Transcript The Quantum mechanical model of the atom

Section 3.2 – page 174
THE QUANTUM MECHANICAL
MODEL OF THE ATOM
HTTP://ED.TED.COM/LESSONS/THE-UNCERTAIN-LOCATION-OF-ELECTRONS-GEORGE-ZAIDAN-AND-CHARLES-MORTON
De Broglie
 Proposed the dual nature of light; it could act
as a particle or a wave.
 http://ed.ted.com/lessons/particles-andwaves-the-central-mystery-of-quantummechanics-chad-orzel
Schrodinger
 Published the wave equation.
 Determined the quantum numbers (n, l and ml).
 The model of the atom where electrons are
treated as waves is referred to as the Quantum
Mechanical Model.
 http://ed.ted.com/lessons/what-can-schrodinger-s-
cat-teach-us-about-quantum-mechanics-josh-samani
 http://ed.ted.com/lessons/schrodinger-s-cat-athought-experiment-in-quantum-mechanics-
chad-orzel
How you probably feel right
now…..
Born
 Showed that wave functions (based on the
wave equation) could be used to determine
the probability of finding an electron at any
point within the region of space described by
the wave function.
Heisenberg
 Showed that it is impossible to know both the
position and momentum of a particle with
precision – Heisenberg Uncertainty Principle.
 Hence, we can picture the electrons like a
cloud around the nucleus.
 Higher density of the cloud = higher
probability of finding an electron in that
location.
Summary
 Motion of electron around nucleus described
by wave equation (same as waves in a fluid).
 The solution to the wave equation is a wave
function.
 If we could determine the wave function for
every electron in an atom, we would have a
complete “picture” of the atom.
 BUT…wave equations are so complex, this is
impossible! We can only approximate by
predicting.
Quantum Mechanical Model
 Electrons belong to different layers, or shells
at different distances from the nucleus.
 The farther a shell is, the more electrons it
can hold and the greater the energy of the
electrons.
 Within each shell, electrons are grouped in
pairs into regions of space called orbitals –
the space where an electron spends 90-95%
of its time.
 Orbitals can have different shapes depending
on the energy level to which it belongs.
 Each orbital can be described mathematically
by its wave function.
 There are four kinds of orbitals: s, p, f, d.
Quantum Numbers
 Describe specific properties of electrons in
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atoms.
n = principle quantum number = orbital’s
energy level and relative size
l = describe orbital’s shape (subshell)
ml = describe orbital’s orientation in space
(magnetic quantum number).
ms= describes behaviour of a specific electron
in an orbital (spin quantum number).
Describing Atomic Structure
using Quantum Numbers
 If an atom has n=1, what are the possible atomic
structures? How many are possible?
 n=1 means electrons exist ONLY in the first energy
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level.
Therefore, there is only one possible shape, so l=0.
This is the spherical shape (s orbital).
Electrons in the l=0 (s orbital), only have 1 orientation
therefore ml=0.
The electrons can spin in either direction around its
axis so the possible ms values are +1/2 and -1/2.
In this case, there are only 2 different atomic
structures because only 2 electrons can exist in the
first energy level.
 If an atom has n=2, what are the possible atomic
structures? How many are possible?
 n=2 means electrons are in the first AND second
energy level.
 Therefore, there are 2 possible orbital shapes
(sublevels), l=0 (s) and l=1 (p).
 The s-orbital only has electrons in 1 orientation so
ml=0 but the p orbitals have electrons in 3 different
orientations so ml=-1, 0, 1.
 Each electron can spin in either direction around its
axis so the possible ms values are +1/2 and -1/2. Each
electron can only have 1 ms value and paired electrons
must have opposite spins.
 In this case there are 8 possible electron
configurations for n=2 (similar to how there
are only 8 electrons allowed in the 2nd energy
level).
 2 electrons possible in the 2s orbital
 6 electrons possible in the p orbitals (2 electrons in
each of the 3 orientations.)
Pauli Exclusion Principle
 2 electrons can exist in an orbital.
 They must be of opposite spins (+1/2, -1/2)
 So, no 2 electrons in an atom have the same 4
quantum numbers.
Textbook
 Reading – pages 174-178
 Practice – page 179 - #1-10