halide banane wala metal (f) MX (covalent) halide banane wala metal.
Ye answer diye gaye specific IE/EA data-table par depend karta hai, par general method ye hai:
- (a) Least reactive element = jiska IE sabse zyada aur EA near-zero ho (usually noble gas — stable octet).
- (b) Most reactive metal = jiska IE₁ sabse kam ho (electron loss sabse aasan).
- (c) Most reactive nonmetal = jiska EA sabse zyada negative ho (electron gain sabse favourable).
- (d) Least reactive nonmetal = jiska EA sabse kam negative ho (noble gas ko chhod kar).
- (e) MX₂ (ionic halide) banane wala metal = usually Group 2 metal (valency 2, large electropositive character, e.g. Mg → MgCl₂).
- (f) MX (covalent halide) banane wala metal = high polarizing power wala small/high-charge-density metal (e.g. Be → BeCl₂).
3.32 Following elements ke pairs se banne wale binary compounds ke formula predict karo: (a) Lithium aur oxygen (b) Magnesium aur nitrogen (c) Aluminium aur iodine (d) Silicon aur oxygen (e) Phosphorus aur fluorine (f) Element 71 aur fluorine.
| Pair | Valencies | Formula |
|---|---|---|
| (a) Li + O | 1, 2 | Li₂O |
| (b) Mg + N | 2, 3 | Mg₃N₂ |
| (c) Al + I | 3, 1 | AlI₃ |
| (d) Si + O | 4, 2 | SiO₂ |
| (e) P + F | 3 (or 5), 1 | PF₃ (ya PF₅) |
| (f) Z=71 (Lu) + F | 3, 1 | LuF₃ |
↔ Table ko side me swipe karein
3.33 Modern periodic table me, period number kis quantum number ki value indicate karta hai?
Period number, us element ke valence shell ke principal quantum number (n) ki value ko indicate karta hai — jaise Period 3 ke elements me valence electrons n=3 shell me hote hain.
3.34 Modern periodic table ke regarding incorrect statement identify karke correct karo: 'Atomic radius period me left se right jaate hue badhta hai.'
Ye statement incorrect hai. Sahi fact: period me left se right jaate hue atomic radius badhta nahi, ghatta hai — kyunki nuclear charge badhta hai jabki electrons usi shell me add hote hain, isliye effective nuclear charge badhne se atomic size chhota hota jata hai.
3.35 In factors me se kaunsa factor valence shell ko affect NAHI karta: nuclear charge, shielding effect, mass number, principal quantum number?
Mass number valence shell ko affect nahi karta. Valence shell ka size aur energy nuclear charge (proton count), shielding/screening effect, aur principal quantum number par depend karte hain — mass number (jo neutron count se judta hai) electronic configuration ko change nahi karta.
3.36 Ionization enthalpy ke regarding incorrect statement identify karo: 'IE period me left se right hamesha bina exception ke regularly badhti hai.'
Ye statement incorrect hai. IE ka general trend period me left→right increasing hota hai, lekin isme exceptions hain — jaise Be>B (stable filled 2s²) aur N>O (stable half-filled 2p³) — isliye trend 'bina exception' nahi hai.
3.37 Elements Na, Mg, Al, Si ko unke atomic radius ke increasing order me arrange karo.
Period 3 me left se right jaate hue atomic radius ghatta hai (Na sabse bada, Si sabse chhota), isliye increasing order:
Si < Al < Mg < Na
3.38 B, Al, Mg, K ko unke metallic character ke correct increasing order me arrange karo.
Metallic character group me neeche jaane par badhta hai aur period me left→right ghatta hai. B (metalloid boundary, least metallic) se K (alkali metal, most metallic) tak:
B < Al < Mg < K
3.39 B, C, N, F, Si ko unke non-metallic character ke correct increasing order me arrange karo.
Non-metallic character period me left→right badhta hai aur group me upar jaane par badhta hai. Si (Period 3, kam electronegative) sabse kam nonmetallic hai; Period 2 series me B<C<N<F badhte hain. Increasing order:
Si < B < C < N < F
3.40 F, Cl, O, N ko unke oxidizing property ke correct order me arrange karo.
Oxidizing power electronegativity/electron-accepting tendency se related hai. Standard accepted order:
F > O > Cl > N
F sabse strong oxidizer hai (highest electronegativity), N sabse kamzor (comparatively low electronegativity, stable N≡N bond ban jata hai jo N₂ ko less reactive banata hai).
Important Equations — Ek Nazar Me
| Concept | Rule / Formula |
|---|---|
| Modern Periodic Law | Properties element ke atomic number ka periodic function hain (Mendeleev ke atomic mass ke bajaye) |
| Period number | = valence shell ka principal quantum number (n) |
| s-block config | ns¹⁻² |
| p-block config | ns²np¹⁻⁶ |
| d-block config | (n−1)d¹⁻¹⁰ ns⁰⁻² |
| f-block config | (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns² |
| Atomic radius trend (period) | Left → Right: decreases (eff. nuclear charge ↑) |
| Atomic radius trend (group) | Top → Bottom: increases (shells ↑) |
| Isoelectronic species | Same electron count → jitna nuclear charge (Z) zyada, radius utna chhota |
| Ionization enthalpy (IE) | ΔᵢH = E(∞) − E(ground state); IE₁ < IE₂ < IE₃ ... (successive IE hamesha badhti hai) |
| IE trend (period / group) | Left→Right: increases (exceptions Be>B, N>O); Top→Bottom: decreases |
| Electron gain enthalpy (EA) | Isolated gaseous ground-state atom + e⁻ → anion + energy change; most negative near halogens (Cl sabse negative, F nahi) |
| Electronegativity (Pauling scale) | Bonded atom ki shared electron pair kheenchne ki relative tendency; period me L→R badhti, group me top→bottom ghatti |
| Cation vs Anion size | Cation < parent atom < Anion |
| Valency (typical group pattern) | Group 1→4: valency = group number; Group 5→17: valency = 8 − group number |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Atomic radius period me left se right 'badhta hai' likh dena — actually ghatta hai kyunki effective nuclear charge badhta hai.
- Ionization enthalpy ka trend 'bina exception' regular maan lena — Be>B aur N>O jaise anomalies bhool jaana jo stable (filled/half-filled) configurations ki wajah se hote hain.
- Electron gain enthalpy sabse negative Fluorine ki maan lena — actually Chlorine ka EA F se zyada negative hai (F ka chhota size electron-electron repulsion badhata hai).
- Electron gain enthalpy aur electronegativity ko same quantity samajh lena — dono alag concepts hain (isolated atom ka thermodynamic quantity vs bonded atom ki relative tendency).
- Isoelectronic species ki radius sabki 'same' maan lena — electron count same hone par bhi nuclear charge alag hone se radius alag hoti hai.
- Second/third ionization enthalpy ko first se kam ya same expect karna — successive IE hamesha badhti hai, khaaskar jab stable noble-gas configuration touch ho jaaye toh jump bahut bada hota hai.
Board-Style Important Questions
- Modern Periodic Law ko state karo.
- Na aur Mg ki first ionization enthalpy compare karo aur kaaran do.
- Isoelectronic species ki concept samjhao aur N³⁻, O²⁻, F⁻ ko increasing ionic radius ke order me arrange karo.
- Group 13 me ionization enthalpy ki deviation (Ga vs Al) explain karo.
- Periodic table me atomic radius, ionization enthalpy, electron gain enthalpy, aur electronegativity ke period tatha group trends ko kaaran sahit describe karo.
- Cations chhote aur anions parent atom se bade kyun hote hain, samjhao.
Aksar Poochhe Jaane Wale Sawaal
Class 11 Chemistry Chapter 3 'Classification of Elements and Periodicity in Properties' ke NCERT solutions PDF kahan milenge?
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Class 11 Chemistry ka current 2026-27 rationalised syllabus me kitne chapters hain?
Rationalised 2026-27 session me Class 11 Chemistry syllabus me sirf 9 chapters hain (pehle 14 the). Class 11 chemistry all chapters list ncert ke hisaab se: 1) Some Basic Concepts of Chemistry, 2) Structure of Atom, 3) Classification of Elements and Periodicity in Properties, 4) Chemical Bonding and Molecular Structure, 5) Thermodynamics, 6) Equilibrium, 7) Redox Reactions, 8) Organic Chemistry: Some Basic Principles and Techniques, 9) Hydrocarbons.
Class 11 chemistry deleted syllabus topics kaunse hain, aur kya periodicity chapter unme se hai?
Nahi — Classification of Elements and Periodicity chapter poori tarah syllabus me hai. Jo poore chapters/units rationalise karke hataye gaye hain woh hain: States of Matter (Gases and Liquids), Hydrogen, s-Block Elements, Some p-Block Elements, aur Environmental Chemistry.
Chapter 2 (Structure of Atom) aur Chapter 3 (Periodicity) ka connection kya hai?
Bahut deep connection hai — periodicity poori tarah electronic configuration par based hai jo chapter 2 me padha jata hai. Agar chapter 2 structure of atom important questions clear nahi hain (quantum numbers, orbital filling, Aufbau principle), toh periodic trends samajhna mushkil hoga, kyunki har trend (radius, IE, EA) directly electron configuration se explain hota hai.
Classification of elements and periodicity in properties ke important questions kaunse topics se aate hain?
Sabse zyada important: atomic/ionic radius trends, ionization enthalpy ke exceptions (Be>B, N>O), electron gain enthalpy anomaly (Cl>F), isoelectronic species aur unki radius comparison, aur s/p/d/f-block ki general electronic configuration. Ye topics har saal exam me repeat hote hain.
Periodicity chapter ke baad next konsa chapter padhna chahiye, aur usme kya naya hai?
Sequence ke hisaab se agla Chapter 4 — Chemical Bonding and Molecular Structure hai, jiske notes pdf me tum yahi periodic trends (electronegativity, ionization enthalpy) apply karke bond nature predict karna seekhte ho. Uske baad Chapter 5 Thermodynamics numericals aur Chapter 6 Equilibrium ncert solutions aate hain, jinke liye bhi ye chapter ki electronic-structure foundation kaam aati hai.
Class 11 Chemistry — Saare Chapters
Board exam tak sirf revision karna hai?
Class 11 Chemistry ke saare chapters ke colour handwritten short notes — diagrams, formulas aur important points ek jagah.
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