The Quantum Model of the Atom

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The Quantum Model of the Atom

• Mrs. Johnson

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de Broglie

• Light behaves as both a wave and a particle
• So do e ( they are particles, but also have wave
  like properties because they can be bent, or
  diffracted)

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Bohr vs. the Quantum Model

• In each energy level, a certain amount of
  electrons can fit
• 2n2
• When n1, there are 2 electrons
• When n2, there are 8 electrons
• When n3, there are 18 electrons
• When n4, there are 32 electrons

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Electrons

• Electrons do not travel around the nucleus in
  neat orbits, said by Bohr
• They exist in certain regions called orbitals
• Orbital-3 dimensional region around the nucleus
  that indicates the probable location of an e
• Energy of e are higher when further from nucleus

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Uncertainty Principle

• Can confine an e to a specific energy level
  (quanta) or region of an atom
• It mathematically isolates an e to a specific
  orbital, but cannot tell its exact position
• Schrodingers equation allows physicists to find
  the probable location of an e

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Quantum Numbers

• Specify the properties of atomic orbitals and the
  properties of e? in orbitals
• 1st three quantum s indicate the main energy
  level, the shape and the orientation of an
  orbital
• 4th spin - describes a fundamental state of
  the e that occupies the orbital

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Principle Quantum -n

• Indicates the main energy level occupied by the
  e
• n-positive integers- 1,2,3
• As n increases, the es energy and its av.
  distance from the nucleus increases
• n1, occupies the 1st or lowest main energy level
  and is located closest to the nucleus

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n

• More than one e can have the same n value
• These es are sometimes said to be in the same
  e shell or main energy level
• When n1, 2 e can fit
• When n2, 8 e can fit
• How many e will fit when n3 and n4?
• Answers 18, 32

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On your own

• What is the value of n for electron in H?
• What is the value of n for the last e in Cl?
• What is the value of n for the last e in Cu?
• Answers n1, n3, n4

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Angular Momentum Quantum -l

• Indicates shape of orbital
• Sublevels orbitals of different shapes
• Sublevels exist for a given value of n except for
  the 1st main energy level
• The of orbital shapes possiblen
• l 0 and all possible integers less than or equal
  to n-1

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Examples

• When n2
• How many shapes are there?
• Answer 2
• What is l equal to?
• n-1 or (2-1)
• So l 1 and l 0

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Orbital Letter Designations for values of l

0 s
1 p
2 d
3 f
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Sublevels

• s-spherical
• p-have dumbbell shapes
• d-more complex
• f- too complex

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Try This

• When n1, how many orbitals does it have, what is
  the value for l and which sublevel is it in?
• When n2?
• When n3?
• When n4?

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Answers

• When n1, there is only 1 orbital, l0 and it is
  only in the s sublevel
• When n2, there are 2 possible orbitals, l0 and
  1, and it is in the s and p sublevels
• When n3, there are 3 possible orbitals, l0, 1
  and 2, and it is in s, p,and d sublevels
• When n4, there are 4 possible orbitals, l0,1,2
  and 3, s,p,d,f sublevels

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Magnetic Quantum -ml

• Indicates the of orbitals per
  sublevel(orientations)
• Atomic orbitals can have the same shape, but
  different orientations around the nucleus
• When l0, m0
• When l1, m-1,m0,m1(3 orientations)
• When l2, m-2,m-1,m0,m1,m2
• (5 orientations)

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Spin Quantum ms

• An e in an orbital can be thought of as spinning
  on an internal axis
• It spins in 1 of 2 possible directions or states
• As it spins, it creates a negative field
• 2 possible values 1/2 and 1/2
• A single orientation can hold a maximum of 2 e
  which must have opposite signs

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Electron Configuration

• The arrangement of e in an atom
• Each atom of each element has its own
• e arrange themselves so that they have the
  lowest possible energies
• The lowestenergy arrangement of the es is
  called the elements ground-state config.
• There are rules that allow us to determine these
  ground-state configurations

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Aufbau Principle-1st Rule

• Shows the order in which es occupy orbitals
• An e occupies the lowest-energy orbital that can
  receive it
• Figure 11.32 (atomic orbitals in order of
  increasing energy)
• Which orbital has the lowest energy? What about
  the next lowest energy?

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Aufbau cont

• What looks strange about the order as energy
  increases?
• Beginning with n3, the energies of the sublevels
  in different main energy levels begin to overlap
• The 4s sublevel is lower in energy than the 3d
  sublevel, so the 4s orbital is filled before any
  es enter the 3d orbitals

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Why?

• Less energy is required for 2 es to pair up in
  the 4s orbital than for a single e to occupy a 3d
  orbital
• What sublevel is filled next after 3d?
• Pauli Exclusion Principle-no two es in the same
  atom can have the same set of quantum s ( 3 are
  the same)

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Pauli Exclusion Principle

• 2 es can occupy the same orbital, but must have
  opposite spins
• Each arrow represents 1 of the atoms 2 es
• The direction of the arrow represents the es
  spin

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Hunds Rule

• Orbitals of equal energy are each occupied by 1 e
  before any orbital is occupied by a 2nd e
• All es in singly occupied orbitals must have the
  same spin
• e-e repulsion is minimized so e arrangements can
  have the lowest energy possible
• What is the max of unpaired es in a d sublevel?

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Representing e configurations

• 3 notations
• 1)orbital notation
• 2)e configuration notation
• 3)noble-gas notation
• Orbital Notation
• _____unoccupied orbital
• Orbitals name is written below the line nl