Download Accelerated Chemistry Chapter 4 Student Notes

Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Chapter 4 problem set:
Page 124 Chapter Review: 8, 9, 16, 17, 18, 20, 22, 27, 28, 30, 33, 36, 37
4.1 Refinements of the atomic model
Models of the atom so far:
Dalton – atoms are like little “bb’s” - then the
Thomson – atom is like a
“bb”
Rutherford - Gold foil experiment –
-
gets discovered
“bb”
1909 - Gold Foil Experiment (Rutherford - New Zealand)
- The Experiment:
towards a thin sheet of
seen on the
particles from
(in the lead box) were released
foil. Most of the particles went through and were
screen.
alpha particles bounced back.
- Concluded: 1 –
2–
3–
4–
-
Analogy: if an atom is the size of the Eagle’s stadium, then the nucleus is the
size of a tennis ball floating in the middle of the stadium.
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Bohr model of the atom (1913) – Neils Bohr – Danish Physicist
The Bohr model of the atom comes from the idea that light
is
View vision learning example of hydrogen and helium atoms.
http://web.visionlearning.com/custom/chemistry/animations/CHE1.2-anatoms.shtml
The Bohr Atom (1913)
In 1913, Neils Bohr, a Danish
physicist proposed:

All the positive charge was in
the

Electrons orbited the nucleus
much like planets orbit the
sun (at
distances)

The
the electrons to the
nucleus, the
energy it
has.

The
the electron is
from the nucleus, the
energy it has.
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
The Electromagnetic Spectrum - Defined

Visible light, x-rays, ultraviolet radiation, infrared radiation,
microwaves and radio waves are all part of the electromagnetic
spectrum

The spectrum consists of electromagnetic radiation –

Waves can be described by the wave equation which includes
velocity (c = speed of
),
(λ) and
(ν).

Wavelength (definition) =

Light through prism leads to high energy (violet) low energy (red)
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms

ROYGBIV - colors of the

bright line spectrum (bls) - frequencies of light give off by certain
substances when
is added to them.

heat sodium - yellow light

heat lithium - red light

elements can appear to give off the same color light, but each will
have its own

bls - used to determine

bls - validates Bohr’s idea that electrons
levels and give off different wavelengths of
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spectrum
to different energy
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Light from the sun (white light) appears as a
of light.

spectrum
Continuous Spectrum of Light (definition) = There are
discrete,
individual wavelengths of light but rather
wavelengths appear,
one after the other in a continuous fashion
Spectroscopy (definition) =
_
.
Show overhead #6
We will use spectroscopes (
) and
tests to study elements because
each element emits a different spectrum of light when exited .
Bohr proposed that the energy possessed by an e- in a H-atom and
the radius of the orbit are
(bls)

Quantized (definition): a specific value (of energy)
The ramp is an example of a
continuous situation in which
any energy state is possible up
the ramp
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Like a set of stairs, the
energy states of an
electron is quantized – i.e.
electrons are only found
on a specific step
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Bohr’s Energy Absorption Process:

Light or energy excites an e- from a lower energy level (e- shell) to a
___________energy level

These energy levels are “
“ (the e- cannot be in
between levels), the e- disappears from one shell and reappears in
another

This absorption or excitation process is called a
or
_________________

Ground State Analogy = a spring and two balls
Both the atom and e- now
have higher energy
The e- absorbs energy in the
ground state and is excited
to a higher level
“The Ground State”
This is an energy
emission process and
what we observe in the
hydrogen line spectrum
“The Excited State”
State”

When energy is added, the electron is found in the “

The Excited State (definition) =
.”
_________________
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms

An illustration of Bohr’s Hydrogen atom (from ground to excited
state):
 The atomic line spectral lines - when an e- in an excited state decays
back to the
state
The electron loses
energy, light (colors)
is emitted and the ereturns to the
ground state
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
The Bohr Model - Summary
1. When an atom absorbs
, its
electrons are
to a higher
energy level. When the electron
_________, energy is given off in the form
of
.
2. Each distance fallen back is a specific
________, and therefore, a specific
.
3. Since electrons can fall from level 5 to 4, 5
to 3, etc.,
.
Click for animated H-atom:
Bohr's Atom: Quantum Behavior in Hydrogen
http://www.visionlearning.com/library/module
_viewer.php?mid=51&l=15
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Bohr also predicted that since electrons would occupy specific
energy levels and each level holds a specific number of electrons

The maximum capacity of the first (or innermost) electron shell is

Any element with more than two e-, the extra e- reside in additional
_________________.
Group IA
VIA
VIIA
VIIIA
Lithium
Oxygen
Fluorine
Neon
Sodium
Electron Configurations for Selected
Elements

The number of e- per shell =

Animated Example, Atomic structure animation table -
(where n is then
number)
http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-anatoms.shtml
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.
Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Draw Bohr Models for the elements with atomic numbers 1-10 below
H
He
Li
Be
B
C
N
O
F
Ne
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Bohr Model illustrations for elements 1-20 on the periodic table
examples:
IA
VIIIA
H
He
IIA
IIIA
IVA
VA
VIA
VIIA
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
So, there is a relationship between the main column # and the number of
outershell electrons.

Column # = the number of
electrons
And, there is a relationship between the row # and the number of energy
.

Row # = the number of
The Bohr model truly works well for the H atom only – for elements larger
than H the model does not work.
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
In sum, Bohr made 2
modern atom theory
contributions to the development of

He explained the atomic line spectra in terms of

He introduced the idea of quantized electron
in the atom
The Bohr atom lasted for about 13 years and was quickly replaced by
the
model of the atom. The Bohr model is a
good starting point for understanding the quantum mechanical model
of the atom
Do Ch4 worksheet #1 – question #1
4.2 Quantum numbers and atomic orbitals & 4.3
Electron Configuration
The Bohr model describes the atom as having definite orbitals occupied by
___________________________.
As with all chemistry, we soon learn that the Bohr model is not correct.
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Schrödinger (1926) introduced wave mechanics to describe electrons

Based his idea that electrons behaved like

Electrons show diffraction (
.

Treats electrons as waves that are found in
o
) properties like
.
Charge Cloud Model
In the 1930’s - 1940’s more work leads to the charge cloud model which
is also known as the quantum mechanical model. This model does not
show the path of

- just the most
location.
Orbitals (definition) =
.
Orbitals are like "rooms" within which electrons "reside".
The s subshell has ___ s-orbital. The p subshell has ____ p-orbitals.
Each orbital can hold at most
electrons
See a good online illustration at
http://www.avogadro.co.uk/light/aufbau/aufbau.htm
So, the Bohr model really is the
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
There are many types of orbitals – we can see them on the periodic table
Sublevel
# of orbitals
e- per orbital
Max # of e- per
sublevel
Shape of orbital
s
p
d
5
dxy, dyz, dxz,
dx2 – y2, dz2
f
7
(too complicated)
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
- energy levels, sublevels, and total number of electrons per shell
Energy Level (shell)
Sublevel(s) and Electrons
Total # of Electrons per Shell
1
2
3
4
5
6
7
Show transparency of orbitals in each energy level
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Bohr Model Examples (1 to 20):
H
Li
N
K
He
Be
B
C
N
O
F
Ne
Mg
Al
Si
P
S
Cl
Ar
Ca
EC for higher atomic #’s
At atomic # 19 (z = 19), a break in the pattern ensues. One would expect that the
orbital to fill after 3p would be 3 d, but alas, it is not. 4s is the next level we fill
as it has lower energy than 3d. Look at potassium and calcium.
Do Construction of Periodic Table Activity
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Electron configurations
- Electrons enter orbitals in a
pattern. For the most part, they follow these rules:
Aufbau principle - electrons must fill
energy levels before entering
higher level.
examples (do Bohr models and electron configurations):
Element
Bohr Model
Electron Configuration
Oxygen
Potassium
Copper
Silver
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Draw diagonal diagram here:
1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10 5f14
6s2 6p6 6d10
7s2 7p6
-
Kernal Electrons:
shell electrons
-
Valence Electrons:
shell electrons
Pauli Exclusion principle - electrons occupying the same orbital must have
spin.
electron spin - clockwise or counterclockwise
Pauli exclusion principle - 2 electrons in the same orbital must have
Hund’s rule ( better known as the Stinky Bus Rule) - before any second
electron can be placed in a sub level, all the orbitals of that sub level must
contain at least
electron.
Orbital notation is another way to represent
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arrangement in atoms.
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spins.
Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Examples: Bohr Model, Electron Configuration, and Orbital Notation:
Element
Bohr Model
Electron Configuration
Orbital Notation
Argon
1s
2s
2p
3s
3p
1s
2s
2p
3s
3p
Manganese
4s
3d
- example Iodine (Bohr model, electron configuration, orbits, and orbital
notation:
5p
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
- Exceptions to the Aufbau Principle
- Cr is ________________
not
4s2 3d4
- Other exceptions:
-
students should be able to identify these elements simply based on
how many electrons they have.
Do the orbital notation for Copper:
Significance of electron configurations
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Valence shell electrons -
-
for n = 5, pattern is very complicated valence electrons
-
Noble gases -
-
kernel - part of the atom
the nucleus)
-
example - sodium kernel =
valence electrons -
electrons involved with bonding
no atom has more than
reactive of all elements
of valence electrons (includes
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
-
Element
examples (find the outershell electron configuration, shorthand
notation, and Lewis dot diagram –
Outershell Electron
Configuration
Shorthand Notation
Lewis Dot Diagram
Oxygen
Chlorine
Iron
Cobalt
Potassium
Strontium
Silver
K+1
O-2
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Quantum numbers show the “addresses” of electrons – each electron
has 4 different quantum numbers:
1. principle (n):
2. azimuthal (l):
3. magnetic –
4. spin -
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