1. Electromagnetic Radiation
Ms. Marshall
Chemistry
WW-P

2. Properties of Radiation
How does electromagnetic energy present itself?
What parameters can be measured?
How was quantum theory developed?

3. Einstein’s Photoelectric Effect
Quantum Theory
Einstein’s Photoelectric Effect
What is the photoelectric effect?
The frequency of radiation is
what matters – not the intensity
Nobel prize in 1919
Experimental support Planck’s quantum theory.
Quantum is a “packet” or “bundle” of energy
Wave-particle duality – radiation has properties of both particles and waves

4. Radiation Properties Radiation is classified as electromagnetic energy
Electromagnetic radiation is energy traveling through space that has wave-like properties.
Parameters: frequency (ν), wavelength (λ), amplitude, energy (E)
What is the relationship between λ and ν?
How are both variables related to E?
All ER waves travel at the speed of light!!
2.998 x 108 m/s.

5. Why does this matter?
Atomic structure was identified by looking at spectra
because they are unique we can identify elements based on their spectra
We use what we have learned about the atoms using their spectra to classify them in the Periodic Table

6. Electromagnetic Spectrum
Source: Wilbraham, A.C., et. Al. Chemistry, 2005

7. Essential Question
Why don’t atoms give off a continuous spectra?

8. Bohr’s Model of the Atom
1913 – Rutherford’s Nuclear Model of the atom was changed.
New discoveries about how the energy of an atom changes when it absorbs or emits light were included
Bohr’s model is based on Hydrogen atoms only
Proposed that electrons travel only in specific circular paths, or orbits, around the nucleus.
Worked well for Hydrogen, not for other atoms.

9. Bohr’s Model of the Atom
Each possible e- orbit has a fixed energy called energy levels

10. Check for Understanding
If an electron absorbs energy to change energy levels, how much energy will it absorb.
Less than the amount of energy of the “new” energy level
More energy than the amount of energy required for the “new” energy level
Just enough energy to have the same energy as the “new” energy level
An amount of energy equal to the energy of the new energy level

11. Bohr’s Model of the Atom
The amount of energy an e- gains or loses will not always be the same.
Energy levels are not equally spaced
This model failed to explain the energies absorbed and emitted for atoms other than hydrogen.

12. The Quantum Mechanical Model
Erwin Schrodinger
Based on new theoretical calculations and experimental results
Created and solved a mathematical equation describing the behavior of the e- in an H atom
Quantum mechanical model
The modern description, primarily mathematical, of the behavior of electrons in atoms
comes from solutions to Schrodinger’s equation

13. Quantum Mechanical Model
Differences from Bohr’s Model
Not an exact path for the e- to travel around the nucleus
Determines the allowed energies an e- can have and the probability of finding the e- in a location
Described by probability (4 marble examples)

14. How do these pictures relate to the probability of an e- being in certain place? Think-Pair-Share (1.5 minutes)

15. What is Quantum Mechanics
1905 – Albert Einstein
Explained experimental data that proposed that light could be described as quanta of energy.
Photons – a quantum of light;
1924 – Louis de Broglie
Light behaves as waves and particles, so can particles of matter behave as waves?
1927 – Clinton Davisson & Lester Bell Labs in NJ (confirmed de Broglie’s hypothesis)
Noticed that e- reflected from metal surfaces when bombarded with beams of e-.
Odd patterns – like x-rays reflecting from metal surfaces.

16. What is quantum mechanics?
Reflected as if they were waves.
This property of particles is used to create clear, enlarged images of very small objects.
Size of object needs to be very small to observe the wavelength.

17. What is quantum mechanics?
Classical mechanics
Describes the motions of objects much larger than atoms adequately
Quantum mechanics
Describes the motion of subatomic particles and atoms as waves

18. Heisenberg Uncertainty Principle
Werner Heisenberg (German physicist)
It is impossible to know exactly both the velocity and position of a particle at the same time.
Does not apply to large objects
Cars, airplanes

19. Atomic Orbitals
Solving Schrodinger’s equation tells you the energies an e- can have.
Also leads to a mathematical expression
atomic orbital
A region of space in which there is a high probability of finding an electron
Determined by the solutions to Schrodinger’s equation.

20. Where are the electrons ?
Ground state – most stable region closest to nucleus
Excited state – when energy is applied, electron absorbs energy and jumps to a region farther away from the nucleus; the electron immediately returns to stable ground state and emits energy (in the form of light)

21. Atomic Orbitals Principal quantum numbers (n)
Labels for energy levels
n = 1, 2, 3, 4, …
Each principal energy level can have a number of orbitals with different shapes at different energy levels. (sublevels)
Key Point
Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron will most likely be found.

22. Sublevels
Due to the spherical shape of the s orbital, the probability of finding an e- at a given distance does not depend on direction.

23. Sublevels

24. Sublevels

27. Electrons!!!
If all atoms are composed of the same fundamental building blocks, how is it that different atoms have vastly different chemically behaviors?