Engineering Physics Bs-124

Engineering Physics BS-124

Lecture -03

 Instructor

Atif M.Khokhar Assistant Professor

Main Contents • • • • • •

Review of the last Lecture Atomic Number and Atomic Mass Isotopes de Broglie Waves Home work Quiz

Atomic structure • When we finish this part you will be able to; • Define atomic number & mass number and isotopes • Under stand Wave nature of matter • Describe Wave Model about atom

HELIUM ATOM Shell

proton

+ -

N

N

+

electron What do these particles consist of? Home Work

-

neutron

ATOMIC STRUCTURE Particle

Charge

proton

+ ve charge

neutron

No charge

electron

-ve charge

ATOMIC STRUCTURE

4

He

2

Atomic mass /Mass no.

“A”

the number of protons and neutrons in an atom

Atomic No.

“Z”

the number of protons in an atom

number of electrons = number of protons

Isotopes The Isotopes of the element have the Same Atomic no. “Z” but different Mass no. “A”

mass number (m)

1

atomic number (z)

1

1 proton 1 electron

H

Isotopes

mass number (m)

2

atomic number (z)

1

1 proton, 1 neutron 1 electron

H

Isotopes

mass number (m)

12

atomic number (z)

6

6 protons, 6 neutrons 6 electrons

C

Isotopes

mass number (m)

13

atomic number (z)

6

C

6 protons, 7 neutrons 6 electrons

Quantum or Wave Mechanics

L. de Broglie (1892-1987)

• Light has both wave & particle properties • de Broglie (1924) proposed that all moving objects have wave properties. • For light: E = hν = hc / λ Therefore, mc = h / λ 2 • For and particles: E = mc for particles (Einstein) (mass)x(velocity) = h / λ

λ for particles is called the de Broglie wavelength

WAVE properties of matter

Electron diffraction with electrons of 5-200 keV

Davisson & Germer 1927

Na Atom Laser beams

λ = 15 micometers (µ m)

The new atom laser emits pulses of coherent atoms, or atoms that "march in lock-step." Each pulse contains several million coherent atoms.

Quantum or Wave Mechanics Schrodinger applied idea of ebehaving as a wave to the problem of electrons in atoms. Solution to WAVE EQUATION gives set of mathematical expressions called E. Schrodinger 1887-1961

WAVE FUNCTIONS, Ψ Each describes an allowed energy state of an e-Quantization introduced naturally.

de Broglie Waves • One of Bohr’s postulates was the angular momentum of the electron is quantized, but there was no explanation why the restriction occurred • de Broglie assumed that the electron orbit would be stable (i.e., allowed) only if it contained an integral number of electron wavelengths

de Broglie Waves in the Hydrogen Atom • In this example, three complete wavelengths are contained in the circumference of the orbit

• In general, the circumference must equal some integer number of wavelengths

– 2 π r = n λ ; n = 1, 2, …

de Broglie Waves in the Hydrogen Atom, cont. • • • •

2π r = n λ λ =h/(mev) 2π r =nh/(mev) mevr = nh/(2π ) [angular momentum of circular orbit]

• This is precisely the quantization of angular momentum condition imposed by Bohr

Quantum Mechanics and the Hydrogen Atom • One of the first great achievements of quantum mechanics was the solution of the wave equation for the hydrogen atom • The significance of quantum mechanics is that the quantum numbers and the restrictions placed on their values arise directly from the mathematics and not from any assumptions made to make the theory agree with experiments

Home Work

•Draw the energy level diagram for Hydrogen Atom for N= 10. •You can use lead pencil and black & blue

Quiz Name : Department: Section: Date: Marks:

Quiz-B • According to Classical Theory electron radiate energy while moving around the nucleus and at last spiral into the nucleus and making atom unstable. • But atom is stable, why? Give reason and who proposed this idea. • You can draw figure to support your answer