Download Chapter 11 Atoms, Energy and Electron Configurations

Chapter 11
Atoms, Energy and Electron Configurations
Objectives
1.  To review Rutherford’s model of the atom
2.  To explore the nature of electromagnetic radiation
3.  To see how atoms emit light
Chapter 11
Atoms, Energy and Electron Configurations
A. Rutherford’s Atom
…….but
there is a
problem
here!!
Chapter 11
Atoms, Energy and Electron Configurations
Using Rutherford’s Model Atoms Should Collapse….
…..then how
are they so
stable?
Chapter 11
Atoms, Energy and Electron Configurations
When were you last exposed to
electromagnetic radiation?
Chapter 11
Atoms, Energy and Electron Configurations
B. Energy and Light
•  What is the nature of electromagnetic radiation?
•  How are the types of electromagnetic radiation different?
–  Light can be modeled as a wave, like a wave
in water
Chapter 11
Atoms, Energy and Electron Configurations
B. Energy and Light
•  How are the types of light different?
(m)
ν(
s-1)
c = ν.λ –  Wavelength, λ (Greek letter “lambda”) units - m
–  Frequency, ν (Greek letter “nu”) units - s-1 or Hertz (Hz)
–  Amplitude, peak height – relates to energy in wave
–  Speed, c : velocity of light in a vacuum is 3x108 m.s-1
Chapter 11
Atoms, Energy and Electron Configurations
B. Energy and Light
•  Electromagnetic radiation
Chapter 11
Atoms, Energy and Electron Configurations
Wavelength and Frequency of Visible Light
Frequency in Terahertz (1THz = 1012 Hz) and
Wavelength in Nanometers (1nm = 10-9 meters)
Chapter 11
Atoms, Energy and Electron Configurations
Light Sometimes Behaves in Un-wavelike Ways
•  The Photoelectric Effect
–  Light shining on a metal surface can cause electrons to be
separated from their atoms
–  Below a threshold frequency no electrons are emitted however
high the intensity
–  At the threshold frequency electrons start to be emitted
–  At higher frequencies
electrons have additional
kinetic energy
Photoelectric Effect Demo
Chapter 11
Atoms, Energy and Electron Configurations
B. Energy and Light
•  Dual nature of light – Two co-existing models
–  Wave
–  Photon – packet of energy
Chapter 11
Atoms, Energy and Electron Configurations
B. Energy and Light
•  Different photons (from light of different wavelengths) carry
different amounts of energy.
Energy of photon = h.ν (h is Planck’s Constant )
Chapter 11
Atoms, Energy and Electron Configurations
C. Emission of Energy by Atoms
•  Atoms can give off light
–  They first must receive energy and become excited.
–  The energy is released in the form of a photon.
Chapter 11
Atoms, Energy and Electron Configurations
Typical Colors From Flame Tests
K+
Na+
Periodic Table of
Fireworks
Li+
Which flame
represents a
higher energy
transition?
Cu2+
Chapter 11
Atoms, Energy and Electron Configurations
Objectives
1.  To understand how the emission spectrum of
hydrogen demonstrates the quantized nature of
energy
2.  To learn about Bohr’s model of the hydrogen atom
3.  To understand how the electron’s position is
represented in the wave mechanical model
Chapter 11
Atoms, Energy and Electron Configurations
A. The Energy Levels of Hydrogen
•  Only certain types of photons are produced when excited
Hydrogen atoms release energy. Why?
Chapter 11
Atoms, Energy and Electron Configurations
A. The Energy Levels of Hydrogen
•  Atomic states
–  Excited state – atom
with excess energy
–  Ground state – atom in
the lowest possible
state
•  When an H atom absorbs
energy from an outside
source it enters an excited
state.
Chapter 11
Atoms, Energy and Electron Configurations
A. The Energy Levels of Hydrogen
•  Energy level diagram
•  Energy in the photon corresponds to the energy used
by the atom to get to the excited state.
Chapter 11
Atoms, Energy and Electron Configurations
A. The Energy Levels of Hydrogen
•  Only certain types of photons are produced when H atoms
release energy. Why?
Chapter 11
Atoms, Energy and Electron Configurations
A. The Energy Levels of Hydrogen
•  Quantized Energy Levels
–  Since only certain energy changes occur the H atom
must contain discrete energy levels.
Chapter 11
Atoms, Energy and Electron Configurations
B. The Niels Bohr Model of the Atom (1913-1915)
•  Bohr’s model of the atom
–  Quantized energy levels
–  Electron moves in a circular orbit
–  Electrons jump between levels by absorbing or
emitting photons of a particular wavelength
Able to mathematically
explain the emission
spectrum of Hydrogen
(compare with Rutherford)
Chapter 11
Atoms, Energy and Electron Configurations
B. The Bohr Model of the Atom
•  Bohr’s model of the atom was not totally correct.
–  Had difficulties with spectra of larger atoms
–  Electrons do not move in a circular orbit and don’t
seem to behave like discrete particles all the time
Maybe small particles, such as electrons,
can also behave like waves having a dual
nature (just like photons)……?
Chapter 11
Atoms, Energy and Electron Configurations
C. The Wave Mechanical Model of the Atom (de Broglie
and Schroedinger – mid-1920’s)
•  Orbitals
–  Nothing like orbits
–  Probability of finding the electron within a certain space
BohrSchrodinger
Chapter 11
Atoms, Energy and Electron Configurations
Objectives
1.  To learn about the shapes of the s, p and d orbitals
2.  To review the energy levels and orbitals of the wave
mechanical model of the atom
3.  To learn about electron spin
Chapter 11
Atoms, Energy and Electron Configurations
A. The Hydrogen Orbitals
•  Orbitals do not have sharp boundaries.
90% boundary
Chapter 11
Atoms, Energy and Electron Configurations
A. The Hydrogen Orbitals
Hydrogen Energy Levels
•  Hydrogen has discrete energy
levels.
•  Called principal energy
levels (electron shells)
•  Labeled with whole numbers
•  Energy is related to 1/n2
•  En = E1/n2
•  Energy levels are closer
together the further they are
from the nucleus
Chapter 11
Atoms, Energy and Electron Configurations
A. The Hydrogen Orbitals
Hydrogen Energy Levels
•  Each principal energy level is divided into sublevels.
–  Labeled with numbers and letters
–  Indicate the shape of the orbital
Chapter 11
Atoms, Energy and Electron Configurations
Orbital Designations
Chapter 11
Atoms, Energy and Electron Configurations
Orbitals Define the Periodic Table
“Orbitals” are
“Energy Levels”
Chapter 11
Atoms, Energy and Electron Configurations
A. The Hydrogen Orbitals
Hydrogen Energy Levels
•  The s and p types of sublevel
Chapter 11
Atoms, Energy and Electron Configurations
Representation of s, p, d atomic orbitals
Chapter 11
Atoms, Energy and Electron Configurations
A. The Hydrogen Orbitals
Hydrogen Orbitals
•  Why does an H atom have so many orbitals and only 1
electron?
–  An orbital is a potential space for an electron.
–  Atoms can have many potential orbitals.
•  s, p, d, f orbitals named for sharp, principal, diffuse and
fundamental lines on spectra. Further orbitals designated
alphabetically
Chapter 11
Atoms, Energy and Electron Configurations
s
p
d
d
Orbitals
f
f
f
g
g
g
g
Chapter 11
Atoms, Energy and Electron Configurations
B. The Wave Mechanical Model: Further Development
Electron Spin
•  Close examination of spectra revealed doublets
•  Need one more property to determine how electrons
are arranged
•  Spin – electron modeled as a spinning like a top
•  Spin is the basis of magnetism
Chapter 11
Atoms, Energy and Electron Configurations
B. The Wave Mechanical Model: Further Development
Pauli Exclusion Principle
•  Pauli Exclusion Principle (Wolfgang Pauli 1925) - an
atomic orbital can hold a maximum of 2 electrons and
those 2 electrons must have opposite spins
•  When an orbital contains two electrons (of opposite
spin) it is said to be full
What are the four descriptors that define an energy
level / electron’s position in an atom?
Chapter 11
Atoms, Energy and Electron Configurations
Objectives
1.  To understand how the principal energy levels fill with
electrons in atoms beyond hydrogen
2.  To learn about valence electrons and core electrons
3.  To learn about the electron configurations of atoms
4.  To understand the general trends in properties in the
periodic table
Chapter 11
Atoms, Energy and Electron Configurations
A. Electron Arrangements in the First 18 Atoms on the
Periodic Table
•  H atom
–  Electron configuration – electron arrangement – 1s1
–  Orbital diagram – orbital is represented as a box with a
designation according to its sublevel. Contains arrow(s)
to represent electrons (spin)
Chapter 11
Atoms, Energy and Electron Configurations
A. Electron Arrangements in the First 18 Atoms on the
Periodic Table
•  He atom
–  Electron configuration – 1s2
–  Orbital diagram
Chapter 11
Atoms, Energy and Electron Configurations
A. Electron Arrangements in the First 18 Atoms on the
Periodic Table
•  Li atom
–  Electron configuration– 1s2 2s1
–  Orbital diagram
Write the electron configuration
and orbital diagrams for Boron,
Nitrogen, Fluorine and Argon
Chapter 11
Atoms, Energy and Electron Configurations
A. Electron Arrangements in the First 18 Atoms on the
Periodic Table
Write the full electron configuration of Neon and Sulfur
Draw an orbital diagram for Magnesium and Chlorine
Chapter 11
Atoms, Energy and Electron Configurations
Order of Filling of Orbitals
Atoms fill their orbitals in
the order of their energies:
Chapter 11
Atoms, Energy and Electron Configurations
B. Electron Configurations and the Periodic Table
•  Orbital filling and the periodic table
Dynamic
Periodic Table
PT 2a
PT 2b
Chapter 11
Atoms, Energy and Electron Configurations
B. Electron Configurations and the Periodic Table
•  Electron configurations for K through Kr
Chapter 11
Atoms, Energy and Electron Configurations
B. Electron Configurations and the Periodic Table
If there were more elements……….
Chapter 11
Atoms, Energy and Electron Configurations
A. Electron Arrangements in the First 18 Atoms on the
Periodic Table
Classifying Electrons
•  Valence electrons – electrons in the outermost (highest)
principal energy level of an atom
•  Core electrons – inner electrons
•  Elements with the same valence electron arrangement
(same group) show very similar chemical behavior.
Chapter 11
Atoms, Energy and Electron Configurations
B. Electron Configurations and the Periodic Table
Chapter 11
Atoms, Energy and Electron Configurations
Using a Noble Gas Shorthand
•  We can abbreviate electron configurations by using the
configuration of the previous noble gas to cover the first
part of the list of orbitals
•  Mg is 1s2 2s2 2p6 3s2 or [Ne] 3s2
•  The noble gas portion is the equivalent to the group of
core electrons
•  Use the Noble Gas shorthand to show the electron
configurations of Carbon, Chlorine and Zirconium
Chapter 11
Atoms, Energy and Electron Configurations
C. Atomic Properties and the Periodic Table
Metals and Nonmetals
•  Metals tend to lose electrons to form positive ions.
•  Nonmetals tend to gain electrons to form negative ions.
Chapter 11
Atoms, Energy and Electron Configurations
C. Atomic Properties and the Periodic Table
Atomic Size
•  Size tends to increase down a column.
•  Size tends to decrease across a row.
Effects of
Shielding of
outer electrons
by inner orbitals
(close to scale)
Larger
Chapter 11
Atoms, Energy and Electron Configurations
C. Atomic Properties and the Periodic Table
Ionization Energies
•  Ionization Energy – energy (ΔH) required to remove an
electron from an individual atom (gas)
–  Tends to decrease down a column
–  Tends to increase across a row
–  Changes in an opposite direction to atomic size
Chapter 11
Atoms, Energy and Electron Configurations
Ionization Energies
Chapter 11
Atoms, Energy and Electron Configurations
Electron Affinity
•  Electron Affinity is
defined as ΔH for the
process:
X(g) + e- = X(g)ΔH = Electron Affinity
Larger
Chapter 11
Atoms, Energy and Electron Configurations
Electronegativity
•  Ionization Energy and
Electron Affinity are
combined to give
Electronegativity – a
measure of how well
atoms compete for
electrons in a bond
Larger