Atomic Physics – Chapter 9
development of physics before 1900
development of physics after 1900
to do with the electrons in an atom
elements would get to a point where they couldn’t be divided anymore (true)
idea of continuous matter
you can keep dividing elements forever and ever – Aristotle
disproved continuous matter, proved discrete matter
used billard ball model (1807)
electron discovered in
revised Dalton’s model – plum pudding model
how’d Thompson discover the electron?
studied electrical discharge of low pressure gas tubes and found that when high voltage applied to tube, ray was produced and it sped from negative electrode to positive electrode – concluded it was a stream of negatively charged particles, the electron
discovered the nucleus
how is visible light emitted?
by atoms of a glowing hot solid (incandescent)
how does the temperature of a solid affect its atoms
the hotter the solid, the greater the electron vibrates, and the emitted radiation has a higher frequency
when frequencies higher than visible light don’t have a high enough intensity according to classical theory
how did Planck explain the ultraviolet catastrophe?
said energy is quantized, aka an oscillator can only have specific amounts of energy
what is a quantum?
a “packet” of energy
electrons are emitted when certain metals are exposed to light – a direct conversion of light into electrical energy. couldn’t be fully explained by classical theory
how couldn’t the photoelectric effect be explained?
in theory light explained a wave, and it would take wave way too long to give energy needed for electron to be emitted when electrons are emitted immediately
also light needed to be above certain frequency to emit electron when by theory any frequency of light should be able to emit electron
how did Einstein solve the problem of the photoelectric effect?
applied Planck’s constant and decided light is quantized and called each quantum a photon – the higher the frequency of light, the higher the energy
dual nature of light
light described as a wave and as a particle
not continuous spectrum, breaks between the colors
line emission spectra
when light from gas discharge tube analyzed with spectrometer – only spectral lines from certain frequencies are observed – result of quantum effect
line absorption spectra
when visible light of all wavelengths passed through gaseous element before entering spectrometer – result of quantum effect
explain bohr’s theory and hypothesis
bohr assumed one electron revolves around nuclear proton in circular orbit
assumed angular momentum of electron quantized
hydrogen electron could only exist in certain orbits with certain radii
how did classical theory interfere with bohr’s claim that electron didn’t radiate energy when in orbit, only when making transition from one orbit to another
according to classical theory accelerating electrons radiate E-M energy and when electron’s in orbit, it continuously has acceleration so should always radiate energy
allowed orbits for hydrogen
energy’s needed to (inside of atom pertaining to energy levels)
lift electron to a higher level
the lowest energy state of an atom, n=1
if an electron is given energy it moves from n=1 to
n=2, 3, 4 – the excited states
when is an electron ionized?
when it gains energy, moves out of ground state
transitions to a particular lower level
transitions from n= 3, 4, 5, 6 down to n=2
how can you find the composition of distant stars?
by looking at the analysis of the dark absorption lines in their spectra
the study of spectra and energy levels of molecules
how does a microwave work?
the moisture in the food absorbs the microwaves and the electrons gain energy and rotate more rapidly, so the food is heated and cooked
high frequency, high electromagnetic radiation
discovered the x-ray (1895)
how do x-rays work?
electrons accelerated through large electrical voltage toward a metal target and when electrons hit the target, electrical repulsions decelerate the incident electrons – results in the emission of high frequency x-ray photons
light amplification by stimulated emission of radiation
when electron excited by photon, emits the photon, and immediately goes back to ground state
metastable excited states
electron can jump into excited state and can remain there briefly
when many atoms excited into metastable state by imput of appropriate energy – occasionally excited atom stimulated to emit proton
excited atom struck by photon of the same energy as the allowed transition and photons emitted – 2 photons emitted
laser pointer – how it works
the result of many stimulated emissions and reflections in laster tube is a narrow intense beam of laser light
photons having same energy and wavelength
traveling in phase in the same direction
when light consists of many wavelengths and excitation occurs randomly
is there a limit to the accuracy of a measurement?
according to classical theory, no, but quantum theory sets limits on accuracy of a measurement
there is a limit on measurement of accuracy, but only important when dealing with particles of atomic/subatomic size
Heisenberg’s uncertainty principal
(1927) Wemer Heisenberg, it is impossible to know exactly both the velocity and the position of a particle at the same time
If waves can behave like particles then particles can behave like waves – any moving particle has a wave associated with it
in deBroglie’s hypothesis, did he think that the smaller mass would have a shorter or longer wavelength?
uses beam of electrons to view objects/light
new kind of physics, came about because of discovery of the dual nature of light and matter. Study of physics at the atomic level where energy is quantized in discrete, rather than continuous, levels.
what does Schrodinger’s electron/quantum cloud model of atom focus on and why are there only certain energy levels an electron can occupy?
the wave nature of electron and treats it as a spread out wave, its energy levels being the consequence of the wave having to have a whole number of wave lengths to form standing waves in orbits around nucleus – this explains the quantization of energy with electrons
how does Schrodinger’s model explain quantinization
standing waves don’t have to move one place to another so electron in standing wave not accelerating and wouldn’t have to radiate energy