CH 2.1-2.5 Flashcards
Henry Moseley
Found that protons identify the atom, not the atomic mass
- Used X-ray scattering & built an instrument to measure the charge of the nucleus & confirm the existence of electrons
- looked at the pattern of the wavelengths, tried to plot it linearly but then plotted the square root of the frequency (it was linear)
- Concluded that the atomic # = + charge on nucleus
- ordered 92 elements
Equation for speed of light
Speed of light (cycles) = wavelength (meters) x frequency (cycles per second, hertz)
The wave nature of light
- electromagnetic waves originate form the movement of electric charges
- movement produces fluctuations in electric & magnetic fields
- electromagnetic waves require no medium
- electromagnetic radiation is characterized by its wavelength, frequency, & amplitude
Wavelength
Distance btwn 2 peaks or troughs in a wave (consecutive cycles)
Frequency
Points to the number of waves (cycles) per second that pass a given point in space
- Unit = waves/s or s^-1 (hertz)
Speed
Constant, height of wave
- Speed of light = 2.9979 x 10^8
Amplitude
- Indicates field strength
Standing waves
Stationary (waves don’t travel along the length of the string) waves moving up & down
- The electron in the hydrogen atom is considered to be a standing wave
- Like musical instruments
What is the relationship between wavelength & frequency?
They are inverses of each other
- increase in frequency = decrease in wavelength & vice versa
James Clerk Maxwell
- predicated the existence of invisible “light” waves
- Radio waves reflect & refract just like light
- light travels @ a constant speed
- Paradigm: light is an electromagnetic wave
Heinrich Hertz
- detected radio waves
Refract
Going through different mediums
Diffract
Waves spread out when they encounter an obstacle about the size of the wavelength
- produces constructive & destructive interference
Who showed that light could be diffracted
Thomas Young
Colors in order from shortest wavelength to longest
VBGYOR
Types of waves in order of least to greatest wavelengths
Gamma rays
X rays
Ultraviolet
Infrared
Microwave
Radio
Isaac Newton
- Law of Gravitation
Black body
An ideal object that absorbs all incident EM radiation, regardless of frequency or angle of incidence (can also emit radiation- continuous spectra)
- as it is heated, it glows more brightly, giving changes from red through orange & yellow toward white as it gets hotter
- doesn’t favor one wavelength over the other
- Colors correspond to the range of wavelengths radiated by the body at a given temp
Stefan-Boltzmann Law
Total intensity of radiation emitted by a black body over all wavelengths proportional to T^4
- based on experimental measurements by Tyndall
Ultraviolet Catastrophe
EM Paradigm. Cannot explain the wavelength dependence of the intensity of the light that is emitted from a simple heated object
Max Planck
Explains the ultraviolet catastrophe by quantizing the energy of light
- E = hv
- proposed that exchange of energy btwn matter & radiation occurs in packets of energy called QUANTA
- h = Planck’s constant 6.626 x 10^-34 Jxs
- Radiation of frequency (v = E/h) is emitted only if enough energy is available
- energy can only be gained or lost only in whole-number multiples of hv
- implies that energy has particulate properties
- concept completely disregarded classical physics
Change in energy equation
Delta E= nhv
- n is an integer
- h is Planck’s constant
- v represents the frequency of EM radiation
Quanta
Discrete amount of energy
The photoelectric effect
The phenomenon whereby electrons are emitted from the surface of a metal when light strikes it
- No electrons emitted by any given metal below a specified threshold frequency, v0
- When v is LESS than v0, no electrons are emitted, regardless of the intensity of light
- When v is GREATER than v0, the # of electrons increases with the intensity of light
- When v is GREATER than v0, the kinetic energy of emitted electrons increases linearly with the frequency of the light
- The current of photoelectrons, when it exists, is proportional to the intensity of the light falling on the surface
- The energy of the photoelectrons emitted is independent of the light intensity but varies linearly with the light frequency
- facts cannot be explained within framework of classical physics
Electromagnetic radiation
Radiant energy that exhibits wavelike behavior & travels through space at the speed of light in a vacuum
Three primary characteristics of waves
wavelength, frequency, speed
Particles
Things that had mass & whose position in space could be specified
Waves
Massless & delocalized
What did scientists believe about particles & light before the 1900s?
There was no intermingling of matter & light
Quantum
Small “packets” of energy that is quantized in units of hv
Photon
A quantum of electromagnetic radiation
Albert Einstein
Suggested that electromagnetic radiation can be viewed as a stream of “particles” called photons
- Special Theory of Relativity; E=mc^2; states that energy has mass
- Proposed that light of fixed frequency (v) consists of a collection of indivisible discrete units called quanta
- applied Planck’s quantum theory (photos)
Kinetic energy of electron equation
KE = 1/2mv^2 = hv - hv0
- m= mass of electron
- v= velocity of electron
- nu=energy of incident photon
- hv0= energy required to remove electron from metal’s surface
Energy of photon equation
Energy of photon = hc/wavelength
Apparent mass of a photon of light equation
m = E/c^2 = (hc/wavelength)/c^2 = h/(wavelength x c)
Dual nature of light
The statement that light exhibits both wave & particulate properties
De Brogile’s equation
wavelength = h/(m x v)
- h = Planck’s constant
- m = mass
- v = velocity of particle
- calculate wavelength for a particle
Constructive diffraction
Scattered light produces a bright area
- peaks & troughs of the beams are in phase