Transcript Modern Model of the Atom

Modern Model of the Atom
From Bohr to Today
Note to Reader
• Words in bright pink are notes from the teacher
to help you understand the material. IF you are
writing this down instead of printing it, these do
not need to be copied.
Neils Bohr’s Model
• The electrons must be in a fixed orbit around the
nucleus.
• Each orbital has its own specific energy level.
• No electrons can exist in between the energy
levels.
• But remember, this only worked for Hydrogen.
Heisenberg and Schrodinger
• Realized that electrons are not completely
described as small particles but that they can
have both wave and particle properties.
• This means that electrons were behaving a little
like light and a little like matter.
Heisenberg’s Uncertainty Principle
• On the scale of atomic particles, we cannot
determine exactly the position, direction of
motion, and speed all at the same time.
• Also restated as “The behavior of particle is
affected by the act of observing the particle.
Therefore, by observing it you have changed
something about it.”
Schrodinger
• Determined an equation to
give the probability of finding
an electron in a given area,
which he named ‘Orbitals.’
• These orbitals provide the
electron density distributed
about the nucleus.
• Orbitals are described by
quantum numbers.
Quantum Mechanical Model
• Does not describe the movement of
the electrons, only where they are
most likely found any point in time.
• Orbital – a region in which an
electron will have the greatest
probability of being found. (Any
orbital can hold two electrons.)
Quantum Numbers
• Set of 4 numbers describes everything you need
to know to find an electron within a specific
atom. (Tells its address.)
For Example
• In order to tell someone where you live, you
need to give them four pieces of information.
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▫
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What state you live in
What city you live in
What street you live on
What the house number is
• Without all four pieces of information, the
person will not be guaranteed to find your
house. It is the same with an electron… we need
to be given four pieces of information to find it.
Principle quantum number (N)
• Tells the distance from the nucleus; the main
energy level (Like the state in your address)
• Numbers 1-7
(shell 1 is close to the nucleus and shell 7 is far)
• Corresponds to rows on the periodic table and
the rings in Bohr’s model.
Principle
Energy Level
1
2
3
4
5
6
7
So…
• Hydrogen has one electron in principle energy
level 1.
• Calcium has 20 electrons.
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2 are in PE 1
8 are in PE 2
8 are in PE 3
2 are in PE 4
1
1 2
1 2
1 2
2
3 4 5 6 7 8
3 4 5 6 7 8
Orbital Quantum Number (l)
• Tells the shape of the orbit.
• (Like the city in your address).
• As you move up principle energy levels, you can
add one more type of orbit.
• (Kind of like if you have a small city, it doesn’t
have many restaurants, but the larger it gets, the
more kinds it will have.)
Orbital Quantum Number
• S shape – 1 in every principle energy level, holding 2 electrons
each
• P shape – 3 total in every PE level starting with level 2
(Each level will have one of each “version” below. Remember,
each of the orbits holds 2 electrons, so the p shape holds a total of
6 electrons in any principle energy level)
Orbital Shapes Continued
• d – 5 total in every PE starting with level 3
(5 orbits with 2 electrons each = 10 electrons)
4 of this type
1 of this type
• f – 7 total in every PE starting with level 4
(the pictures get very complicated here, you don’t
need to know what an f orbital looks like)
Finding Orbital Quantum #s on the Periodic Table
P Block
S Block
D Block
F Block
Magnetic Quantum Number
• Tells the position in space.
• (Like the street name in your address).
• Since there are three different versions of p
orbits, this tells us which version we are talking
about. Is it the one that is oriented on the x axis,
the y axis or the z axis. (We will not be
designating these with actual numbers this
year.)
Spin Quantum Number
• Tells the direction of spin of the electron.
• (Like the house number in your address.)
• Pauli Exclusion Principle: No two electrons can
have the same of Quantum Numbers.
• For the two electrons that exist in the same principle
energy level, in the same shape, in the same
orientation, the two electrons spin in opposite
directions.
• If you live in the same state, city and street as your
friend, you have to have different house numbers to
tell them apart.