Outline Chapter 9 The Atom 9-1. Photoelectric Effect 9-2. Photons 9-3. What Is Light? 9-4. X-rays 9-5. De Broglie Waves 9-6. Waves of What? 9-7. Uncertainty Principle 9-8. Atomic Spectra 9-9. The Bohr Model Electron Waves/Orbits The Laser Quantum Mechanics Quantum Numbers Exclusion Principle

9-2. Photons Max Planck ( ) Max Planck in 1900 stated that the light emitted by a hot object (black body radiation) is given off. in discrete units or quanta. The higher the frequency of the light the greater the energy per quantum.

9-2. Photons The system shown here detects people with fevers on the basis of their infrared emissions, with red indicating skin temperatures above normal. In this way people with illnesses that may be infectious can be easily identified in public places.

9-2. Photons All the quanta associated with a particular frequency of light have the same energy. The equation is E = hf where E = energy, h = Planck's constant (6.63 x J  s), and f = frequency. Electrons can have only certain discrete energies, not energies in between.

9-1. The Photoelectron Effect The photoelectric effect is the emission of electrons from a metal surface when light shines on it. The discovery of the photoelectric effect could not be explained by the electromagnetic theory of light. Albert Einstein developed the quantum theory of light in 1905.

9-2. Photons Einstein expanded Planck's hypothesis by proposing that light could travel through space as quanta of energy called photons. Einstein's equation for the photoelectric effect is hf = KE + w. Although photons have no mass and travel with the speed of light, they have most of the other properties of particles. The higher the frequency (or shorter the wavelength) the higher the energy. Albert Einstein ( )

9-3. What is light? Light exhibits either wave characteristics or particle (photon) characteristics, but never both at the same time. The wave theory of light and the quantum theory of light are both needed to explain the nature of light and therefore complement each other.

9-4. X-rays Wilhelm Roentgen accidentally discovered x-rays in In 1912, Max von Laue showed that x-rays are extremely high frequency EM waves. X-rays are produced by high energy electrons that are stopped suddenly; the electron KE is transformed into photon energy. Wilhelm Roentgen ( )

9-5. De Broglie Waves In 1924, the French physicist Louis de Broglie proposed that moving objects behave like waves; these are called matter waves. The de Broglie wavelength of a particle of mass m and speed v is = h / mv. Louis de Broglie( ) 1924 – Nobel Prize in 1929

An 18-wheeler moving down Hwy 99 at 60mph has a wavelength smaller than an atom. However, an electron (very light) moves much faster and its wavelength is much larger than its size.

9-5. De Broglie Waves An electron Microscope and a micrograph of bacteriophage viruses approximately 1 μm across.

9-6. Waves of What? The quantity that varies in a matter wave is called the wave function (  ). The square of the wave function (  2 ) is called the probability density. For a given object, the greater the probability density at a certain time and place, the greater the likelihood of finding the object there at that time. The de Broglie waves of a moving object are in the form of a group, or packet, of waves that travel with the same speed as the object.

9-7. The Uncertainty Principle The uncertainty principle states that it is impossible to know both the exact position and momentum of a particle at the same time. The discoverer of the uncertainty principle was Werner Heisenberg. The position and motion of any object at a given time can only be expressed as probabilities. Werner Heisenberg ( )

9-8. Atomic Spectra A spectroscope is an instrument that disperses the light emitted by an excited gas into the different frequencies the light contains. Light with multiple wavelengths Wavelengths separated refraction

9-8. Atomic Spectra An emission spectrum consists of the various frequencies of light given off by an excited substance. Below is the part of the emission spectra of sodium.

Emission Line Spectra of Some Common Elements

9-8. Atomic Spectra An absorption spectrum consists of the various frequencies absorbed by a substance when white light is passed through it. The frequencies in the spectrum of an element fall into sets called spectral series. Seen here is the spectral series of hydrogen.

9-9. The Bohr Model The Niels Bohr model of the atom, proposed in 1913, suggested that an electron in an atom possesses a specific energy level that is dependent on the orbit it is in. An electron in the innermost orbit has the least energy. He predicted that the distance from the proton to the electron in a hydrogen atom was about 0.89Å. Niels Bohr ( )

9-9. The Bohr Model Electron orbits are identified by a quantum number n, and each orbit corresponds to a specific energy level of the atom. An atom having the lowest possible energy is in its ground state; an atom that has absorbed energy is in an excited state.

9-10. Electron Waves and Orbits When an electron "jumps" from one orbit (energy level) to another, the difference in energy between the two orbits is hf, where h is Planck’s constant and f is the frequency of the emitted or absorbed light.

Origin of Absorption Spectra

9-10. Electron Waves and Orbits An electron can circle a nucleus only in orbits that contain a whole number of de Broglie Wavelengths. The quantum number n of an orbit is the number of electron waves that fit into the orbit.

9-10. Electron Waves and Orbits Electrons seemed to be locked into these wave patterns around the nucleus.

9-11. The Laser The word laser comes from light amplification by stimulated emission of radiation.

9-11. The Laser Excitation Methods include electrical charge, light (below), and chemical reaction.

9-11. The Laser Lasers are used in light shows and eye surgery.

9-11. The Laser Holograms are made from laser light without using an image forming device. The image formed becomes 3D.

Holograms 3D pictures made by Lasers using the interference pattern between reflected laser light from the surface of an object and the undisturbed laser light reflected from a mirror. The Interference pattern is recorded on film. The developed film can then be used by a laser to recreate the image in 3D

30 Holograms are made from laser light without using an image forming device. Tupac holographic concert and a holographic fashion display. Holograms

9-11. The Laser Holograms are made from laser light without using an image forming device. The image formed becomes 3D. Meet Mika…..(Artoolkit)

9-12. Quantum Mechanics The theory of quantum mechanics was developed by Erwin Schrödinger, Werner. According to quantum mechanics, the position and momentum of a particle cannot both be accurately known at the same time. Only its most probable position or momentum can be determined. The most probable distance between the proton and electron for a hydrogen atom turns out to be about 0.89Å, the same as Niels Bohr. 0.89Å Erwin Schrödinger ( )

9-13. Quantum Numbers 1. The principal quantum number n governs the electron's energy and average distance from the nucleus. 2. The orbital quantum number l determines the magnitude of an atomic electron's angular momentum. 3. The magnetic quantum number m l specifies the direction of an atomic electron's angular momentum. 4. The spin magnetic quantum number m s of an atomic electron has two possible values, +1/2 or -1/2, depending on whether the electron aligns itself along a magnetic field (+1/2) or opposite to the field (-1/2).

9-13. Quantum Numbers principal quantum number n 1,2,3,….. orbital quantum number l 0,1,2,….n-1 magnetic quantum number m -l to +l for n=2 -2,-1,0,1,2 spin magnetic quantum number +½ or –½ spin Its like your address. To find where you are you need to know 4 things: state, city, street, house #. To know where or what state the electron is in you need to know the four quantum numbers.

Quantum #’s are like an Address. What do you need to know to find out where you live? State CityStreetHouse Principle Quantum # (n) Angular Quantum # ( l) Magnetic Quantum # (m l ) Spin Quantum # (m s )

1s3s2s 2px 3pz 3d 2py 2pz 3py 3px Quantum Numbers

The outside of the2s orbital can be seen below. The 2p orbital is in the middle. A combination of the 3 2p orbitals is shown in the movie on the right. Movie

Scanning Tunneling Microscope

Scanning Tunneling Microscope Electron Clouds Image Movie

9-14. The Exclusion Principle The exclusion principle, first proposed by Wolfgang Pauli in 1925, states that only one electron in an atom can exist in a given quantum state. Each atomic electron must have a different set of quantum numbers n, l, m l, and m s.

Fig Magnetic resonance imaging (MRI) is a method of mapping tissue density based on proton spin that shows the nature of soft tissue better than x-rays.