Chapter 7:

Atoms and Light

Low ν

High ν

Electromagnetic Radiation

WMHB broadcasts at 89.7 on the FM dial (89.7 MHz). What is the wavelength of the emitted radio waves?

The AM dial ranges from 500-1800 kHz. What wavelengths does this represent?

A microwave oven (2.4 GHz)?

Electromagnetic Spectrum

Constructive and Destructive Interference

Atomic Spectra

PotassiumHydrogen Helium Lithium Sodium

Atomic Spectra

The Hydrogen Atomic Spectrum

Quantum Theory (Blackbody Radiation)

Max Planck: E = hν

The energy required to break a carbon-carbon bond is approximately 360 KJ/mol. What wavelength of electro-magnetic radiation can supply this amount of energy?

The Photoelectric Effect

• Heinrich Hertz (1888) discovered that light striking the surface of certain metals causes ejection of electrons - the photoelectric effect.

• Electrons were only ejected if the frequency of the light () was above a certain threshold frequency (o)

• The number of electrons ejected were proportional to the intensity of the light

• The velocity (kinetic energy) of the electrons ejected was proportional to the frequency of the light

• Einstein used Planck’s ideas to explain the photoelectric effect:

ΔE = hν-hνo

Emission and Absorption Spectroscopy

The Bohr Atom

Hydrogen Energy Levels

A New Quantum Mechanics

The Heisenberg Uncertainty Principle

Δx Δp ≥ h

4π

Standing Waves

2Ln

= n = 1, 2, 3…

In a standing wave, the nodes remain at a constant position.

Standing Waves

Shrodinger suggested that electrons can be described as standing waves orbiting the nucleus, and used a mathematical equation to represent these waves.

The Schrodinger Equation: Wave Functions

Ψ (psi), the wave function.Corresponds to a standing wave within

the boundary of the system being described.

The energy of the standing wave increases as we add more nodes.

Probability of Finding an Electron

Quantum Numbers

By using three different quantum numbers, we can describe the wavefunction of any electron in an atom.

n : the principle quantum numberDesignates electronic shell (distance from nucleus), n = 1, 2, 3…

[It also corresponds to the number of radial nodes]

l : The angular momentum quantum numberDesignates the shape of the orbital, l = 0, 1, 2…(n-1)

ml : The magnetic quantum number

Describes the orientation of the orbital; ml = - l …-2, -1, 0, 1, 2…+l

l = 0, the “s” orbitals

l = 1, the “p” orbitals

ml for the “p” orbitals

l = 2, the “d” orbitals

Orbital Occupancy

Each orbital (described by 3 quantum numbers) can contain two electrons.

No two electrons can have the same set of quantum numbers.

Therefore…

The Fourth Quantum Number, s

Electrons have a spin of either +1/2 or –1/2. Electrons that occupy the same orbital must have opposite spins.