Transcript Quantum Mechanics

Energy Level of the Atom
Based on the Bohr
&
The Wave Mechanical Model
The Bohr Model of the Atom
Neils Bohr described an atom with
quantized energy levels. These are discrete
energy levels.
Since we cannot tell both location and
momentum of an electron at the same time
(Heisenberg Principle), this model serves to
predict the probabilities of where the
electrons in an atom are located.
The Wave Mechanical Model
Is used today to describe all atom models.
It was developed by Broglie & Schrodinger
in the 1920’s and replaced the Bohr Model.
 This model describes light as having both
wave and particle properties. This model
was developed based upon the study of
Quantum Physics.
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Quantum Theory
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Describes mathematically the properties of
electrons and small particles.
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This field of study is also known as
Quantum Mechanics.
A Quantum of Energy
Is the minimum amount of energy that can
be gained or lost by an atom.
 When an electron loses or gains energy, it is
always in quantum amounts. These are
always discrete amounts.
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Quantum Numbers
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Are numbers that specify the properties of
atomic orbitals and the properties of
electrons in those orbitals.
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There are a total of FOUR QUANTUM
NUMBERS.
Principal Quantum Number
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Is the first quantum number and is symbolized by
the letter n.
It indicates the main energy level occupied by the
electron.
There are seven prinicipal quantum numbers.
n= 1 through n = 7
The lowest energy level occupied by an atom is n
= 1.
This quantum number describes the amount of
energy the electron possesses.
Ground State & Excited State
of an Atom
The lowest energy level of an electron, n =1,
is also known as the atom’s ground state.
The state of an electron that has a higher
potential energy than the ground state is
called an excited state.
The atom has said to gain one or more
quantums of energy.
Angular Momentum Quantum
Number
The second quantum number is symbolized
by the letter l and indicates the shape of the
orbital path the electrons create.
 Depending on the shape, it is assigned a
letter, s,p, d and f.
 It describes as best as possible the
movement of the electron around the atom.
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Shapes of Orbitals
The s orbitals have a spherical shape left by
the electrons energy signatures.
 The p orbitals have a figure eight shape left
by the electrons energy signatures.
 The d orbitals have a clover shape left by
the electrons energy signatures.
 The f orbitals have
?
shape left by
the electrons energy signatures.
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Magnetic Quantum Number
The third quantum number is symbolized by
the letter m and indicates the orientation of
an orbital around the nucleus.
 It describes the direction the electron is
traveling in 3-dimensional space.
 It takes on an x,y and z vector much like the
direction of N, S, E, and W in 2dimensional space.
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Spin Quantum Number
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The fourth quantum number has no letter to
represent it, but instead has two possible values.
It has a +1/2 or -1/2 spin value and indicates the
fundamental spin states of an electron on its own
axis within an orbital.
Much like the Earth spins on its own axis to give
us night and day while revolving around the sun to
give us our four seasons, the electron in every
atom spins on its own axis, one to the right, the
other to the left in the same orbital as the pair
revolve around the nucleus of an atom.
Orbitals
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Are places in an atom where there is a high
likelihood of finding an electron. (Heisenberg
Priniple)
No more than two electrons can be in any orbital.
The is called the Pauli Exclusion Principle.
There are three possibilities for electrons in an
orbital. The orbitals have 0,1, or 2 electons
contained in them.
This is due to the nature of how an atom fills its
orbitals which will be discussed later.
The Bohr Model of the Atom
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Describes a very tiny dense nucleus (compact)
with a very large diameter where the electrons are
thought to reside (exist) in the various every levels
(distances the electrons exist around the nucleus
based on the amount of energy they contain).
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How the electrons are arranged in these energy
levels dictate the atom’s physical and chemical
properties. *****************************
Electron Configuration
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Is a description of the occupied orbitals in an
atom. Electrons occupy the orbitals in a certain
manner.
In regular electron configurations, atoms fill their
orbitals with electrons from the lower to higher
energy levels.
These types of configurations are true of the main
group elements.
In each energy level, there certain types of
orbitals.
Example of how Atoms fill their
Orbitals
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In the first main energy level, n =1, there is only
one type of orbital that exists.
It is an s orbital with a spherical shape that holds
a maximum of 2 electrons designated 1s2.
The one stands for the Principle Quantum
Number, The s stands for the shape of the orbital
and the 2 signifies the number of electrons in the
orbital.
A perfect example of a 1s2 configuration is
HELIUM.
Continued………….
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In the second Principle Energy Level, n =2, there
are two types of orbitals, an s and p orbital.
The s orbital has a maximum of 2 electrons.
There are 3p orbitals, each with a maximum of 2
electrons in each, making a total of 6 electrons.
For example Neon, which has a total of 10
electrons has configuration of 1s22s22p6.
It has 2 electrons in the s orbital of the first energy
level and 8 electrons in the second energy level, 2
in the s orbital and 2 in each of the 3p orbitals.
Continued……………
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Fluorine has a total of 9 electrons with 2 electrons
in the first energy level and 7 electrons in the
second energy level.
Its configuration would look like this:
1s22s22p5.
In order to learn how to figure the configurations
for the other atoms, we will learn the Wave
Mechanical Model and practice writing the
configurations.
Number of Orbitals
In each energy level, there are that many
sublevels, otherwise known as orbitals with
a total of the following electrons.
 n=1
1s
2e
2e
 n=2
1s,3p
2e, 6e
8e
 n=3
1s,3p,5d
2e, 6e, 10e
18e
n=4
1s,3p,5d, 7f 2e,6e,10e,14e 32e
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Wave Mechanical Model
We use the Wave Mechanical Model below to figure
the electron configurations of each atom.