Electromagnetic Radiation and the Bohr Model of the Atom Objective: Students will understand the Bohr model of the atom by understanding light.

Review: Rutherford’s Model

Rutherford’s Contributions the nucleus of the atom is composed of protons and neutrons. That the nucleus is small The electrons are circling the nucleus.

Rutherford’s Failure He couldn’t explain why the negative electrons aren’t attracted into the positive nucleus, causing the atom to collapse. Video 15:15Video

A Strange Answer to a Strange Question Why doesn’t the electron fall into the nucleus? Because it isn’t allowed! To understand this unbelievable phenomenon, we must understand the nature of light

Neils Bohr We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. My own feeling is that it is not crazy enough.

What are the components of a wave? A wave has frequency, amplitude and wavelength

Frequency The # of peaks that pass by in a given amount of time Hz = 1/sec MHz = 1,000,000/sec KHz = 1,000/sec

Electromagnetic Radiation Name Several Types of electromagnetic Radiation(325)

How do waves differ? They have different wavelengths They have different frequencies They have different amplitudes

How are they different? They have different frequencies They also have different energies Click hereClick here to see how they differ Then hereThen here to see how they are the same!

What do they all have in common? They all travel at the speed of light 3.00 x 10 8 meter/sec

Wavelength and Frequency If the λ = 2 meters and υ = 10/sec, find the speed λ x υ = speed 2 meters x 10/sec = 20.0 meters/sec 5 meters x ______ = 20.0 meters/sec So frequency and wavelength are inversely proportional

KSL Radio’s Wavelength KSL broadcasts at 1160 KHz. Find the λ of KSL’s signal. 1160KHz = /sec Wavelength x frequency = speed λ x = 3.0 x10 8 m/sec (3.0 x10 8 m/sec)/( /sec) = 258 meters

FM or AM

What is a Photon Photons are light particles. A bundle of energy

Energy of Photons The energy of a photon is given by this equation E = υ h. The symbol “h” represents Planck’s constant. It has a value of

KSL 1160 Find the Energy of a photon of light produced by KSL (1160 KHz) E = υ h E = s -1 x x Js E = 7.69 x J

Energy and Frequency How are Energy and υ related? The higher the frequency the greater the energy. How are Energy and λ related? The lower the energy the longer the λ

Radio Waves Turn your book to page 325. What is the electromagnetic with the lowest energy?

Who or what is Roy G Biv? An acronym for the colors of the rainbow. It is not a person.

Hydrogen and Roy G Biv The colors emitted when energy is passed through hydrogen is

The Quantum Atom Atoms are quantized because they only emit light at certain frequencies and energies. A Quantum is the smallest quantity of radiant energy, equal to Planck's constant times the frequency of the associated radiation. E = h x frequency

A Staircase Not a Ramp Look at pg 330 Figure Like a staircase, the atom has specific energies. A ramp has infinitely small divisions.

What Does “N” represent? The Energy Levels inside the atom

What values can N have 1, 2, 3, …. In the hydrogen atom, where does the electron reside? In the lowest energy level or n=1 The electron can move up to higher energy levels by absorbing photons. We then say the electron is excited

A relaxing electron What happens when an electron relaxes? It falls from a high energy level to a lower one. What happens to the extra energy? It is emitted in the form of light. The further an electron falls the more energy it gives off

What Gives off the Most Energy? Higher Energy Lower Energy

Finding the energy of n=3 The equation to find the energy of the hydrogen energy levels is E = x J (1/N 2 ) E = x J (1/3 2 ) E = x J

Finding the difference between n=2 and n=3 For N=2, E = x J For N=3, E = x J What happens if an electron falls from N=3 to N=2? Just take n=2 and subtract n=3, that gives you ΔE ΔE = 3.0 x J

Calculate the υ E = υ h 3.03 x J = υ h 3.03 x J = υ x x Js υ = 4.57x Hz λ x υ = 3.03 x 10 8 meters/sec λ x 4.57x = 3.0 x 10 8 meters/sec λ = 6.56 x meters

The Lyman and Balmer series If an electron falls to n=1, the energy is to high for us to see. It can be detected but it falls into the UV spectrum

Ultra Violet, Infra Red, Visible Where the electron falls to determines the type of light it produces. If it falls to the n=3, it produces IR. We can only se it if it falls to the n=2

The absorption Spectrum

Quiz #1 1. What was the shortcoming of the Rutherford model of the atom? a. It couldn’t explain how the electron stayed in orbit. b. It couldn’t explain the existence of electrons. c. It couldn’t explain the existence of protons.

2. Who improved the Rutherford model? a. Dalton b. JJ Thompson c. Neils Bohr d. Max Plank

3. Who is the constant “h” named after? a. Dalton b. JJ Thompson c. Neils Bohr d. Max Plank

4. Which has the longest wavelength? a. Red Light b. UV Light c. IR Light d. Violet Light

5. Which form of electromagnetic energy has the most energy? a. Red Light b. UV Light c. IR Light d. Violet Light

6. Which element’s spectrum did Bohr explain? a. Helium b. Hydrogen c. Carbon d. Oxygen

7. Which has the lowest energy in the visible spectrum? a. Red Light b. UV Light c. IR Light d. Violet Light

8. Who found energy levels in the atom? a. Dalton b. JJ Thompson c. Neils Bohr d. Max Plank

9. W? a. b. c. d.

10. Which electronic transition gives off the most energy in the hydrogen atom? a. N2 to N1 b. N3 to N2 c. N4 to N3 d. N4 to N2