Quantum model of an Atom Chapter 17

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# Quantum model of an Atom Chapter 17 - PowerPoint PPT Presentation

Quantum model of an Atom Chapter 17. 0 of 250. 10. I read Chapter 15 before coming to class. Yes, the whole thing. Nope, essentially none. Well some, more than ½. A little only. 250. 0. The wave nature of moving particles is interpreted as being.

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0

of

250

10

I read Chapter 15 before coming to class
• Yes, the whole thing.
• Nope, essentially none.
• Well some, more than ½.
• A little only.

250

0

The wave nature of moving particles is interpreted as being
• An up and down path that the particle travels in as it moves.
• A back and forth path that the particle travels in as it moves.
• Not a traditional wave at all but instead is a function that tells us the probability of detecting the particle.

Newton’s Laws ok

Perspective

large small

fast

slow

Relativity

Wave-Particle Duality

250

0

10

Standing waves are created when
• Waves reflect and bounce back to where they started from.
• Waves wrap around and come back to where they started from.
• Both 1 and 2 are ways standing waves can be created.
2 Dimensions
• It is easy to create standing waves in 2 dimensions as well.

Two waves on a drum head

A single wave on a drum head

Three waves on a drum head

Wrap standing waves around a point
• These are patterns of vibration.
Bohr Model Explained!
• Take de Broglie’s waves and wrap them in a standing wave pattern around the nucleus.
• Put one wave , then two waves, then three waves, etc and you exactly predict the location of the Bohr radii!

A CRUDE representation!

The Quantum Model of the Atom
• Electrons are found in 3-D electron probability waves.
• They do not orbit. Instead they exist in the locations given by standing wave clouds.
• We call these wave clouds orbitals to reflect the fact that the electrons do not orbit like a planet.
The shape and energies of the actual orbitals depend on the number of standing waves in the pattern. They are found from solving the Shrödinger Wave equation:

h2 d2Y(x)

8 p2m dx2

+ V(x) Y(x) = EY(x)

Three Dimensional Atomic Orbitals

Kinetic Energy + Potential Energy = Total Energy

Orbital Patterns
• One wave:
• Electrons will resonate in one pattern, called an “s” orbital.
• Two waves:
• Electrons will resonate in two patterns, “s” and “p” orbitals

s

s

p

Orbital Patterns
• Three waves: Electrons will resonate in “s”, “p” and “d” orbitals.

One orbital

s

p

d

S Orbitals
• All numbers of standing waves have “s” orbitals.
• They are all round but their interiors are different.
• Still, in each case there is just one orbital.
P Orbital
• P orbitals come in sets of 3, whether there are 2 waves or 3 waves or more.
D Orbitals
• D orbitals come in sets of 5, whether there are 3 waves or 4 waves or more.
Orbital Patterns
• The pattern continues on as s, p, d, f, g, h, i, j, etc. Each new orbital set has two more orbitals than the previous one.

e

-

e

-

The Pauli Exclusion Principle
• At most two electrons can occupy the same orbital. If two electrons are in the same orbital, they must have different spins.

Spin Down Spin Up

High energy

Low energy

1

2

3

Understanding Atoms
• How do electrons fill the orbitals as we move along the periodic table?
• Electrons fill the lowest energy levels first. For the lighter atoms, fewer standing waves and simpler orbitals usually means lower energies.
• From here on I’ll refer to number of standing waves (physics lingo) as energy levels or shells (chemistry lingo).
Electrons in an Atom: Energy WellsFill the lowest energy orbitals first

free electron

Zero Energy

3d

3p

3s

Level 3

2p

Level 2

2s

Energy

It is negative for a bound electron

Level 1

1s

Hydrogen

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Helium

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Lithium

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Beryllium

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Boron

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Carbon

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Nitrogen

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Oxygen

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

250

0

10

• 3
• 5
• 9
• 16

250

0

10

How many electrons total are in an atom that has the first and second shells completely filled?
• 4
• 6
• 10
• 12
Absorption line spectra revisited
• The outer electron of any atom can jump up to higher orbitals creating a unique absorption spectrum for that element

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s

Emission line spectra revisited
• It can then fall down creating the emission spectrum for that element.

free electron

3d

3p

3s

Level 3

2p

Level 2

2s

Level 1

1s