Chem Honors: Quantum Mechanics & Quantum Model

What were the problems with the Bohr model?

1) Multielectron atoms didn’t have the energy levels predicted by Bohr models.

2) Double and triple bands appear in emission spectra, model does not have explanation for why some energy levels are very close together.

What are quantum mechanics?

Revolutionary atomic theory that explains behavior of exceedingly small particles, like atoms and subatomic particles. Based on very strong evidence that very small particles, like electrons, do not behave lie anything we have experienced.

What is the most accurate tested physics theory?

Quantum mechanics

What things do quantum mechanics explain?

1) The energy state in complex atoms/molecules.

2) Relative brightness of spectral line.

What are the two ways electrons behave like? What is this called?

Particles of matter and waves of light and sound. Wave-particle duality.

Who conducted the Nobel Prize winning “Double-Split” experiment?

Davisson and Germer of Bell Labs

What did the “Double-Split” experiment show?

An electron transitioning from acting like a particle, to acting like a wave, back to acting like a particle.

Explain the “Double-Split” experiment.

Electrons are shot one at a time towards a barrier with two slits. As particles, each electron should go through one slit of the other, creating two bands where they strike the observing screen. Actually a pattern emerges, which shows that each electrons acts like a wave and passes through both slits. Then it acts like a particle again when striking the observing screen.

What does the “Double-Split” experiment show?

Wave-particle duality.

Which two people made major contributions to physics during the early 20th century?

Heisenberg with his Uncertainty Principle and by Schroedinger with his wave equation.

What was Schröedinger’s experiment?

Treating electron as a wave, Schröedinger’s wave equation described the probability of finding an electron at each location within atoms or molecules.

Why is the Bohr picture of an atom with its electrons in neat orbits wrong?

We can’t say exactly where an electron is.

What is the quantum theory?

Electron probability distribution; this figure shows probability distribution for ground state of hydrogen.

What is the probability of finding an electron at a location represented by?

Density of dots at a location.

What are the 4 different quantum numbers.

N, l, m<l, m<s

What are quantum numbers used for?

To specify state of probable location of an electron in an atom.

What is the n?

Principal; energy level/distance from nucleus.

What is the l?

Angular; the shape of the orbital.

What is the m<l?

Magnetic; orientation of orbital in space.

What is the m<s?

Spin; the direction of electron spin.

What is an orbital?

A regional of space where electron is most likely to be found.

What _____ the value of n, the ______ from the nucleus the electron will likely be found.

Larger, farther.

What is a subshell?

An orbital region.

What are the 4 shapes of orbitals?

S, p, d, f

What is the S subshell?

Spherical in shape.

The radius of the sphere _______ with the value of __.

Increases, n.

Fill this out:

If I = S shape

M<l = ______

__ orbital per energy level.

M<l = 1

1 orbital per energy level

What are P orbitals?

Orbitals with 2 lobes with a node between them.

For P orbitals, what does the electron density and probability of finding an electron depend on?

Both the distance and direction from center of atom.

Since the P subshell has 3 possible arrangements in space, how many orbitals can it have?

3

Fill out:

I = P shape

M<l= ___ orientations

__ orbitals per energy level

M<l= 3 orientations

3 orbitals per energy levels

What do d orbitals have that the others don’t?

A more complex shape.

If the d subshell has 5 possible orientations in space, how many possible d orbitals is there?

5

How many possible orbitals in the f sub shell?

7

What was discovered in the 1920s that led to a fourth quantum #?

That two electrons in the same orbitals do not have exactly same energy.

What is the fourth quantum?

The spin quantum #, m>s

What does the spin of an electron describe? What does it affect?

It’s a magnetic field. It’s energy.

What can the spin quantum # be?

(+) or (-)

What does the fact that the spin quantum can be + or - imply?

That electrons are in some way able to pair up, even though they repel each other due to the electromagnetic force.

How many electrons can each orbital hold then, taking into consideration that electrons are in some way able to pair up?

A max of 2 electrons.

What is specified by the quantum state of an electron?

The 4 quantum #s.