Chapter 5
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Transcript of Chapter 5
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 = ?
m/s 10 x 3.00 c 8
c c
Equation:
c
m1072.8
s110 3.44
sm 1000.3
2
9
8
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
Quantum NumbersName Symbol Definition Details
n
l
m
s
Indicates the orientation in
space (dependent on
the shape)
Subshell indicates the shape of the
orbital
Indicates the average
distance of the electron from the nucleus
Indicates the direction of spin of the electron
n is the period number (a
number between 1 and
7)Shapes are labeled by
letters (s,p,d,f)
s = 1 orientationp = 3 orientationsd = 5 orientationsf = 7 orientationsSpin is either +1/2 or -1/2
Orbital QN
Magnetic QN
Spin QN
Principle QN
If we compared Quantum Numbers to an address then
state
city
street
Side of street
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)
s p
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 electronsd : 5 orientations = 10 total electronsf : 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 PrincipleEach 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 HAtomic number: 1
1s1n
Shape determined by l
# of electrons
Aufbau PrincipleEach electron occupies the
lowest energy orbital available
Two Methods of Writing Configurations
Write the configuration of Na:
1s2 2s2 2p63s1
Na has 11 electrons
The electrons from the configuration should add up to 11.
Method 1
Remember: s can hold 2 electrons, p 6, d 10 and f 14
Two Methods of Writing Configurations
Use the periodic table
Write the electron configuration for Ar:
Ar
Always start at
1s
1s2 2s2 2p6 3s2 3p6
Argon’s atomic number is 18The superscripts from the electron configuration added equal 18.
Examples• Write the electron configuration for the following
elements:
C:
P:
Ag:
Rn:
1s22s22p63s23p3
1s22s22p2
1s22s22p63s23p64s23d104p65s24d9
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
2. Fill electrons in each shape. Place a single electron in each orbital before pairing them up.
1s 2s 2p
Examples• Write the orbital notation for the following
elements:
C:
P:
Ag:
Rn:
Noble Gas ConfigurationAll 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
ExamplesH 1s1
Be 1s22s2
N 1s22s22p3
Ne 1s22s22p6
5 electrons
2 electrons
1 electron
8 electrons
Ne ::
::
H .
N
:
. ..
Be
.
.