3 1 Schrodinger s Cat 3 2 The Nature of Light Wave Nature of Light The Quantum Mechanical Model of the Atom Chemistry 131 Chapter 3 Electrons are the smallest particles that make up matter The absolutely small quantum world of the electron behaves differently than the large macroscopic world we observe When unobserved quantum particles like electrons can be in two different states at the same time Quantum Mechanical model of the atom describes electrons as they exist within atoms Light has many characteristics in common with electrons such as wave particle duality certain properties of light as best described as a wave or particle Light is electromagnetic radiation energy embodied in oscillating electric and magnetic fields Magnetic Field a region of space where a magnetic particle experiences a force space around magnet Electric Field region of space where an electrically charged particle experiences a force proton has electric field around it Speed of light c 3 00 10 m s Speed of sound 340 m s A wave is characterized by its amplitude and wavelength Amplitude vertical height of a crest determines light s intensity brightness Wavelength distance between crests determines color Light is also characterized by its frequency the number of cycles wave crests in a given time period cycle s Hz Frequency is inversely proportional to the wavelength Formula The different colors in visible light light seen by the human eye corresponds to the different wavelengths frequencies Electromagnetic spectrum is a chart of all the wavelengths of electromagnetic radiation Gamma Rays Shortest wavelength 10 m Produced by sun stars unstable atomic nuclei Dangerous to humans damage biological molecules The Electromagnetic Spectrum Ultraviolet UV Radiation X rays Wavelength 10nm Used to image bones and internal organs Can be dangerous in over exposure Wavelength 400nm 10nm Component of sunlight that produces sunburn tan Excessive exposure can cause skin cancer Visible Light Wavelength 750 400nm Involves all the colors we can see the rainbow Is not damaging to humans Infrared IR Radiation Wavelength 1mm 750nm Heat felt when near hot object Can be detected in infrared sensors night vision Microwaves Wavelength 187mm 1mm Used for radar and microwaves Absorbed by water and heats substances containing water Radiowaves Wavelength 600m 187mm Longest wavelength Produce radio all phones tv Interference and Diffraction Waves interact with each other through interference cancelling each other out or building each other up depending on alignment 1 Constructive interference When two waves of equal amplitude are in phase when they interact Align with overlapping crests double amplitude 2 Destructive interference When two waves are out of phase when they interact Align with crest from one overlaps trough of the other Waves also exhibit diffraction when a wave encounters an obstacle or slit that is comparable in size to its wavelength it bends diffracts around it An interference pattern is the diffraction of light through two slits separated by a distance comparable to the wavelength of the light The Particle Nature of Light The photoelectric effect is the observation that many metals emit electrons when light shines upon them This can be measured as an electrical current Atomic Spectra 3 3 Atomic Spectroscopy and the Bohr Model Binding energy is the energy with which the electron is bound to the metal High frequency low intensity light produces electrons without lag time The amount of energy E depends on frequency E h h is Planck s constant 6 626 10 Js A packet of light is called a photon or a quantum of light Energy can also be expressed as E For an electron bound to the metal with binding energy the threshold frequency is reached when energy of photon Threshold Frequency Condition h As the frequency of the light increases over the threshold frequency the excess energy of the photon transfers to electron as kinetic energy KE h Atomic spectroscopy is the study of the electromagnetic radiation absorbed and emitted by atoms When an atom absorbs energy heat light electricity it often re emits that energy as light Light emitted by various atoms contain distinct wavelengths Passing light emitted by a single element through a prism results in a series of bright lines called emission spectrum The emission spectrum is specific to each element and can be used to identify them The Rydberg equation predicts the wavelength of emission spectrum 1 1 097 10 1 1 Rydberg Constant Integers Electrons travel around nucleus in specific fixed circular distances from nucleus Energy of each orbit is also fixed quantized No radiation is emitted by electron in stationary state When electron jumps transitions from one state to another radiation is emitted or absorbed Electron is never absorbed between states only in one or another The Bohr Model was not fully accepted eventually replaced The presence of intense lines in the spectra of a number of metals is the basis for flame tests simple tests used to identify elements in ionic compounds The emission of light from elements is easier to detect the absorption of light by elements is more commonly used The Bohr Model Stationary States Atomic Spectroscopy and the Identifications of Elements m n can also be written as final and initial for stages of electron 2 The Uncertainty Principle single electrons interfering with themselves 3 4 The Wave Nature of Matter Absorption spectrum is dark lines on a bright background Measured by passing white light through a sample and observing what wavelengths are missing due to absorption Plots the intensity of absorption as a function of wavelength The wave nature of electrons replaced Bohr s Model The wave nature of the electron is seen most clearly in diffraction The interface patter is not caused by pairs of electrons interfering with each other but by The wave nature of electrons is an inherent property of individual electrons Three Important Manifestations of Electron Wave Nature 1 The de Broglie Wavelength A single electron has wave nature its wavelength is related to its kinetic energy fast electron high kinetic energy short wavelength The wavelength of an electron of mass m moving at velocity is v the de Broglie relation We can never both see the interference pattern and simultaneously determine which hole the electron goes through cannot see wave nature particle nature simultaneously Wave nature particle nature of electrons are complimentary properties