Locating Electrons
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Newtonian Mechanics – describes objects at
ordinary velocities (classical mechanics)
Quantum Mechanics – describes particles at
velocities near that of light (subatomic particles)
Quanta – a packet of nrg
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It is impossible to know both the location and
velocity of an electron at the same time.
◦ To see an e- we would have to bounce light off of it
which would change its velocity and in turn its
position.
 Ex: helium-filled balloon in a dark room
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In 1926, he treated e- as waves, giving us the
e- cloud model.
◦ Radial Probability of Electrons
The area of highest
probability forms
the e- cloud.
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Principle Quantum Number (n)
Sublevel (l)
Orbital (m)
Spin (s)
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Energy levels are a particular distance from
the nucleus
# e- =
2
8
18
32
50
n=
1
2
3
4
5
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The maximum number of electrons in
each nrg level is 2n2
◦ At n = 1, there can be 2(1)2 = 2 e-
◦ At n = 2, there can be 2(2)2 = 8 e◦ At n = 3, there can be 2(3)2 = 18 e-
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Tells the shape
Each nrg level has a # of sublevels = to n
Energy Level
(n)
# Sublevels
Sublevels
1
1
1s
2
2
2s, 2p
3
3
3s, 3p, 3d
4
4
4s, 4p, 4d, 4f
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The 3rd quantum number (m) tells which
orbital and electron occupies.
One pair (2e-) of electrons can occupy each
orbital
◦ s sublevels have 1 orbital (2e-)
◦ p sublevels have 3 orbitals (6e-)
◦ d sublevels have 5 orbitals (10e-)
◦ f sublevels have 7 orbitals (14e-)
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** each orbital can hold UP TO 2 e-**
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Indicates direction of spin of e◦ -1/2 , +1/2
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(clockwise, counterclockwise)
Pauli Exclusion Principle states that no two
electrons in an atom can have the same set of
4 quantum numbers.
◦ The two e- in an orbital must have opposite spins.
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Helium has 2 electrons
◦
◦
◦
◦
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n=1
l =s
m=1
s = 1 up, 1 down
Helium’s electron configuration would be:
Principle
Quantum #
1s
2
# of e-
Sublevel
 Li
N
 Ne
 Na
2
1s 2 s
1
2
2
3
2
2
6
1s 2s 2 p
1s 2s 2 p
1s 2s 2 p 3s or Ne3s
2
2
6
1
1
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Degenerate orbitals have the same nrg
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
7p
3d
4d
5d
6d
7d
4f
5f
6f
7f
-
Sublevels fill in order of increasing nrg
-
1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p
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What is the electron configuration for:
◦ Cl – 17
2
2
6
2
1s 2s 2 p 3s 3 p
5
or
2
[ Ne]3s 3 p
5
◦ Pb - 82
1s 2 2s 2 2 p 6 3s 2 3 p 6 4s 2 3d 10 4 p 6 5s 2 4d 10 5 p 6 6s 2 4 f 14 5d 10 6 p 2
or
2
14
10
[ Xe]6s 4 f 5d 6 p
2
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e- first occupy the lowest possible nrg level
available.
Electron Dot Notation – show only valence e-,
those in the outer most nrg level
◦ ONLY UP TO 8e◦ 8 e- = stable
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Valence electrons – e- in the highest nrg levels
◦ These e- are what form bonds
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Examples:
H
He
Li
C
Be
Mg
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Only show valence electrons
Dots are either placed 1 on each side or in
pairs.
◦ Never more than 2 per side
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This is why lithium has only one dot and why
carbon can have 2 dot notations.
Li
Li
C
or
C
C
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What would the electron dot notation be for
titanium?
Ti = 22e- BUT only 2 valence eElectron Configuration Notation
2
2
6
2
6
2
1s 2s 2 p 3s 3 p 4s 3d
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Electron Dot Notation
Ti
2
Valence e-
-d’s are NEVER valence e-, they
ALWAYS fill after a high nrg level
-Same for f’s
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Show all orbitals with electrons
Electrons represented as up and down arrows
Arrows must be opposite within orbitals
Nitrogen (7)
1s
2s
2p
1s
2s
2p
Fluorine (9)
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Single electrons with the same spin must
occupy each equal-energy orbital before
additional electrons with opposite spins can
occupy the same orbitals.
Principle Sublevel Orbitals Orbitals eQuantum
Per
Per
Per
Number
Sublevel Energy Sublevel
Level
1
s
1
1
2
2
s
p
1
3
3
s
p
d
1
3
5
4
s
p
d
f
1
3
5
7
4
9
16
2
6
2
6
10
2
6
10
14
ePer
Energy
Level
2
8
18
32
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Quantum Mechanical Model – describes and
electron as having a particular amount of
energy, depending on its location.
Electron clouds give you the highest
probability of locating and electron.
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Excited state – electrons in a higher than
normal energy state.
Nitrogen: 1s2 2s2 2p3 (ground state)
1s2 2s2 2p2 3s1 (excited state)
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Lose or gain e◦ Anions – are negatively charged, having gained e◦ Cations – are positively charged, having lost e-
** atoms will gain or lose e- to become more stable**
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Na: 1s2 2s2 2p6 3s1
Na+: 1s2 2s2 2p6
◦ Alkali metals, like Na, want to lose their 1 valence
e- to become stable.
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Cl: 1s2 2s2 2p6 3s2 3p5
Cl-: 1s2 2s2 2p6 3s2 3p6
◦ Halogens, like Cl, want to gain a valence electron to
become stable.
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1s
Filled and half-filled sublevels are more
stable than partially filled sublevels.
2s
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2p
3s
3p
4s
3d
This Cr takes an e- from 4s to put one e- in
each of its 3d orbitals and Cu takes a 4s to fill
each of its 3d orbitals
Orbitals are stable when either full or half-full