Electron Configuration
Chemistry
Chapter 4 – Section 2
• The Quantum Model of the Atom
I. Introduction
• Bohr’s Model did not make sense
to most scientists, who felt that the
electron should exist at any
distance from the nucleus,
depending on energy, rather than in
certain levels
II. Electrons as Waves
• A. De Broglie proposed that an
electron, like light, might exist as a
particle and a wave
• 1. A wave confined to a certain space
can only have certain frequencies
• a. This corresponded to Bohr’s orbits
• b. It also corresponded to the specific
frequencies produced in line-emission
spectrums
• 2. Beams of electrons can also be bent or
refracted, or experience interference, just as
light does
• a. Diffraction – the bending of a wave around
the edge of an object or opening
• b. Interference – the overlapping of waves,
which either increases or decreases each the
waves’ energy
III. Heisenberg Uncertainty
Principle
• A. The dual wave-particle nature of an electron
made many scientists uneasy, because they
could not pin point where the electron would be
located in the atom
• B. Heisenberg proposed that electrons and
photons have about the same energy
• 1. Since photons are used to knock electrons off
metal (and thus, detect the electrons), the exact
location of an electron cannot be determined
with certainty
• 2. The Heisenberg Uncertainty Principle – it is
impossible to determine the location and speed
of the electron or photon at the same time
IV. The Schrodinger Wave
Equation
• A. Schrodinger developed an equation to
show that electrons behave as waves (only
certain frequencies would solved the
equation)
• B. Together, Heisenberg and Schrodinger
laid the foundation for our modern quantum
theory – the mathematical description of the
wave properties of electrons and other small
particles
• 1.Solutions to the equations are called wave
functions
• 2.They do not locate the electron, but merely give
the probability of locating it
• 3.This showed that electrons do not travel in neat
orbits around the nucleus as Bohr described, but
exist in certain regions called orbitals
• 4.Orbital – a three-dimensional region around the
nucleus that indicates the probable location of the
electron
• 5.Orbitals can have
• different shapes and sizes
V. Atomic Orbitals and
Quantum Numbers
• A. Quantum numbers are used to describe
orbitals and the properties of electrons in
them
• 1.The first three quantum numbers indicate:
• a.Main energy level of the orbital
• b.Shape of orbital
• c.Orientation of orbital
• 2.The fourth quantum number is the spin quantum
# and indicates the fundamental spin state of the
electron
• B.Principal Quantum Number (n)
• 1.This is the main energy level of the electron
• 2.As (n) increases, electron energy and distance
from the nucleus increases
• 3.Electrons with the same (n) value will be in the
same energy level
• 4.(n2) is the total number of
• orbitals in each energy level
• C.Angular Momentum Quantum Number
• 1.These sublevels are orbitals of different shapes
• 2.(l) indicates the shape of the orbital and is
called the (l) value
• 3.If the (l) value is s, then the shape is spherical
• 4.If the (l) value is p, then the shape is a dumbbell
• 5.If the (l) value is d, then the shape is a clover
leaf
• 6.If the (l) value is f, then the shape is a flower
petals
p
d
f
D. Magnetic Quantum Number
• 1.Orbitals can be the same shape, but have
different orientations (axes)
• 2.Magnetic Quantum Number (m) – indicates the
orientation (or axis) of the orbital
• 3.The (m) value = + l to -l
E. Spin Quantum Number
• 1.These values can be +1/2 or –1/2
• 2.This indicates the spin state of the
electron
• 3.Any orbital can hold 2 electrons, but they
must have opposite spin states
Chapter 4 – Section III
• Electron Configuration
electron
neutron
proton
I. Electron Configuration
• A. Bohr’s model of the atom only
described electron arrangement in the
Hydrogen atom
• B.The quantum model of the atom
describes electron arrangement for all
atoms
• 1. Electron Configuration – the
arrangement of electrons in an atom
• 2. Electrons always assume the lowest
possible energy state
II. Rules Governing Electron
Configurations
• A. Aufbau principle – an electron occupies the
lowest energy orbital that has a space for it
• B. Pauli exclusion principle – no two electrons in
the same atom can have the same 4 quantum
numbers
• 1. No two electrons can be in the same place at the
same time
• 2. If two electrons occupy the same orbital, then
they must have opposite spin states
• C. Hund’s rule – orbitals of equal
energy will have one electron each until
all orbitals have one before a second
electron enters an occupied orbital
• 1. This minimizes repulsion between
electrons
• 2. This allows the electron to have the
lowest energy possible
electron
neutron
proton
III. Representing Electron
Configurations
• A. There are 3 methods of electron
configuration notation
• 1. Two are used for elements in the
1st two periods
• 2. The third is used for elements in
the 3rd period and higher
1s2 2s2 2p6 3s2 3p5
OR
[Ne]3s2 3p5
1s2 2s2 2p6 3s2 3p6 3d10 4s1
OR
[Ar]3d10 4s1
• B. Orbital Notation
• 1. A blank line (___) represents an orbital
Carbon is paramagnetic
with no electrons
• 2. An orbital with 1 electron is represented
with___
• An orbital with its maximum number of two
electrons is represented with _____(shows
the opposite spins)
• 4. Each line is labeled with the (n) and (l)
is
value Neon
diamagnetic
• C. Electron Configuration Notation – each
orbital letter has a superscript to show how
many electrons are in the level
• D. Elements of the 2nd Period
• 1. Highest occupied energy level – the
energy level farthest from the nucleus that
contains electrons
• 2. Inner shell electrons – those electrons not
in the highest energy level
• 3. Octet of electrons – highest energy level is
filled with 8 electrons
• E. Elements of the 3rd Period
• 1. 1st 10 electrons of any atom in the period are the
same as Neon
• 2. Noble Gases – the Group VIII (or 18) elements
• 3. Noble Gas Notation – also called abbreviated
notation
• a.Use the symbol for the noble gas in brackets [Ne]
that is previous to the element
• b.Then continue with the electron configuration
notation
• 4. Noble Gas Configuration – the outermost
energy level containing 8 electrons (Helium is the exception)
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F. Elements of the 4th Period
1. 4s fills 1st
2. 3d fills 2nd
3. 4p fills 3rd
G. 5th Period Elements
1. 5s fills 1st
2. 4d fills 2nd
3. 5p fills 3rd
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H. Elements of the 6th and 7th Periods
1. 6s fills 1st
2. 5d fills 2nd in La
3. 4f fills 3rd
4. The rest of 5d fills 4th
5. 6p fills 5th
6. 7s fills 6th
7. 6d fills 7th in Ac
8. 5f fills 8th
9. Rest of 6d fills 9th
1s
2s
2px
2py
2pz
3s
3px
3py
3pz
3dxy 3dxz
3dyz 3dx2y2
4s
4px
4py
4pz
4dxy
4dxz
4dyz 4dx2y2
4fz3
4fxz2
4yz2 4fy(3x2-y2)
4fx(x2-3y2) 4fz(x2-y2)
3dz2
4fxyz
4dz2
• 1s2 2s2 2p6 3s2 3p5
•
OR
•
[Ne]3s2 3p5