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Atomic Structure
Lecture 1
Prof. James Sullivan
email: [email protected]
web: http://people.physics.anu.edu.au/~jps107/
I will post lecture slides on this site AFTER the
lecture.
Atomic Structure
Assessment
Two assignments – 20% each
Exam – 60%
No assigned textbook
Recommend:
Halliday, Resnick and Walker (Fundamentals of
Physics)
Eisberg and Resnick (Quantum Physics of Atoms,
Molecules, Solids, Nuclei and Particles)
Atomic Structure
Early models of the atom
Greek origin – “atomos”
English meaning – “indivisible”
Cannot be divided
Are atoms hard spheres?
When can we think of them as hard spheres?
Atomic Structure
Early models of the atom
“Plum pudding” model – J. J. Thomson
Electrons are a part of atoms
Atoms must be made of positive and negative
charges
Atomic Structure
Early models of the atom
Rutherford gold foil experiment
Alpha particles
What is an alpha particle?
How big is it – relative to an electron?
What will happen?
Atomic Structure
?????
Early models of the atom
What happened:
Atomic Structure
Early models of the atom
Rutherford model
Problems?
Atomic Structure
Early models of the atom
The Bohr model
Electrons move in circular orbits – Coulomb
potential
Some orbits are stable – no radiation
Radiation emitted when electrons transit from
higher energy level to lower energy level
hf = Ei – Ef
Orbit size determined by quantisation of angular
momentum
mvr = nħ
ħ = h/2π
Atomic Structure
Quantisation
Max Planck
Black body radiation
Classical description
I (λ , T ) =
2πckT
Problem???
Atomic Structure
λ4
Black body problem
Planck’s formula
2πhc 2
I (λ , T ) = 5 hc / λkT
λ (e
− 1)
h=6.626 x 10-34 Js
Radiation emitted in discrete units of energy
En=nhf
n=integer (quantum number), f=frequency
Molecules emit/absorb energy in discrete units
Has to change quantum states
No energy emitted or absorbed otherwise
Atomic Structure
Bohr model
Electrons move in circular orbits – Coulomb
potential
Some orbits are stable – no radiation
Radiation emitted when electrons transit from
higher energy level to lower energy level
hf = Ei – Ef
Orbit size determined by quantisation of angular
momentum
mvr = nħ
Atomic Structure
ħ = h/2π
The Bohr model
E=K+U
E – total energy, K – kinetic energy, U – potential
energy
U = qV = -ke2/r
k = 1/4πε0
Coulomb attractive force – F = ke2/r2
Centripetal acceleration – a = v2/r
F = ma
K=?
Atomic Structure
Bohr model
Total energy of the atom:
E = -ke2/2r
Negative value – bound system
Remember – mvr = nħ and K = mv2/2 = ke2/2r
r=?
rn = n2ħ2/mke2
n = 1, 2, 3, 4, …….
r1 = a0 = ħ2/mke2 – Bohr radius
Atomic Structure