Transcript Lecture 7

Chemistry 103
Lecture 7
Outline
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I. Electronic Structure (CH5)
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Orbitals/Quantum Numbers
Electron Configurations
EXAM I PRACTICE KEY POSTED
In glass case by office (CHE118)
Classical Mechanics
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There is no limit to the number of
observables we can measure simultaneously
These observables are continuous
Quantum Mechanics
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Unfortunately, extremely small particles
(electrons) do not follow the laws of classical
(Newtonian) physics. The new physics that
mathematically treats small particles is called
Quantum Mechanics.
Electronic Structure Quantum Mechanics
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Nature of Electrons in Atoms
Energy Level Changes
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An electron absorbs energy to
“jump” to a higher energy level.

When an electron falls to a
lower energy level, energy is
emitted.

In the visible range, the emitted
energy appears as a color.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Periodicity of Periodic Table
Objective: Placing Electrons about the Nucleus
of an Atom for a Particular Element.
MODEL DEVELOPED
(Quantum Numbers)
APPLICATION
(Electron Configurations)
Quantum Numbers - The Model
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Shell (n)
l=0.
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Subshell (l)
l=1
l=2
l=3
Electron Orbitals (n & l )
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Orbital
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Region of space where two electrons are likely to
be found (90% probability)
Have different shapes depending on which
subshell (l quantum number) they are in
Orbital Shapes
Quantum Numbers - The Model
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Shell (n)
l=0.
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l=1
l=2
l=3
Subshell (l)
Example: l=1, ml=-1,0,1
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Orientation (ml)
How many orbitals of a given type are
there?
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Quantum number: ml = -l, -l +1,… 0 … +l
Covers the entire positive and negative range of “l” in increments
of “1”.
Example: l = 1 (p orbital type)
ml = -1, 0 , 1
(there are 3 values, that label 3 different “p” orbitals - different
orientations in space)
p Orbitals
A p orbital
•
Has a two-lobed shape
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Is one of three p orbitals that make up each p sublevel
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Increases in size as the value of n increases
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Electron Orbitals
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Orbitals
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There are a different number of orbitals for each
subshell (l ) type:
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In an s subshell (l=0), there is 1 orbital
In a p subshell (l=1), there are 3 orbitals
In a d subshell (l=2), there are 5 orbitals
In a f subshell (l=3), there are 7 orbitals.
Electron Spin
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The Maximum Number of Electrons any
single orbital can hold is two.
They are distinguished from each other by a
Quantum Number called “spin”. One electron
will be given the quantum number
+1/2 (
) and the other -1/2 ( ).
Learning Check
Indicate the number of electrons each will hold:
A. 4s sublevel (n = 4, l = 0)
(ANSWER=2)
B. 3d sublevel (n = 3, l = 2) (5 orbitals of 3d) (ANSWER = 10)
C. n = 3
(3s, 3p, 3d)
(ANSWER = 18)
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Summary of Model
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Electron Orbitals (n (shell)
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Number of orbitals (l
l (probability))
ml (orientation))
Using the Orbital Model
ELECTRON CONFIGURATIONS &
THE PERIODIC TABLE
Writing Electron Configurations
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Electron configurations tells us which energy levels the
electrons for each element are located.
THREE GENERAL rules for placing electrons about the
nucleus:
Writing Electron Configurations
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Electron configurations tells us which energy levels the
electrons for each element are located.
THREE GENERAL rules for placing electrons about the
nucleus:
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1. Electrons fill orbitals starting with lowest
energy first.
Writing Electron Configurations
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Electron configurations tells us which energy levels the
electrons for each element are located.
THREE GENERAL rules for placing electrons about the
nucleus:
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1. Electrons fill orbitals starting with lowest
energy first
2. There can be no more than 2 electrons in any
one orbital.
Aufbau Diagrams
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1s
2s
3s
4s
5s
6s
7s
2p
3p 3d
4p 4d 4f
5p 5d ….
6p …..
Electron Configurations
Placing electrons for an atom in orbitals by order of
increasing energy
(lowest->highest)
H
He
Li
Subshell Energy Order
How will you
remember the energy
order of the subshells?
Use the periodic table!
Subshells and the Periodic Table
Practice: Electron Configurations
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S
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Ge
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Rb
Names of Some Representative
Elements
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Several groups of representative elements are known
by common names.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Abbreviated Electron Configurations
An abbreviated (noble gas shorthand) configuration shows
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The symbol of the noble gas in brackets that represents
completed sublevels
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The remaining electrons in order of their sublevels
Example: Chlorine has a configuration of:
1s2 2s2 2p6
3s2 3p5
[Ne]
The abbreviated configuration for chlorine is:
[Ne] 3s2 3p5
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Practice: Electron Configurations
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S
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Ge
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Rb