1. Quantum Theory and the Electronic Structure of Atoms
Chapter Seven
Quantum Theory and the Electronic Structure of Atoms

2. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
Bohr’s greatest contribution to science was in building a simple model of the atom.
It was based on understanding the SHARP LINE SPECTRA of excited atoms.
Niels Bohr ( )
(Nobel Prize, 1922)

3. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
Emission spectra is either continuous or line spectra of radiation emitted by substances.
Continuous is a common feature to the emission spectra of the sun and of a heated solid; that is, all wavelengths of visible light are represented in the spectra.

4. Bohr’s Theory of the Hydrogen Atom
Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom

5. Line spectra is the light emission only at specific wavelengths.
Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
Emission spectra is either continuous or line spectra of radiation emitted by substances.
Continuous is a common feature to the emission spectra of the sun and of a heated solid; that is, all wavelengths of visible light are represented in the spectra.
The emission spectra of atoms in the gas phase do not show a continuous spread of wavelengths from red to violet; rather, the atoms produce bright lines in different parts of the visible spectrum.
Line spectra is the light emission only at specific wavelengths.
Excited atoms emit light of only certain wavelengths
The wavelengths of emitted light depend on the element.

6. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
Emission spectrum of any atom is a finger print (lines appeared at specific wavelengths) H Hg Ne

7. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
Bohr postulated that the electron is allowed to occupy only certain orbits of specific energies and the energies of the electron are quantized.
According to Bohr the emission spectrum of the H atom results from: the hydrogen atom is energised then electron excited to higher energy orbit and then drop to a lower-energy orbit and emitting a quantum of energy ( a photon) in the form of light.

8. Bohr’s Theory of the Hydrogen Atom
Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom

9. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
The equation that represent the energies that an electron in hydrogen atom can occupy are given by:
RH is the Rodberg constant (2.18 x J), n is an integer called the principle quantum number (n= 1,2,3,…..).
when n =1 this is refer to as ground state or the ground level. Which refer to the lowest energy state of a system.
N=2,3,4…. Is called an excited state or excited level, which is higher in energy than the ground state.

10. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
The journey from a lower step to a higher step is an energy-requiring process.
Whereas movement from a higher step to a lower step is an energy releasing process.

11. If nf > ni → (+ve) → ΔE (+ve) → Energy is absorbed
Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
If nf > ni → (+ve) → ΔE (+ve) → Energy is absorbed
If ni > nf → (-ve) → ΔE (-ve) → Energy is emitted

12. Bohr’s Theory of the Hydrogen Atom
Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom

13. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
Bohr’s Theory of the Hydrogen Atom
Example:
What is the wavelength of a photon (in nm) emitted during a transition from the ni = 5 state to the nf = 2 state in the hydrogen atom?
ni=5, nf = 2 , λ=?

14. De Broglie deduced that the particle and wave
Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
The Dual Nature of the Electron
De Broglie suggested that particles such as electron can posses wave properties.
According to de Borglie, an electron bond to nucleus behave like a standing wave.
De Broglie deduced that the particle and wave
prosperities are related by the expression
Where λ wavelenght of moving particle, m mass (kg),
u velocity of moving particle.

15. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms
The Dual Nature of the Electron
Example
What is the de Broglie wavelength (in nm) associated with a 2.5 g Ping-Pong ball traveling at 15.6 m/s?
λ = ?, m= 2.5g = 2.5x10-3kg, u=15.6m/s
λ=1.7x10-31m = 1.7x10-22nm.

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