Atomic Structure
(6 lectures)
Dr. Paul T. Maragh
Department of Chemistry
TEXT :
The Elements of Physical Chemistry –
P.W. Atkins, J. De Paula
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CHEM1901: Atomic Structure
(6 lectures)
•Important part of the core course
•Concepts are employed in the subsequent sections
on Physical, Inorganic (e.g. bonding and antibonding
orbitals) and Organic Chemistry (e.g. hybridization).
This covers basic and fundamental principles which
are common to all areas of Chemistry.
•Do not form, or create, an imaginary boundary which
separates the different disciplines of Chemistry, but
search for and make the links which will make
understanding the different topics more enjoyable.
2
The Hydrogen Atom
Classical view
+
-
Electron moving about proton
Charge:
Proton = +e
Electron = –e
e = 1.602 x 10-19 C, the fundamental charge. Is the charge
carried by a single proton.
3
Types of Forces
• Electrostatic (Coulombic) Force (between 2 charged particles)
q1
q2
q1 q 2
FE 
r
4o r 2
• Gravitational Force (between two masses)
m1
m2
r
Gm1 m2
FG 
r2
o = 8.854 x 10-12 C2 J-1 m-1 is the permittivity of a vacuum
G = 6.672 x 10-11 N m2 kg-2 is the Gravitation Constant
4
H – Atom (cont’d)
Rotating systems:
r1
r2
m1r1 = m2r2
m1/m2 = r2/r1
m1
Centre of
Proton
mp = 1836 me
m2
Centre of
Mass
Centre of
Mass
..
electron
proton
• Assume: proton stationary with electron orbiting it.
• If position q, and velocity v are known simultaneously
then future motion can be predicted.
• NOT SO for the electron!
5
Heisenberg Uncertainty Principle
• If q and v are the position and velocity of an electron,
respectively, and q and v are their respective
uncertainties, then:
p (= mv) is the linear momentum, and m v = p
h, Planck’s constant
= 6.626 x 10–34 J s
me, mass of the electron = 9.109 x 10-31 kg

h
2
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Locating the electron?
• Electromagnetic radiation has photons
• Energy of a photon is given by E = h
• Effect of light photon on flight of mosquito?
• Effect of high energy photon on path of electron?
• Locating the electron with pinpoint accuracy (i.e. q = 0)
would require v = , which would mean that we know
nothing at all about its velocity.
• Uncertainty exists for all systems.
• mmoon = 7.4 x 10 22 kg, q.v is negligible;
• me = 9.1 x 10-31 kg, q.v is large, path of the electron cannot
be calculated (with reasonable accuracy).
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ALL IS NOT LOST!
• What can we measure, that does not depend on
simultaneous position and velocity of an electron?
• ENERGY!
• Law of Conservation of Energy:
Energytotal = Kinetic Energytotal +
(due to motion)
Potential Energytotal
(due to attraction)
• Make observations on Constant Energy H-Atom
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