Name: ____________________
THE BOHR ATOM
In 1913, Niels Bohr (student of Ernest Rutherford) from Denmark
proposed his model of the atom. He agreed with the atom as having a
dense, positively charged nucleus and negatively charged electrons
outside the nucleus. But, he believed these electrons traveled in specific
spherical paths known as orbits.
PRINCIPAL ENERGY LEVEL
Electrons move in principal energy levels or
“shells” around the nucleus.
 principal energy level (“shell”) is a
region of discreet energy levels.
 principal quantum number (n) is the
number of the shell or principal energy
level. For example, when n=2 this refers to
second shell.
the
Each principle energy level (“shell”) can hold a certain amount of electrons, as shown
in the table below.
Principal Energy Levels (n)
n=1
n=2
n=3
n=4
n=5
Maximum # of Electrons (e-)
Write out the ground state electron configuration for the following elements:
Element
7N
17Cl
13Al
Ground State Electron Configuration
Ground State:
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1
Infer: What can you conclude about all the elements on the periodic table
and their electron configurations?
Exited State:
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Photon:
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Nitrogen
Ground State
Electron Configuration
Excited State
Electron Configuration
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Practice: Complete the following table.
Element
Numbe
r of e-
Ground State
electron
configuration
Possible Excited
State electron
configuration
17Cl
13Al
From Ground State to Excited State Back to Ground State
2
He was awarded the Nobel Prize in Physics 1922 "for his services in the investigation
of the structure of atoms and of the radiation emanating from them". During World
War II, Bohr fearing arrest by the Germans, escaped to Britain from where he went to
the US to work on the Manhattan Project at the Los Alamos laboratory in New
Mexico. The Manhattan Project led to the development of the first atom bomb.
Emission Spectrum of Hydrogen
When an electric current is passed through a glass tube that contains hydrogen gas at
low pressure the tube gives off blue light. When this light is passed through a prism
four narrow bands of bright light is observed against a black background.
These narrow bands have the characteristic wavelengths and colors shown in the table
below. If an electron falls from the 3-level to the 2-level, red light is seen.
Wavelength Color
656.2 nm
486.1 nm
434.0 nm
410.0 nm
red
blue-green
blue-violet
violet
Bright-light spectrum:
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3
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How can a bright-line spectrum be
useful in studying stars?
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1. When an excited electron in an atom moves to the ground state, the electron
(1) absorbs energy as it moves to a higher energy state
(2) absorbs energy as it moves to a lower energy state
(3) emits energy as it moves to a higher energy state
(4) emits energy as it moves to a lower energy state
2. Which electron configuration represents the electrons in an atom of Ga in an
excited state?
(1) 2-8-17-3
(2) 2-8-17-4
(3) 2-8-18-3
(4) 2-8-18-4
3. During a flame test, a lithium salt produces a characteristic red flame. This red
color is produced when electrons in excited lithium atoms
(1) are lost by the atoms
(2) are gained by the atoms
(3) return to lower energy states within the atoms
(4) move to higher energy states within the atoms
4. The diagram below represents the bright-line spectra of four elements and a
bright-line spectrum produced by a mixture of three of these elements.
4
Which element is not present in the mixture? (1) A
(2) D
(3) X
(4) Z
5. The bright-line spectrum of an element in the gaseous phase is produced as
(1) protons move from lower energy states to higher energy states
(2) protons move from higher energy states to lower energy states
(3) electrons move from lower energy states to higher energy states
(4) electrons move from higher energy states to lower energy states
Name: __________________________________
The Electron Cloud Model/ Wave Mechanical Model
Heisenberg Uncertainty Principle:
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 SUBLEVELS:
5
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E
N
E
R
G
Y
 ORBITALS:
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Each sublevel has one or more orbitals. The number of orbitals is always the same
regardless of the shell.
s has _____________ orbital
p has _____________ orbitals
d has _____________ orbitals
f has ______________ orbitals
**
Each orbital holds a maximum of 2 electrons.
 ELECTRON PAIR SPIN:
An orbital pair of electrons must have opposite spins. The notation for an
electron pair is ↑↓
SUMMARY
Principal
energy level
“n”
Sublevels orbitals
present
s
present
in
each
p
sublevel
f
Maximum
number of
electrons
d
6
1
2
3
4
5
Hund’s Rule:
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Levels of Representation
I. Electron configuration: This notation shows the number of electrons in each
energy level. Will always be found on the periodic table and represents the ground
state.
Element
Number
of
Electrons
Electron Configuration
17Cl
7N
20Ca
7
II. Representative configuration: Expands the electron configuration to include
principal energy levels, sublevels and number of electrons using the following
notation…
1s22s22p6
Element
Number
of
Electrons
Representative Configuration
17Cl
7N
20Ca
III. Orbital notation: uses up and down arrows to show the electron pairs occupying
each orbital.
Element
17Cl
7N
20Ca
Orbital notation
____
1s
____
2s
____ ____ ____
2p
____
3s
____ ____ ____
3p
____
1s
____
2s
____ ____ ____
2p
____
3s
____ ____ ____
3p
____
____
_____
1s
2s
4s
____ ____ ____
____
____ ____ ____
2p
3s
3p
Question: Look at the calcium representative and orbital configuration. Why aren’t
there any electrons in the 3d sublevel?
IV. Electron dot diagram (Lewis Dot Diagram): Diagrams only the valence electrons
as dots around the element’s symbol that represents the kernel of the atom.
8
Cl
N
Ca
9