11/10/16 Today I will define the characteristics of a wave and compare the major regions of the electromagnetic spectrum. Warm Up – What are the three types of energy we discussed in a previous chapter?

Chapter 4 – Electron Configuration Part 1 - Waves

Radiant Energy Light Properties of both a particle and a wave! We call this the dual nature of light

Nature of Light Einstein proposed that: The particles or “packets” of light are called “PHOTONS” Light travels in waves We use four main terms to define the characteristics of these waves

Waves Wavelength (λ) units in meters (often nm) distance between successive crests (high points) or troughs (low points) units in meters (often nm)

Waves Amplitude (A) height of the wave (from origin to crest) units in meters Brightness of light

Waves Frequency () – how fast the wave is moving up and down how many waves pass a fixed point in a given time units in per seconds or Hertz (Hz) Notice that the higher the frequency, the shorter the wavelength.

Wave Speed (c) – how fast light moves through space All light (regardless of wavelength) moves through space at the speed of light! c = 3.00 x 108 m/s

Electromagnetic Spectrum Visible light is only one form of radiant energy. 7 Parts of the Electromagnetic Spectrum Longest wavelength to Shortest: Radio Microwaves Infrared Visible Light U.V. Light X-Rays Gamma-Rays

Homework 4-1 Review & Reinforcement (except #3)

11/11/16 Today I will determine the mathematical relationships in the electromagnetic spectrum Warm up – Draw a wave and label the origin, amplitude, wavelength, crest, and trough. Now draw a wave with a larger frequency. Does it have a longer or shorter wavelength?

Wave Relationships We said that wavelength and frequency are inversely related When one goes up, the other goes down.

Wave Relationships Mathematical Relationship Notice that speed of light is in m/s so… FIRST! Wavelength must be in meters and frequency must be hertz (/s)!

Wave Relationships For example: Wavelength is often given in nm. You must convert first! So 415 nm = ? m 1 m = 1x109nm

Wave Relationships A helium-neon laser produces a red light whose wavelength is 633 nm. Calculate the frequency of the radiation.  = 4.74 x 1014 Hz Do you remember what to do when the variable is on the bottom???

Wave Relationships What is the wavelength of U.V light that has a frequency of 4.50 x 1016 Hz? Answer: 6.67 x 10 -9 m

Wave Relationships An interesting note: Radios broadcast using waves. FM radio uses waves in the MHz range. AM radio uses waves in the kHz range.

Wave Relationships What is the wavelength of a radio wave that broadcasts at 600 AM? 600 AM = 600 kHz Convert from kHz to Hz Answer: 500 m 1 Hz = 0.001 kHz

Homework Wavelength & Frequency Calc

11/14/16 Today I will Determine relationships between energy and waves Solve for energy Warm Up – What is the frequency of light that has a wavelength of 245 nm?

Wave Relationships - energy The higher the frequency, the more energy.

Wave Relationships - energy Maxwell Plank E=h Where E is energy h is plank’s constant  is frequency Plank’s constant = 6.626 x 10-34 J·s Energy and frequency are directly proportional When one goes up, the other goes up!

Wave Relationships - energy What is the energy of U.V. light with a frequency of 4.50 x 10 16 Hz? E = h  E = (6.626 x 10 –34 Js)(4.50 x 10 16 Hz) E = 2.98 x 10 –17 J

Wave Relationships - energy Determine the energy of light that has a wavelength of 450nm. Do we know anything about wavelength and energy? E=h

Wave Relationships - energy Determine the energy of light that has a wavelength of 450nm.

Homework Electromagnetic Radiation - Energy Calculations

11/15/16 Today I will review the electromagnetic spectrum & calculations Warm Up – How much energy is in a wave whose wavelength is 432 nm?

11/16/16 Today I will explain the quantization of light Warm Up – What is the relationship (in words) between: Wavelength and frequency Frequency and energy Wavelength and energy

Quantization of Energy Scientists were confused by the observation that the wavelength of the radiation changed with temperature

Quantization of Energy Maxwell Planck – proposed that there are fixed amounts of energy that an object emits. He called each of these pieces of energy a quantum. Quantum means a fixed amount

Quantization of Energy What is the difference between quantized and continuous? Going up a ramp going up steps If energy is in quanta, why aren’t we aware of it? Quanta of energy are very, very small. Too small to notice.

Quantization of Energy We have seen that not all light is the same. We are surrounded by radio waves every day and they do not harm us, but gamma rays are very dangerous. Very energetic light is dangerous (UV, X-rays, gamma) Low frequency light does not have enough energy to be dangerous.

Photoelectric Effect Electrons can be ejected from the surface of a metal when light shines on it. Not all lights will cause this to happen on all metals. For example. Red light is not able to release electrons from sodium, but violet light is.

Photoelectric Effect Einstein proposed the idea of photons of light. Some photons have enough energy to release the electrons of a given metal and some do not. One Quantum = One PHOTON Compton said that Light packets collide with the electrons to release them. You can’t add the energy up as more light hits, so either a photon will release the electron or not.

Photoelectric cells One everyday use of the photoelectric effect is photoelectric cells. Automatic lights Automatic doors When the light shines, electrons are emitted and a current is produced. When that light is broken (by darkness or a body crossing it), the current is shut off and the desired effect is triggered.

Homework 4-2 Review & Reinforcement

11/17/16 Objective – to describe the Bohr model of the atom Warm Up – Which light will have a greater chance of producing the photoelectric effect: radio waves or ultraviolet waves? Why?

Bright Line spectra Remember the idea that things changed colors when heated.... When certain salts are heated, they produce colorful light!

Bright Line spectra These distinct colors are known as that element’s continuous spectrum Lithium – red Potassium – purplish pink Sodium - yellow

Bright Line spectra Sometimes difficult to differentiate colors When these lights are passed through a prism, they separate into distinct lines. These combinations of lines are called line spectra Bright Line spectra are unique to certain elements

Bohr Model Neils Bohr – 1911 Wanted to explain line spectra Electrons orbit the nucleus in defined energy levels Gave each level a quantum number (n)

Bohr Model When energy is absorbed, an electron can “jump” to a higher energy level Energy absorbed

Bohr Model These electrons then “fall” back down and release energy. This energy is released as light.

Bohr Model Ground State- when an electron is on the energy level at which it normally resides Excited State – when an electron is on a higher energy level than usual

Bohr Model Excited state Ground state Energy absorbed Ground state Energy released as light In this example, n=1 is the ground state and n=2 is the excited state

Bohr Model

Bohr Model The amount of energy released is determined by how that atom’s electrons jump and fall. The wavelengths (or colors) of light are determined by those energies!

Bohr Model Bohr’s model and the calculations of energy and wavelength work very well for Hydrogen. However, with larger atoms, the model works only approximately. Ultimately, this model does not work, but it was a good starting point for scientists, especially in thinking of distinct energy levels!

Today I will review chapter 4 (part 1) 11/18/16 Today I will review chapter 4 (part 1) Warm Up If light has an energy of 1.2 x 10-20 J, what is its wavelength? c = 3.00 x 108 m/s h=6.626 x 10-34 J·s

Homework Chapter 4 Review

11/21/16 Today I will prepare for the chapter 4 (part 1) test Warm Up – Explain the dual nature of light.