quantum mechanics - school of chemistry and...
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Week 5 CHEM 1310 - Sections L and M 1
Quantum Mechanics
Quantum Numbers– Pauli Exclusion Principle– Aufbau Principle– Hund’s Rule
– Valence Electrons
Periodic Table Trends– Ionization Energy– Electron Affinity– Atomic Radii
Week 5 CHEM 1310 - Sections L and M 2
Pauli Exclusion PrincipleIn an atom, no two e- can have the same set of quantum #’s.
nl
mlms
Week 5 CHEM 1310 - Sections L and M 3
Aufbau PrincipleElectrons add one by one to atomic orbitals to“build up” from lower to higher energy states.
orbitals
Each orbital can hold 2 e-
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Week 5 CHEM 1310 - Sections L and M 4
Aufbau PrincipleElectrons add one by one to atomic orbitals to“build up” from lower to higher energy states.
“s” subshell can hold only 2 e-
“p” subshell can hold up to6 e-
Only 2 e- in the 2p subshell
Week 5 CHEM 1310 - Sections L and M 5
Hund’s Rule
When several orbitals are of equal energy, a singlee- enters each orbital before a second e- enters.
6C: 1s2 2s2 2px1 2py
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Week 5 CHEM 1310 - Sections L and M 6
Hund’s Rule
The spin of electrons filling orbitals of thesame energy level remain parallel untilelectron pairs can be formed.
7N: 1s22s22px12py
12pz1
8O: 1s22s22px22py
12pz1
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Week 5 CHEM 1310 - Sections L and M 7
Trends in the Periodic Table
Week 5 CHEM 1310 - Sections L and M 8
Valence Electrons
Electrons in theoutermost (i.e. highestenergy) shell of an atom
Directly involved inbonding
Number of valence e- issame as the Group # inthe Periodic Table
Increasing # of valence e- across period
Week 5 CHEM 1310 - Sections L and M 9
Valence Electrons
8O 1s2 2s2 2px2 2py
1 2pz1
1s
2s2pE
# of e- in the outer-most shell
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Notice that 2 of oxygen’s valencee- are unpaired!
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Week 5 CHEM 1310 - Sections L and M 10
PRS QuestionWho developed the theory that no two electrons can have
the same set of quantum numbers?
(1) Hund
(2) Aufbau
(3) Heisenberg
(4) Pauli
(5) Einstein
Week 5 CHEM 1310 - Sections L and M 11
PRS QuestionWho developed the theory that no two electrons can have
the same set of quantum numbers?
(1) Hund
(2) Aufbau
(3) Heisenberg
(4) Pauli
(5) Einstein
Pauli Exclusion Principle
Week 5 CHEM 1310 - Sections L and M 12
PRS QuestionWhat is the maximum number of electrons that can occupy
the orbitals with principle quantum number = 4?
(1) 2
(2) 8
(3) 18
(4) 32
(5) None of the above
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Week 5 CHEM 1310 - Sections L and M 13
PRS QuestionWhat is the maximum number of electrons that can occupy
the orbitals with principle quantum number = 4?
(1) 2
(2) 8
(3) 18
(4) 32
(5) None of the above
4s = 24p = 64d = 104f = 14
Sum = 32
Week 5 CHEM 1310 - Sections L and M 14
PRS Question
Which of the following elements has 4 valence electrons?
(1) Be
(2) Si
(3) P
(4) Al
(5) As
Week 5 CHEM 1310 - Sections L and M 15
PRS Question
Which of the following elements has 4 valence electrons?
(1) Be - 2
(2) Si
(3) P - 5
(4) Al - 3
(5) As - 5
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Week 5 CHEM 1310 - Sections L and M 16
PRS Question
How many valence electrons does Mg2+ have?
(1) 0
(2) 1
(3) 2
(4) 3
(5) 12
Week 5 CHEM 1310 - Sections L and M 17
PRS Question
How many valence electrons does Mg2+ have?
(1) 0
(2) 1
(3) 2
(4) 3
(5) 12
Mg is in Group 2(meaning 2 valence e-)
but Mg2+ has lostthem!
Week 5 CHEM 1310 - Sections L and M 18
Ionization Energy
Ionization energy is that required to remove an e- from agaseous atom or ion in the ground state.
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Week 5 CHEM 1310 - Sections L and M 19
Atomic Radius
The radius of an atom (r) is definedas half the distance between the nuclei in a molecule
consisting of identical atoms.
Week 5 CHEM 1310 - Sections L and M 20
Comparing Atomic Radii
Elements with very different # of e- can have similar atomic radii.
13 e-
88 e-
Distance inpicometers
1 x 10-12 m
Week 5 CHEM 1310 - Sections L and M 21
Atomic radiusincreases downa group
Atomic radiusdecreasesacross a period
Periodic Trends: Atomic Radii
smaller
larg
er
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Week 5 CHEM 1310 - Sections L and M 22
Next Week
Recap of Chapter 12– Summary of what to learn re: Quantum Mechanics– More practice questions re: QM
Begin Chapter 13: Bonding– Read entire chapter