Chapter 5
Electrons in Atoms
Wave Nature of Light
•Wavelength (λ) – shortest distance between equivalent
points on a continuous wave (unit: m or nm)
• Ex: Crest to Crest or Trough to Trough
Wave Nature of Light
•Frequency (ν) – the number of waves that pass a given
point per second (unit: Hz or 1/s)
• 1 Hertz (Hz) = 1 wave per second
Electromagnetic Radiation
• form of energy with wave-like behavior
Wavelength and Frequency Relationship:
Inverse Relationship: Long Wavelength mean Low Frequency
Speed of Light
•ALL electromagnetic radiation moves at the
speed of light
• speed of light = c = 3.0 x 108 m/s
• Formula:
c = λν = (wavelength) x (frequency)
Sample Problem
•Microwaves are used to cook food and transmit
information. What is the wavelength of a microwave
that has a frequency of 3.44x109 Hz?
Given:
ν = 3.44 x 109 Hz
Find: λ = ?
c  3.00 x 10 m/s
8
Equation:
c  
c     
c

3 . 00  10
m
8
 
3.44  10
9
s  8 . 72  10  2 m
1
s
Electromagnetic Spectrum
• shows all forms of electromagnetic radiation
(pg 139)
Electromagnetic Spectrum
• shows all forms of electromagnetic radiation
(pg 139)
Emission Spectrum
•Ground State: lowest, most stable energy
state of an electron
•Excited State: has more energy than the
ground state
•Photon: particle of electromagnetic radiation
• Light is both a particle and a wave
Photon
•Every element has its own specific atomic
emission spectrum
• When an excited electron returns to the
ground state, it gives off a photon of
electromagnetic radiation.
• Electrons are located in the electron
cloud.
•The electron does not have a definite
path nor can it be specifically located, but
we can predict its whereabouts based on
probabilities called orbitals
Quantum Theory and Numbers
• gives an electron’s position in an atom
•4 quantum numbers
•
•
•
•
n
l
m
s
If we compared
Quantum Numbers
to an address then
Name
Principle QN
Quantum Numbers
Symbol
Definition
Details
n
Indicates the
average distance
of the electron
from the nucleus
n is the period
number (a
number between
1 and 7)
Subshell
indicates the
shape of the
orbital
Indicates the
orientation in
space (dependent
on the shape)
Shapes are
labeled by
letters (s,p,d,f)
state
Orbital QN
l
city
Magnetic QN
m
street
Spin QN
s
Side of street
Indicates the
direction of spin
of the electron
s = 1 orientation
p = 3 orientations
d = 5 orientations
f = 7 orientations
Spin is either
+1/2 or -1/2
Important note:
EVERY electron in an atom
has a specific, unique set of
the four quantum numbers!
n (Principle Quantum #)
•Discovered and presented by Niels Bohr
in the Bohr model of the atom
•Indicates:
• The distance from the nucleus
• The size/volume of the electron’s orbital
• The atom’s major energy levels
•The further the electron is from the
nucleus the greater n will be
n (Principle Quantum #)
The larger the n the
greater volume of the
electron cloud and the
greater the energy
n can be a number
between 1 and 7
l (Orbital Quantum #)
• Indicates the shape of the orbital (the sub
shell)
p
s
d
f
m (Magnetic Quantum #)
The shape is determined by l but m
determines how the shape is oriented in
space.
s orbital – spherical
Only 1 orientation
m (Magnetic Quantum #)
The shape is determined by l but m
determines how the shape is oriented in
space.
p orbital: “dumbbell”
3 orientations
m (Magnetic Quantum #)
The shape is determined by l but m
determines how the shape is oriented in
space.
d orbital:
5 orientations
m (Magnetic Quantum #)
The shape is determined by l but m
determines how the shape is oriented in
space.
f orbital:
7 orientations
m (Magnetic Quantum #)
Each orbital orientation can hold only 2
electrons:
s : 1 orientation = 2 total electrons
p : 3 orientations = 6 total electrons
d : 5 orientations = 10 total electrons
f : 7 orientations = 14 total electrons
s (Spin Quantum Number)
•Indicates which direction the electron
spins
• The 2 electrons in an orbital orientation
will have opposite spins ( + ½ or – ½)
Pauli Exclusion Principle
Each electron in an atom has a
unique set of quantum number
therefore, a maximum of two
electrons can occupy a single
atomic orbital
Electron Configuration
•Quantum numbers are used to write
electron configurations of an element
Hydrogen H
Atomic number: 1
1s1
n
# of electrons
Shape determined
by l
Aufbau Principle
Each electron occupies the lowest
energy orbital available
Two Methods of Writing
Configurations
Method 1
Write the
configuration of Na:
1s2 2s2 2p63s1
Na has 11 electrons
The electrons from
the configuration
should add up to 11.
Remember: s can hold 2 electrons, p 6, d 10 and f 14
Two Methods of Writing
Configurations
Use the periodic table
Always
start at
1s
Ar
Argon’s atomic number is 18
Write the electron
configuration for Ar:
1s2 2s2 2p6 3s2 3p6
The superscripts from the
electron configuration added
equal 18.
Examples
•Write the electron configuration for the following
elements:
C:
1s22s22p2
P:
1s22s22p63s23p3
Ag:
1s22s22p63s23p64s23d104p65s24d9
Rn:
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
Orbital Notation
• Electron configurations can be written
as diagrams
• Orbital Notation diagrams show the
individual orientations and the electrons
that fill them.
•Hund’s Rule: fill orbitals so that the
number of unpaired spins is maximized;
electrons will fill orbitals before pairing
up
Orbital Notation
• Write the orbital notation for Carbon:
Electron configuration: 1s22s22p2
1. Write a line for each orientation associated with a
orbital shape: s = 1, p = 3, d = 5, f = 7
1s
2s
2p
2. Fill electrons in each shape. Place a single electron in
each orbital before pairing them up.
Examples
•Write the orbital notation for the following elements:
C:
P:
Ag:
Rn:
Noble Gas Configuration
All electron configurations can be
abbreviated…
Electron Configuration for Ca is:
Noble gas configuration for Ca is:
Lewis Dot Diagrams
• The outer electrons are use to draw
Lewis Dot Diagrams
•The number of electrons in the highest
principle quantum number (largest “n”
values) determines the number of
electrons in the diagram
Examples
1 electron
H.
Be 1s22s2
2 electrons
Be .
N 1s22s22p3
5 electrons
.N.
Ne 1s22s22p6
8 electrons
: Ne :
.
H 1s1
:
.
:
: