Physics and the Quantum Mechanical Model l OBJECTIVES: - Calculate the wavelength, frequency, or energy of light, given two of these values.

Section 13.3 Physics and the Quantum Mechanical Model l OBJECTIVES: - Explain the origin of the atomic emission spectrum of an element.

Light l The study of light led to the development of the quantum mechanical model. l Light is a kind of electromagnetic radiation. l Electromagnetic radiation includes many kinds of waves l All move at 3.00 x 10 8 m/s = c

Parts of a wave Wavelength Amplitude Origin Crest Trough

Parts of Wave - p.372 l Origin - the base line of the energy. l Crest - high point on a wave l Trough - Low point on a wave l Amplitude - distance from origin to crest l Wavelength - distance from crest to crest Wavelength is abbreviated by the Greek letter lambda =

Frequency l The number of waves that pass a given point per second. l Units: cycles/sec or hertz (hz or sec -1 ) Abbreviated by Greek letter nu = c =

Frequency and wavelength l Are inversely related l As one goes up the other goes down. l Different frequencies of light are different colors of light. l There is a wide variety of frequencies l The whole range is called a spectrum, Fig , page 373

Radio waves Micro waves Infrared. Ultra- violet X- Rays Gamma Rays Low energy High energy Low Frequency High Frequency Long Wavelength Short Wavelength Visible Light

Prism l White light is made up of all the colors of the visible spectrum. l Passing it through a prism separates it.

If the light is not white l By heating a gas with electricity we can get it to give off colors. l Passing this light through a prism does something different.

Atomic Spectrum l Each element gives off its own characteristic colors. l Can be used to identify the atom. l How we know what stars are made of.

These are called discontinuous spectra, or line spectra unique to each element. These are emission spectra The light is emitted given off Sample 13-2 p.375

Light is a Particle l Energy is quantized. l Light is energy l Light must be quantized l These smallest pieces of light are called photons. l Photoelectric effect? l Energy & frequency: directly related.

Energy and frequency E = h x l E is the energy of the photon is the frequency l h is Planck’s constant l h = x Joules x sec. l joule is the metric unit of Energy

The Math in Chapter 11 l 2 equations so far: c = E = h l Know these!

Examples l What is the wavelength of blue light with a frequency of 8.3 x hz? l What is the frequency of red light with a wavelength of 4.2 x m? l What is the energy of a photon of each of the above?

Explanation of atomic spectra l When we write electron configurations, we are writing the lowest energy. l The energy level, and where the electron starts from, is called it’s ground state- the lowest energy level.

Changing the energy l Let’s look at a hydrogen atom

Changing the energy l Heat or electricity or light can move the electron up energy levels (“excited”)

Changing the energy l As the electron falls back to ground state, it gives the energy back as light

l May fall down in steps l Each with a different energy Changing the energy

{ { {

l Further they fall, more energy, higher frequency. l This is simplified l the orbitals also have different energies inside energy levels l All the electrons can move around. Ultraviolet Visible Infrared

What is light? l Light is a particle - it comes in chunks. l Light is a wave- we can measure its wavelength and it behaves as a wave If we combine E=mc 2, c=, E = 1/2 mv 2 and E = h We can get: = h/mv l called de Broglie’s equation l Calculates the wavelength of a particle.

Sample problem l What is the approximate mass of a particle having a wavelength of meters, and a speed of 1 m/s?  Use = h/mv = 6.6 x (Note: 1 J = N x m; 1 N = 1 kg x m/s 2

Matter is a Wave l Does not apply to large objects l Things bigger than an atom l A baseball has a wavelength of about m when moving 30 m/s l An electron at the same speed has a wavelength of cm l Big enough to measure.

The physics of the very small l Quantum mechanics explains how the very small behaves. l Classic physics is what you get when you add up the effects of millions of packages. l Quantum mechanics is based on probability

Heisenberg Uncertainty Principle l -It is impossible to know exactly the location and velocity of a particle. l The better we know one, the less we know the other. l Measuring changes the properties. l Instead, analyze interactions with other particles

More obvious with the very small l To measure where a electron is, we use light. l But the light moves the electron l And hitting the electron changes the frequency of the light.

Moving Electron Photon Before Electron Changes velocity Photon changes wavelength After Fig , p. 382