Electromagnetic spectrum recap — UV, visible, IR, NMR, microwave, X-ray

4.8.1 · Chemistry › Spectroscopy & Analysis (Intro)

WHY do we care?

Spectroscopy woh tarika hai jisse chemists microscope ke bina molecules ko dekhte hain. EM spectrum ka har region sirf itni hi energy rakhta hai ki matter ke andar ek specific event excite ho sake:

Region	Energy	Kya excite karta hai
X-ray	sabse zyada	core (inner-shell) electrons ko bahar nikaalta hai
UV–Visible	zyada	valence electron transitions (π→π, n→π)
Infrared (IR)	medium	bond vibrations (stretch, bend)
Microwave	kam	molecular rotations
Radio (NMR)	sabse kam	magnetic field mein nuclear spin flips

Teen master equations (derived, dumped nahi)

$c = λ ν$ kyun? Speed = distance ÷ time. Ek second mein, $ν$ crests guzarte hain, aur har crest $λ$ metres door hai, toh wave front $λ \times ν$ metres per second travel karta hai.

$c = λ ν$

Energy kaise enter hoti hai (Planck/Einstein): Light packets (photons) mein aati hai. Experiment (photoelectric effect) ne dikhaya ki har packet ki energy frequency ke proportional hoti hai, proportionality constant $h$ ke saath (Planck's constant, $6.626 \times 1 0^{- 34} J s$ ):

$E = h ν$

Dono ko combine karo — $ν = c / λ$ substitute karo:

$E = h ν = \frac{h c}{λ}$

Figure — Electromagnetic spectrum recap — UV, visible, IR, NMR, microwave, X-ray

Approximate landmarks (inhe memorise karo!)

Worked examples

Steel-man your mistakes

Active recall

Recall Khud ko test karne ke liye click karo

Q: Kaunse region mein sabse zyada energy ke photons hote hain? → X-ray.
Q: IR kaunsi molecular event probe karta hai? → Bond vibrations.
Q: $E$ ko $λ$ ke terms mein likho. → $E = h c / λ$ .
Q: NMR radio waves kyun use karta hai? → Nuclear spin flips ke liye bahut kam energy chahiye.
Q: Wavenumber ke units aur definition? → cm⁻¹, $\overset{ν}{ˉ} = 1/ λ$ .

Recall Feynman: ek 12-saal ke bachche ko samjhao

Socho ek line mein dost khade hain — kuch bilkul paas-paas (short wave) aur kuch bahut door-door (long wave). Jo paas-paas hain woh ek energetic, tezi se buzz karne wali line jaisi hain — yeh X-ray/UV light hai, itni strong ki cheezein (electrons) gira de. Jo door-door, aaram se hain woh radio waves hain — itni gentle ki woh bas ek atom ke andar ek tiny compass needle (nucleus) ko thoda hilaa sakti hain. Hum molecule pe alag-alag tarah ki light daalte hain aur dekhte hain kaunsi woh "khaata" hai. Jo bhi khaata hai woh batata hai uska kaunsa hissa hila — koi spinning part, koi hilta hua spring, ya koi jumping electron. Aise hum molecule kya bana hai yeh pata lagate hain bina use chue.

Flashcards

c, λ, ν ke beech relationship

c = λ ν

(speed = wavelength × frequency)

Frequency ke terms mein ek photon ki energy

E = h ν

h = 6.626 \times 1 0^{- 34}

J·s

Wavelength ke terms mein ek photon ki energy

E = h c / λ

Kya energy wavelength ke proportional hai ya inversely proportional?

Inversely:

E \propto 1/ λ

Increasing energy ke order mein EM regions ka order

Radio(NMR) < Microwave < IR < Visible < UV < X-ray

UV–Visible dwara probe ki gayi molecular event

Valence electron transitions (π→π*, n→π*)

IR dwara probe ki gayi molecular event

Bond vibrations (stretching, bending)

Microwave dwara probe ki gayi molecular event

Molecular rotations

NMR dwara probe ki gayi molecular event

Magnetic field mein nuclear spin flips

X-ray dwara probe ki gayi molecular event

Inner-shell (core) electron transitions / diffraction

Wavenumber ki definition

\overset{ν}{ˉ} = 1/ λ

, units cm⁻¹;

E \propto \overset{ν}{ˉ}

Visible light ka wavelength range

~400 nm (violet) se ~700 nm (red) tak

E=hc/λ mein λ metres mein kyun honi chahiye

h (J·s) aur c (m/s) ke saath SI units consistent rakhne ke liye

Wavenumber ko frequency mein convert karo

ν = c \overset{ν}{ˉ}

Connections

UV-Visible Spectroscopy — π→π* aur n→π* transitions, Beer–Lambert law
IR Spectroscopy — functional-group fingerprint region, $\overset{ν}{ˉ}$ cm⁻¹ mein
NMR Spectroscopy — chemical shift, $B_{0}$ mein spin states
Planck's Quantum Theory — $E = h ν$ ka origin
Photoelectric Effect — photon energy ka experimental basis
Atomic Structure — Electron Transitions — energy levels aur absorption
Beer-Lambert Law — quantitative absorbance