Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Chapter 4
4.1 Refinements of the atomic model
Models of the atom so far:
Dalton – atoms are like little “bb’s” - then the _______________ gets discovered
Thomson – atom is like a _______________ “bb”
Rutherford - Gold foil experiment – _______________ “bb”
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-an-atoms.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 fixed 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 light),
wavelength (λ) and frequency (ν).

Wavelength (definition) = ________________________________________________________

Light through prism leads to high energy (violet) low energy (red)

ROYGBIV - colors of the visible spectrum

Bright Line Spectrum (BLS) – caused by e- emitting energy as they ____________ to
_____________________ _________ energy level.

heat sodium - yellow light
2 colors

heat lithium - red light
4 colors

elements can appear to give off the same color light, but each will have its own bls

BLS - used to determine ______________________________

BLS - validates Bohr’s idea that electrons jump to different energy levels and give off different
wavelengths of light
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Light from the sun (white light) appears as a continuous spectrum of light.

Continuous Spectrum of Light (definition) = There are no discrete, individual wavelengths of light
but rather all wavelengths appear, one after the other in a continuous fashion
Spectroscopy (definition) = ____________________________________________________________
Show overhead #6
We will use spectroscopes (____________________________________________________________)
and flame 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
quantized (bls)

Quantized (definition): a specific value (of energy)
Like a set of stairs, the
energy states of an
electron is quantized – i.e.
electrons are only found
on a specific step
The ramp is an example of a
continuous situation in which
any energy state is possible up
the ramp
Bohr’s Energy Absorption Process:


These energy levels are “ quantized “ (the e- cannot be in between levels), the e- disappears from
one shell and reappears in another


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”
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This is an energy
emission process and
what we observe in the
hydrogen line spectrum
“The Excited State”
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms

When energy is added, the electron is found in the “______________________________.”

The Excited State (definition) = ____________________________________________________

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 ground 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 energy, its electrons are promoted to
a higher energy level. When the electron drops back down,
energy is given off in the form of _______________.
2. Each distance fallen back is a specific energy, 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
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 = 2n2 (where n is then shell number)
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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 then abbreviate with nucleus
and numbers on rings
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Short Hand Bohr Model
 Write the symbol of the element
 Use a ) to represent each shell
 Write the # of e- in each shell
Element
Short-Hand e- Configuration
Hydrogen
H )1e-
Lithium
Li )2e- )1e-
Fluorine
F )2e- )7e-
Sodium
Na )2e- )8e- )1e-
At atomic # 19 (z = 19), there is a a break in the pattern. One would expect that energy level #3 would
continue to _______________. However, the next two electrons go into the _______________ energy
level. Look at K and Ca.
Bohr Model illustrations for elements 1-20 on the periodic table examples:
+
IA
VIIIA
H
He
)
+
Li
+
))
+
Na
+
)))
))))
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IIIA
IVA
VA
VIA
VIIA
Be
B
C
N
O
F
))
+
Mg
+
K
+
IIA
)))
))
+
Al
+
)))
))
+
Si
+
)))
))
+
P
+
)))
))
+
S
+
)))
))
Ne
+
Cl
+
)))
))
Ar
+
Ca
+
)
))))
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
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 levels.

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.
In sum, Bohr made 2 huge contributions to the development of modern atom theory

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 quantum mechanical
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 a lie.
Schrödinger (1926) introduced wave mechanics to describe electrons

Based his idea that electrons behaved like _______________

Electrons show diffraction (interference) properties like _______________.

Treats electrons as waves that are found in _______________.

Orbitals (definition) = ____________________________________________________________.
So, the Bohr model
really is
______________________________
There are really many types of orbitals – we can see them on the periodic table
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Draw spdf blocks on blank periodic table
Subatomic Orbitals
Type
# of Sublevels
Total # electrons
Shape
S
Sphere
p
Peanut
d
Dumbbell
f
Flower
Quantum Numbers
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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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
Electron Configuration - a representation of the arrangement of electrons in an atom
 Examples of electron Configuration

1. Li
1s22s1

2. C
1s22s22p6
-Take note that after 4s is filled, 3d is than filled before 4p. This is because 4s has a lower energy than 3d.
-…… 6s than 4f than 5d than 6p
-When writing out the electron configuration, always write your numbers in numerical order
-

Y 1s22s22p63s23p64s23d104p65s24d1 – NO!

Y 1s22s22p63s23p63d104s24p64d15s2
Note: 3d has a few exceptions exceptions
o
Cr is 4s1 3d5 and Cu is 4s1 3d10 - students should be able to identify these
elements simply based on how many electrons they have.
Examples:
Be
O
Ca
Mn
Pb
Os
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
We can also do shorthand electron configuration. Use previous row’s noble gas in brackets, then present
the electron configuration for the current row.
Be
Na
Si
Orbital notation is another way to represent electron arrangement in atoms.
Electrons enter orbitals in a set pattern. For the most part, they follow these rules:
1. The Aufbau Principle - electrons must fill lower energy levels before entering _____________.
Draw energy level diagram here:
Draw diagonal diagram here:
Orbitals are like "rooms" within which electrons "reside".
The s subshell has one s-orbital. The p subshell has three p-orbitals.
Each orbital can hold at most 2 electrons
See a good online illustration at http://www.avogadro.co.uk/light/aufbau/aufbau.htm
2. Hund’s Rule (better known as the _____________)
Before any second electron can be placed in a sub level, all the orbitals of that sub level must contain at
least one electron – spread out the e- before pairing them up.
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
3. Pauli Exclusion Principle - electrons occupying the same orbital __________________________.
Examples:
Li
F
Na
Sc
We can also do shorthand orbital notation (outer shell only)
Ca
N
Fe
Significance of electron configurations
Valence shell electrons - ____________________________________________________
no atom has more than ______________________
Noble gases - 8 valence electrons - _______________ reactive of all elements
Lewis Dot structures: NSEW (cheating) also show correct way, count to 8
Lewis Dot Structures
Exception – He
Try Lewis Dot structures for additional elements here:
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Accelerated Chemistry
Chapter 4 Notes – Arrangement of Electrons in Atoms
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