SUB-ATOMIC PARTICLES Atomic Spectra of Hydrogen • When electron changes its orbit, energy

Structure of Atom change occurs in quanta.

Electron (e- ) Proton (p) Neutron (n) Radiations emitted by hydrogen in discharge tube
DEVELOPMENTS LEADING TO THE BOHR’S MODEL OF hc
Position Moves around Constituent Constituent experiment when passed through prism gives six ∆E = E - E = h ν or =
ATOM 2 1
λ
the nucleus of nucleus of nucleus series of lines named after the researchers
Electromagnetic spectrum : E2 - E1 > E3 - E2 > E4 - E3 > E5 - E4 and so on.
Charge -1.6´10 C-19 -19
1.6 ´10 C Neutral It is the arrangement of components of different types of Name of Wavelength n 1 n2 Region
Absolute mass (kg) 9.1´10-31 Series Derived Formulae of Bohr’s Theory
1.67 ´10-27 1.67 ´10-27 electromagnetic radiations in increasing order of wave-
1. Lyman 1 é 1 1 ù 1 n >1 UV (for n th
orbit)
Relative Mass J. J. Thomson E. Goldstein J. Chadwick length or decreasing order of frequency.
= RH ê 2 - 2 ú Energy (E n )
ATOMIC MODELS λ ê1 n2 ú
Wavelength(λ) Frequency (ν) ë û Speed (v n )
For hydrogen For H-like
Thomson Model Distance be-
Frequency (ν ) 2. Balmer 1 é 1 1ú ù 2 n>2 Visible 2
tween two con- = R ê - - 1312 - 1312 Z For hydrogen
Atom is spherical, in which positive charge is +vely Charged +vely Charged
velocity λ H
ê 2 2 2ú
n2 û kJ / mol kJ / mol 8
2.18 ´ 10
matter

ë n 2
matter
2
uniformly distributed. The electrons are em- secutive points = n cms-1
of a wave. wavelength 3. Paschen 1 é1 1 ùú 3 n > 3 IR n
bedded into it. Wave Number (ν ) = R ê - Radius (rn )
Rutherford’s Model λ H
ê 32
n 2ú
ë 2 û For hydrogen For H-like
For H-like
Different types of spectra : Wave Number
Atom is spherical, in which 4. Brackett 1 é1 1 ù 4 n > 4 IR 2 0.529 n 2 2.18´108
1 = R ê - ú 0.529 ´ n Å Å ´ Zcms-1

positive charge is uniformly Atomic spectra Molecular spectra (ν ) = λ λ H

ê 42 n22 ú
ë û Z n
distributed. The electrons Line spectra Absorption 5. Pfund 1 é1 1 ù 5 n > 5 far IR Limitations of Bohr’s Model
are embedded into it. Each line in spectra spectra = R ê - ú
Spectra λ H
ê 52 n22 ú • Mathematically, Bohr’s model explains only mono-
represents one ë û
electronic transition 6. Humphrey 1 é1 ù 6 n 6 far-far electronic atoms and fails to explain repulsion in
1 >
Atomic number (Z) =Number of protons (p)
Emission = RH ê 2 - 2 ú IR multielectronic atoms.
Band spectra spectra λ ê6 n ú
ë 2 û • It does not explain the distribution of electrons in
Mass number (A) = No. of protons (p) + No. of neutrons (n) Continuous spectra Discontinuous spectra orbits.
1 æ1 1 ö÷ 2
Number of neutrons (n) = A – Z Symbol of elements ZA X screen screen
Rydberg formula :ν = = RH çç 2 - 2 ÷÷ Z • It does not provide mathematical support to assump
λ çè n1 n2 ø÷
tion, h
Isotopes slit cloud
slit

where, mvr = n ´
2π
of gas
prism
prism
Atoms of same element having same atomic number but different RH is Rydberg constant and has a value equal to • It is against de Broglie and Heisenberg’s principles.
109677cm-1 • It does not explain the splitting of spectral lines
HT

mass numbers. e.g., Hydrogen - 11H,12 H,13 H

LIG RCE
U
SO
HT
LIG RCE
U absorption spectrum
under the influence of electric field (Stark effect)
SO

35 37
Chlorine - 17 Cl, 17 Cl continous spectrum Planck’s Quantum Theory : BOHR’S ATOMIC MODEL FOR HYDROGEN
Isobars screen and magnetic field (Zeeman effect)
• Definite amount of radiant • Around the nucleus there are circular re
Atoms of different elements having same mass number but differ- energy is emitted or absorbed DUAL NATURE OF RADIATION
40 40 40
slit gions called orbits or shells. • de Broglie has suggested that light can behave as a
ent atomic numbers. e.g., Ar, K, Ca prism
discontinuously in the form of Energy shell K L M N O... wave as well as like a particle. In 1924, de Broglie
hot gas
18 19 20

Isotones small packets, called quanta. n 1 2 3 4 5....

suggested that all microscopic particles such as elec
• Amount of energy associated ______________________________
Atoms of different elements containing same number of neutrons. emission spectrum
tron, proton and atoms, etc. also have dual character
14 15 16 with quantum of radiation, is Energy and distance from nucleus increase from K onwards
e.g., 6 C,7 N,8 O h h
proportional to frequency of • Every orbit has a fixed amount of energy so, de Broglie wavelength, λ = =
Black Body Radiation light i.e. it is also referred to as an energy level. mv p
Isodiaphers • Relation between Kinetic energy and wavelength,
An ideal body which hc • An electron revolves around the nucleus
Atoms having same isotopic number (i.e., no. of neutrons – no. of E µ ν E = h ν E = h
235 231 emits and absorbs radi- λ without any loss of energy in a particular λ =
protons = same) e.g., 92 U,90 U 2´ KE ´ m
ations of all wave- h = planck ' s constant (6.626´10-34 Js ) orbit of definite energy that is why orbit is
Isosters lengths or frequencies. incoming blue light
called stationary state also. Heisenberg’s Uncertainty Principle
Molecules having same number of atoms and electrons. e.g., • Angular momentum (mvr) in each orbit is It is impossible to determine simultaneously,
collector plate emitter plate

CO 2 , N 2O Photoelectric Effect quantised, the exact position and exact momentum (or
h velocity) of an electron. If the value of one is
When a beam of light of suitable wavelength falls on a clean metal plate in vacuum, electrons mvr = n = n here, h is Planck’s constant.
determined with certainty, the accuracy in
are emitted from the surface of metal. This phenomenon is known as photoelectric effect 2π
vacuum n : 1 2 3 4 determining the other value is compromised.
electrons get to collector plate
h h h h h h ∆x = uncertainty
∆ x .∆ p ³ ; ∆x.m ∆v ³
hν = hν 0 + 1/ 2mv 2
hν 0 = Minimum energy required to eject an electron = work function ( w) + - mA mvr : 1.5 2 4π 4π in position
2π π π π
∆x = uncertainty in position,
Ammeter
V