Transcript Unit 4 Electronic Structure of Atoms

14 November 2011


Objective: You will be able to:
 describe evidence for the current theory
of the electronic structure of atoms.
Homework: p. 312 #3, 4, 5, 6, 7, 9, 16,
19, 25, 32
Electronic Structure of Atoms
Next Units:
Electron configuration
 Trends on the periodic table
 Ionic/covalent bonding
 Chemical reactivity

In order to understand these things

we’ll study the electronic structure of
atoms
The Wave Nature of Light
electromagnetic radiation (a.k.a.
light) is a form of energy with wave and
particle characteristics. It moves through
a vacuum at the speed of light
 speed of light: 3.00x108 m/s

To describe waves…


wavelength (λ lamda): the distance
between two adjacent peaks of a wave
frequency (v): the number of wavelengths
that pass a given point in a second
Electromagnetic Spectrum
electromagnetic spectrum includes all
wavelengths of radiant energy
 visible spectrum: the part of the
electromagnetic spectrum that is visible to
the human eye (wavelengths between 400
and 700 nm)

Quantized Energy and Photons
quantum (a.k.a. photon) is a specific
particle of light energy that can be emitted
or absorbed as electromagnetic radiation.
 Energy of a photon E=hv
 Energy is quantized – matter is allowed
to emit or absorb energy in discrete
amounts, whole number multiples of hv.

How are these things related to
electromagnetic radiation?
v=c/λ
E=hv
λ = wavelength in nm
v = frequency in 1/s or
hertz
1 Hz = 1/s
c = speed of light =
3.00x108 m/s
= 3.00x1017 nm/s
1 nm = 10-9 m
E = energy of a single
photon in Joules
h = Planck’s constant =
6.63x10-34 J s
E=hc/λ
Example 1
Calculate the energy (in joules) of
4
a. a photon with a wavelength of 5.00x10
nm (infrared region)
b. a photon with a wavelength of 5.00x10-2
nm (x-ray region)
Example 2
What is the frequency and the energy of a
single photon?
 What is the energy of a mole of photons of
light having a wavelength of 555 nm?

Problem

The energy of a photon is 5.87x10-20 J.
What is its wavelength, in nanometers?
Homework
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p. 312 #3, 4, 5, 6, 7, 9, 16, 19, 25, 32
15 November 2011
Take Out Homework
 Objective: You will be able to:
 describe and explain experimental
evidence for energy levels
 Homework Quiz: The energy of a photon
is 3.98x10-19 J. What color light do you
observe?

Agenda
Homework Quiz
II. Hand back tests
III. Line spectra and the Bohr model of the
atom
Homework: p. 313 #23, 24, 25, 26, 30, 31,
35, 36
I.
Line Spectra and the Bohr Model
atomic emission spectrum (a.k.a. line
spectrum): a pattern of discrete lines of
different wavelengths that result when the
light energy emitted from energized atoms
is passed through a prism
 Each element produces a characteristic or
identifiable pattern

Demo
Emission spectra of common cations
 Note: we don’t have a way to separate all
the wavelengths of light into discrete lines
of color, so we’re just seeing all those lines
of color blended together.
 http://www.youtube.com/watch?v=2ZlhR
Chr_Bw&feature=related

So, why do we see these discrete
lines of color?
Bohr model of the atom: energies are
quantized. Electrons move in circular,
fixed energy orbits around the nucleus.
 Usually, electrons are in the most stable
“ground” state.
 When energy (a photon) is added, they
“jump” up to the “excited” state
 They fall back down, and release that
photon.

Multimedia
http://www.youtube.com/watch?v=45KG
S1Ro-sc
 http://www.colorado.edu/physics/2000/
quantumzone/lines2.html
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Homework

p. 313 #23, 24, 25, 26, 30, 31, 35, 36
16 November 2011

Objective: You will be able to:
 explain how line spectra give evidence
for the existence of energy levels
 explain how quantum mechanics
describes electron configuration
Agenda
Homework Quiz
II. Go over homework
III. How do atoms emit photons?
IV. Quantum mechanics: how do we
describe where the electrons are?!
V. Writing orbital notation and electron
configuration
Homework: p. 313 #23-26, 30, 35, 48, 53,
60, 63,
I.
Energy levels
Wave Behavior of Matter
Like light, electrons have characteristics of
both waves and particles. Because a wave
extends into space, its location is not
precisely defined.
 uncertainty principle: it is impossible to
simultaneously determine the exact
position and momentum of an electron.
 we can only determine the probability of
finding an electron in a certain region of
space.

Quantum Mechanics and Atomic
Orbitals
quantum mechanical model:
mathematical model that incorporates
both the wave and particle characteristics
of electrons in atoms.
 quantum numbers: describe properties
of electrons and orbitals
 each electron has a series of four
quantum numbers

Table of Quantum Numbers
Table of quantum numbers and
orbital designations
Pauli Exclusion Principle

Two electrons in an atom can’t have the
same four quantum numbers
 Two electrons per orbital, with opposite
spins
Representations of Orbitals

orbital: calculated probability of finding
an electron of a given energy in a region of
space
p orbitals
d orbitals

orbital ≠ orbit
17 November 2011
Objective: You will be able to:
 write the orbital and electron
configuration for any element
 describe several exceptions to the orbital
filling rules
 Homework Quiz: Describe, as completely
as you can in a paragraph or two, the
evidence that convinced Neils Bohr of the
existence of energy levels instead of a cloud
of electrons.

Agenda
Homework Quiz
II. Go over homework
III. Electron configuration notation
IV. Problem Set
Unit 4 Quiz Weds.
I.
Atoms with more than one electron
like hydrogen
 electron-electron repulsions cause
different sublevels to have different
energies

Order those orbitals fill
Electron Configuration

distribution of electrons among various
orbitals of an atom
Rules for Writing E- Config.
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1.
2.
3.
4.
at the ground state
Fill the lowest energy level first. Electrons in
the same orbital must have opposite spins.
Total number of electrons = atomic number
Only two electrons per orbital!
Do not pair electrons in a orbitals of the same
energy until each orbital has one electron of
the same spin (Hund’s rule)
Label each sublevel with the energy level
number and letter of the sublevel
Examples
1.
2.
3.
phosphorus
calcium
iron
Paired-ness of Electrons
Paramagnetic: an atom having one or
more unpaired electrons
 Ex: Li, B, C…
 Diamagnetic: all electrons in an atom are
paired.
 Ex:

Excited-State Configuration
has a higher energy than the ground-state
electron configuration.
 One or more electrons occupy higher
energy levels than predicted by the rules
 Ex: Iron in an excited state:

Electron Configuration and the
Periodic Table

Elements with similar electron
configurations arranged in columns
Examples
1.
2.
Write the electron configuration for
palladium
Write the electron configuration for
osmium
Condensed Electron Config.
shows only the electrons occupying the
outermost sublevels
 preceded by the symbol for the noble gas
in the row above the element
 Example: calcium
 Example: iodine

Unusual Electron Configs.
Cr and Mo: ground state valence
electrons are arranged s1d5 rather than
s2d4
 a half filled d orbital is more stable than a
more-than-half-filled d orbital
 Cu, Ag and Au have s1d10 ground state
configs because of the stability of a fill d
orbital
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21 November 2011

Objective: You will be able to:
 describe the electronic structure of an
atom and make associated calculations.
Agenda
Math with exponents (#6)
II. Problem set work time
Homework: Problem set due tomorrow
Quiz Mon. on all electronic structure,
calculations, evidence for Bohr’s theory…
I.
28 November 2011
Objective: You will be able to:
 show what you know about the
electronic structure of atoms on a quiz
 You need:
 periodic table
 calculator
 pen/pencil

You have only one period
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Work smart: Go through the MC and answer the
ones you can easily answer.
Then, go through and spend more time on the
difficult ones.
Only write the noble gas notation if you need
electron configuration to answer a question.
Only do the orbital notation of the parts you
really need to “see.”
Don’t spend a long time on any one question
until you’ve tried every problem on the quiz.
Pay attention to UNITS.