Quantum Mechanics Overview

1. Quantum Mechanics Overview Quantum: (Latin, "how much") refers to discrete units (packets/bundles/particles/chunks) that this theory assigns to certain physical quantities (for example energy)Mechanics: branch of physics that deals with atomic and subatomic systems based upon the discovery that waves could be measured in particle-like small packets of energy called quanta

2. Current Atomic Model: Early 1900’s Rutherford Model of the atom: concluded through their experimentation that the atom had a nucleus with an overall positive charge and negative electrons orbiting the center this model did a poor job explaining why negative electrons didn’t attract to the positive nucleus this model did a poor job how the electrons were arranged at all this model didn’t account for the different behavior of apparently similar chemicals

3. Light: Behave like a Wave What is a wave? a disturbance that propagates through space, often transferring energy.

4. Light: Behave like a Wave Classes of waves: mechanical waves: exist in a medium (travel through stuff) electromagnetic radiation waves: can travel through vacuum (without a medium)

5. Light: Wave Properties Describing Waves frequency (ν): number of waves that pass through a point per second (unit: 1/s or Hertz (Hz)) wavelength(λ): distance between peaks or troughs (unit meter with appropriate prefix) amplitude (A): height of the wave (unit meter with appropriate prefix)

6. Light: Wave Properties Electromagnetic Radiation: energy that can travel through empty space in a wavelike fashion at the same speed (c =3.00 x 108 m/s)

7. Light: Wave Properties c= λ ν Electromagnetic Radiation: the relationship between frequency (ν) and wavelength(λ) is inverse and the multiplication equals c (3.00 x 108 m/s). With higher frequency comes shorter wavelength and vice versa.

8. Light: Wave Properties Interference Pattern:look that the following experiment and predict what will happen Light behaves as a wave with a characteristic frequency (ν), wavelength(λ), and amplitude (A).

9. Light: Wave Properties Interference Pattern: Constructive Destructive the waves addthe waves cancel

10. Light: Behave like a Particle? Max Planck: wanted to see why light of only certain colors was emitted from excited gases or heated metals He looked at emission spectraexamples

11. Light: Behave like a Particle? Particles of light are called photons. Effect of photons on electrons. Planck found Equantum=hν where E is energy, h is Planck’s Constant (6.626 x 10-34 J.s and J is Joule the SI unit of energy) and ν is frequency

12. Light: Behave like a Particle? Photoelectric Effect: electrons are emitted from the surface of a metal only when light of a specific frequency is shone Wave model of light predicts that with enough low frequency light energy could build up and emit electrons from the surface of a metal

13. Light: Behave like a Particle? Photoelectric Effect: electrons are emitted from the surface of a metal only when light of a specific frequency is shone However, this was not the case because all metals seemed to have a threshold frequency below which photoelectric electron ejection did not occur This led Einstein to expand on Planck’s ideas and state Ephoton=hν where E is energy, h is Planck’s Constant (6.626 x 10-34 J.s and J is Joule the SI unit of energy) and ν is frequency.

14. Current Atomic Model: Early 1900’s Bohr Model of the atom: agreed that the atom had a positive nucleus but using the recently discovered ideas of Planck & Einstein, stated that electrons orbited the nucleus at certain specific distances and subsequently energy levels (n) this model did a good explaining why negative electrons didn’t collapse into the positive nucleus this model only predicted correct results for hydrogen’s atomic spectra this model did make the false assumption that electrons orbit the nucleus like planets around the sun

15. Electrons: Wave Properties? Interference Pattern: look that the following experiment and predict what will happen much to the surprise of experimenters electrons exhibited the same interference patterns in a two slit experiment similar to that with light reinforced the idea that light had particle like properties (the quantum) this led to the conclusion that electrons had wave like properties

16. Quantum Concept De Broglie Model of the atom: agreed with Bohr but stated electrons behave as waves as described by the De Broglie Equation λ =h/mv where λ is wavelength, h is Plank’s Constant, m is mass, and v is velocity. this early quantum mechanical model did a good explaining why negative electrons didn’t collapse into the positive nucleus it also explained why different elements only emitted specific colors of light when excited

17. Quantum Concept Consequence of the Quantum Concept: Heisenberg Uncertainty Principle: it is not possible to know both the position and velocity of electrons because light must be shone on electrons to determine their position which will then change their velocity

18. Quantum Concept Schrodinger: agreed with Bohr but considering the Heisenberg Uncertainty Principle calculated the probability of finding an electron (as a wave/ particle) in a given 3D space the 3D space is called an atomic orbital and represents a 90% probability of finding an electron at a given energy level worked for all elements

19. Quantum Concept Schrodinger’s Atomic Orbitals: calculated that different energy levels (n) had different shapes and sizes n (the principal quantum number) can range 1-7 as n increases the number of possible different shapes (which are called sublevels) increases each sublevel (s, p, d or f) has a certain number of atomic orbitals (s=1, p=3,d=5,f=7) each atomic orbital has a capacity of two electrons