Homework

• 6.3 and 6.4 Notes and Vocab

• Give it some thought page 226 and 231

• Quiz Thursday (can use homework and notes)

Homework Quiz

• Define quantum

• Give it some thought question page 218 (6.1)

Einstein used quantum theory to explain photoelectric effect.

When photons of significant high energy strike a metal surface – electrons are emitted from the metal

Photocell - emitted electrons are drawn toward positive terminal creating an electrical circuit

Emission Line Spectra

Emission Line Spectrum of H

H gas is excited by electrical voltage and emits light of only certain energies - givings a specific emission line spectrum

Niels Bohr

Physicist

1885 – 1962

Bohr used Plank’s quanta concept and applied it to matter. He said that e- are organized in quantized energy levels around the nucleus.

Bright Line Spectrum

• Bohr proposed that the energy possessed by an e- in a H- atom and the radius of the orbit are quantized (bls)– Quantized (definition): a specific value (of energy)

The ramp is an example of a continuous situation in which any energy state is possible up the ramp

Like a set of stairs, the energy states of an electron is quantized – i.e. electrons are only found on a specific step

Bohr’s postulates• Electrons are permitted ONLY in orbits of certain radii, that

correspond to specific energies• An e- in a permitted orbit has a specific energy and is in an

“allowed” energy state. An e- in an allowed energy state “is happy” and will not radiate energy(stays in that orbit)

• Energy is emitted or absorbed by e- ONLY as it changes from one allowed energy state to another

Bohr’s Energy Absorption Process

• Light or energy excites an e- from a lower energy level (e- shell) to a higher energy level

• These energy levels are “ quantized “ (the e- cannot be in between levels), the e- disappears from one shell and reappears in another

• This absorption or excitation process is called a quantum leap or quantum jump

Bohr’s Energy Absorption Process

• Ground State Analogy = a spring and two balls

This is an energy emission process and

what we observe in the hydrogen line spectrum

Both the atom and e- now have higher

energyThe e- absorbs energy in the ground state and is

excited to a higher level

Evidence for Energy Levels• When electrons are excited (absorb energy) they can no

longer be that same “allowed” energy level• So the electron must “jump” up to a higher “allowed”

energy level• The electron(s) are NOT “stable” (“happy”) in the excited

state (higher energy level…SO, in order to get back down they emit energy as photons of light

• SINCE we see different colors of light in the line spectra, this means electrons are moving down from different energy levels

H Line Spectra

Evidence for Energy Levels• The red line corresponds to excited e dropping from energy level 3

to 2• The blue-green line corresponds to an excited e dropping from

energy level 4 to 2• The violet line corresponds to an excited e dropping from energy

level 5 to 2

Bohr’s Energy Absorption Process

• The atomic line spectral lines - when an e- in an excited state decays back to the ground state

The electron loses energy, light (colors) is emitted and the e- returns to the ground state

This is another illustration of bls.

The Electromagnetic Spectrum

• ROYGBIV - colors of the visible spectrum • Bright Line Spectrum (BLS) – caused by e- emitting

energy as they return to lower energy levels energy level.

• heat sodium - yellow light• heat lithium - red light• elements can appear to give off the same color light, but

each will have its own BLS• BLS - used to determine identity of an element• BLS - validates Bohr’s idea that electrons jump to different

energy levels and give off different wavelengths of light

Problem with Bohr’s model

• Bohr’s model gave explanation of emission line spectra of H, HOWEVER, it cannot explain the spectra of other atoms

• Emission spectra of atoms other than H, had more spectral lines than could simply be explained by Bohr’s model ((electrons act as particles and move from energy level to energy))

Wave-particle duality of matter• After Bohr, depending on experimental

conditions, radiation appeared to have either wave or particle-like character; so if radiation could act like a particle WHY couldn’t matter(particles) act like a wave???

Heisenberg Uncertainty Principle

• there are limits to our ability to measure both a particle’s velocity and its position at the same instant

Heisenberg Uncertainty Principle• limitations on measuring speed and position are not

significant for large objects BUT for small particles (e-) these limitations prevent us from knowing or being able to predict where an e- is at a given instant

• states that one cannot assign with full precision values for certain pairs of observable variables, including the position and momentum, of a single particle at the same time

• therefore, we cannot accurately predict where a particle will be with 100 % certainty, we can only speak in terms of probabilities

Heisenberg Uncertainty Principle

• Office calls looking for a student

• Knows what classroom

• Uncertain where in the student sits.

Schrödinger Equation

• uses a wave function to predict where an electron might be at any given time

• Gives the probability of finding electron at a specific position

Intro to Quantum Leap Lab

• Background: – Read and underline– Be prepared to discuss

• Read Procedure– Be prepared to discuss