FACT:Chemical reactions
happen because electrons are shared or transferred from one substance to another
MAX NUMBER OF ELECTRONS IN AN ENERGY LEVEL
ENERGY LEVEL MAX # OF ELECTRONS
1 22 83 184 325 50
Write a mathematical equation that allows us to predict the Max # if we
know the energy level (n)
ENERGY LEVEL MAX # OF ELECTRONS
1 2
2 8
3 18
4 32
5 50
Max # = …n…
Equation to calculate Max # of e-
2n2
Where n is any energy level
There are 4 Quantum #s and those #s are
used to describe where an electron is likely to be found at any given
time
The first number we already know…
The Principle Quantum #
1st Quantum #Principle Quantum #
Specifies the energy level that the electron
is on
But this doesn’t explain why K’s last electron goes into the
4th energy level instead of the 3rd
2nd Quantum #
Specifies the shape of the sub-energy level
s and p Sub Energy Levels
III. Quantum Mechanical Model: Atomic OrbitalsE. Shapes of orbitals
d orbitals
ORBITALSpace occupied by a pair of electrons
Four Sub-Energy LevelsSub NRG
LevelShape Max # of
electrons# of
Orbitals
s Sphere 2 1
p Dumbbell 6 3
d 4-Lobed 10 5
f 6-8 Lobed 14 7
Sub-Energy Levels
So why do electrons fill in like they do?
i.e. why is K’s last electron in the 4th NRG level?
2 Factors Influencing Electron Placement
1.Energy Level- Closer to nucleus=easy
2. Subenergy level (shape) - spdf
Electron ConfigurationA detailed way of
showing the order in which electrons fill in around the nucleus
Electron Configuration Symbols
5f 3
Energy LevelSub-Energy
Level
# of e- in sub-energy
level
Electron Configuration PT
K
K: 2s21s2 4s13s22p6 3p6
Bohr Models
vs. e- Configs
Write the e- config for:
H:1s1
He: 1s2
Li: 1s22s1
K: 1s22s22p63s23p64s1
Again…Why are we concerned so much about electrons?
So do we really need to know
about all of the electrons?
Valence Electrons
Electrons in the outermost energy
level (involved in chemical reactions)
Noble Gas ShortcutK: 1s22s22p63s23p64s1
K: [Ar] 4s1
So what is different?
Aufbau Principle
All lower energy sublevels must be full before high energy sublevels begin
filling in
Steps for writing NGSC
1. Write the noble gas preceding the desired element [in brackets]
2. Carry on as usual
With only the first two Quantum #s, do we have as much information as possible as to where the electrons are likely to be
found?
3rd Quantum #m or magnetic Q#
Specifies the orientation of an orbital in space
4th Quantum #s or spin Q#
Spin of an electron on its own axis
Quantum Review1st Q#: Energy Level
2nd Q#: Shape of sub3rd Q#: Orientation of Orbital
4th Q#: Spin of e-
Quantum ReviewPrinciple (n): 1, 2, 3, 4, …
Azimuthal (l): 0, 1, 2, 3
Magnetic (ml): …-2, -1, 0, 1, 2
Spin (ms): +1/2 or -1/2
Pauli Exclusion Principle
No 2 electrons can have the same set of 4
quantum numbers
Arrow-Orbital Diagrams
A way to show orbital filling, spin,
relative energy
Hund’s RuleMost stable
arrangement of electrons is the one with the maximum number of
unpaired electrons
Arrow-Orbital DiagramsE
ner
gy
1s2s 2p
3p3s4s
3d
Lewis Electron Dot Diagrams
The easiest way to represent the # of valance electrons
Steps for writing electron dot diagrams
1. Write the element’s symbol
2. Write out e- config
3. Count # of valence e-s (1-8)
4. Place same # of dots as e- around symbol
Order to fill in an e- dot
Bm
12
34
5
6
7
8
What up?
Bm
12
Why do 1 and 2 fill in on the same side?
Who do 1 and 2 represent?
What up?
Bm
34
5
6
78
Who do 3-8 represent?
Why do 3,4,5 and 6,7,8 fill in on different sides?
What up?
Bm
34
5
6
78
Why will you never have
more than eight dots?
12
Examples of Lewis Electron Dots
What is different between the dot diagrams below and the
ones you’ve just seen?
The one you saw accounts for Quantum #s, this way doesn’t!
Flame Tests
Certain elements emit specific wavelengths of light when the electrons fall from outer energy levels back to their ground state.
The Electromagnetic Spectrum
Line Spectra of Excited Atoms• Excited atoms emit light of only certain wavelengths
• The wavelengths of emitted light depend on the element.
H
Hg
Ne