1.4.3
Definition Period, Group, Block
Ek period ek horizontal row hai (kul 7 periods hain). Period number = ground state mein occupied sabse bada principal quantum number n .
Ek group ek vertical column hai (kul 18 groups hain). Ek group ke elements ka same outer (valence) electron arrangement hota hai → similar chemistry.
Ek block (s, p, d, f) ka naam us orbital ke type ke naam pe rakha jaata hai jisme last-added electron jaata hai.
Intuition WHY blocks exist karte hainElectrons orbitals mein increasing energy ke order mein fill hote hain (Aufbau). Har orbital type ek fixed number of electrons rakh sakta hai, aur woh number exactly us block ki width hoti hai.
Ek given type ke orbitals ki sankhya (magnetic quantum number m l = − l ⋯ + l
orbitals = 2 l + 1 , max electrons = 2 ( 2 l + 1 )
Factor 2 kyun? Har orbital 2 electrons rakhta hai (spin up + spin down, m s = ± 2 1
Worked example WHY period 1 mein sirf 2 elements hainPeriod 1 sirf n = 1 n = 1 l = 0 l = 0 … n − 1 1s orbital exist karta hai → max 2 electrons → H aur He .
Yeh step kyun? n = 1 p l
Worked example WHY period 2 mein 8 elements hainPeriod 2 mein n = 2 l = 0 l = 1 = 2 + 6 = 8 Yeh step kyun? 2 p
Intuition WHY d-block pehli baar 4th period mein appear karta haiEnergy ordering (n + l n + l n 1 s < 2 s < 2 p < 3 s < 3 p < n + l = 4 4 s < n + l = 5 3 d < 4 p … 4s (n+l=4) pehle fill hota hai 3d (n+l=5) se , 3 d pehli d-block row period 4 mein rehti hai , aur isliye f-block pehli baar period 6 mein appear karta hai (4f late fill hota hai).
Worked example Group number ↔ valence electrons
Group 1 (Li, Na, K…): outer n s 1 Group 17 (F, Cl, Br…): outer n s 2 n p 5 Group 18 (Ne, Ar…): outer n s 2 n p 6 Yeh kyun matter karta hai: same column = same valence count = chemistry ki same "shape". Yahi table ka pura payoff hai.
Recall Quick group→valence rule for main groupsGroups 1–2 ke liye: valence = = − 10
Common mistake "d-block period 3 mein hai kyunki 3d ke naam mein 3 hai."Kyun sahi lagta hai: orbital ko 3 d label kiya gaya hai, aur periods bhi number hote hain, toh lagta hai ki 3d elements period 3 ke hain.
Fix: Period number = occupied highest n s . Sc ke liye, outer shell 4 s 4 , chahe filling electron 3 d
Common mistake "Helium Beryllium ke upar jaata hai kyunki uski config1 s 2 s 2 Kyun sahi lagta hai: 1 s 2 s 2 Fix: Grouping chemical behaviour se hoti hai, aur He ka complete shell hai → woh noble gases ki tarah chemically inert hai. Toh woh Ne ke upar group 18 mein baithta hai. Configuration akela mislead kar sakta hai; filled-shell status jeet jaata hai.
Common mistake "Har period ki same length hoti hai."Kyun sahi lagta hai: yeh ek neat grid ke roop mein draw hota hai.
Fix: Lengths hain 2, 8, 8, 18, 18, 32, 32 — set hoti hain kin naye subshells ke available hone se . Naye p d f n
Mnemonic Fill-order chant & block widths"Silly People Don't Fumble" → s(2) p(6) d(10) f(14) widths.
Fill order by diagonals: "1s 2s 2p 3s 3p 4s 3d 4p…" — n l S odium P arty D ances F ine → s | (d beech mein) | p, with f neeche pull out.
Recall Feynman: ek 12-saal ke bacche ko explain karoEk stadium imagine karo jisme seats ke rings hain. Sabse andar ki choti ring (row 1) mein sirf 2 seats hain. Use fill karo, phir agla ring khulta hai zyada seats ke saath (8), aur baad mein bade rings mein aur bhi zyada (18, 32). Ek period = stadium ki ek ring. Ek group = seats ka ek column jo tum ring se ring tak seedha trace kar sakte ho — "same seat position" pe baithne waale log same tarah behave karte hain (jaise sab aisle wale log ek jaisa cheer karte hain). Blocks (s/p/d/f) sirf seating ke alag sections hain: chota VIP section (s, 2 seats), ek medium section (p, 6), ek bada (d, 10), ek bahut bada (f, 14). Naye sections sirf bade outer rings mein khulte hain — isliye neeche ki rows itni lambi hain!
Modern periodic table mein kitne groups aur periods hain? 18 groups (columns), 7 periods (rows).
Period number ek atom ke baare mein kya batata hai? Uske ground state mein occupied sabse bada principal quantum number n
s-block 2 columns wide kyun hai? Ek s orbital (l = 0 2 l + 1 = 1 2 × 1
d-block 10 columns wide kyun hai? Paanch d orbitals (l = 2 2 l + 1 = 5 2 × 5 = 10
Quantum number l 2 ( 2 l + 1 )
Pehli d-block row period 4 mein kyun appear hoti hai, period 3 mein nahi? Kyunki 4s (n + l = 4 n + l = 5
Group 17 (halogens) ki outer configuration? n s 2 n p 5
Helium group 18 mein kyun baithta hai, group 2 mein nahi? Uska complete outer shell hai (inert, noble-gas behaviour); grouping chemistry ke follow karta hai, na sirf s 2
d-block elements ki general valence configuration? ( n − 1 ) d 1 − 10 n s 0 − 2
Periods ki lengths 2, 8, 8, 18, 18, 32, 32 hain — iska kya cause hai? Naye subshell types (p, phir d, phir f) n
last-added electron names
d-block starts in period 4
