Chapter 7 Flashcards
how has much of our understanding of the electronic structure of atoms came to be
as a result of the analysis of light emitted or absorbed by substances
what did Sir Isaac Newton discover about white light
that it can be broken down into components with different colors from red to violet by the action of a prism
properties of waves (maxwell)
suggested that light consists of “waves” and that the energy is spread over space like an oscillating liquid
amplitude
the max displacement (height of wave above the centerline)
wavelength
represented by lamda, is the peak-to-peak distance
frequency
represented by nu, the number of wavelengths that pass a given point in 1 second
units of frequency
are cycles per second (s-1) or hertz (Hz)
c
the speed of light (product of wavelength + frequency)
- speed of a light wave in a vacuum is constant
- c=3x10^8 ms-1
how are wavelength and frequency related
wavelength and frequency are inversly related
electromagnetic waves
all visible light consists of electromagnetic waves
- there are oscillating electric and magnetic fields
- these fields are perpendicular to the direction of the light
equation for electromagnetic radiation
c=(lamda)(nu)
electromagnetic spectrum
electromagnetic radiation has a large range of wavelengths and frequencies with no known limit
blue light
has a smaller wavelength but a smaller frequency
black body radiation
as a body is heated, it glows more brightly and the color of light it gives off changes from red through orange and yellow to white
incandescence
rhe emission of light (visible electromagnetic radiation) from a hot body due to its temperature
how did planck describe black body radiation
- it is not possible to put any arbitrary amount of energy into an oscillator, the energy must be quantized
- oscillator must gain and lose energy in “packets” or “quanta” of magnitude (hv) where h is plancks constant (6.63x10^-34
plancks constant
6.63x10^-34
oscillator
a machine that generated oscillating electric currents and voltages by nonchemical means
classical oscillator
has continuous valves of energy and can gain or lose energy in arbitrary amounts
formula for an oscillating atom releasing energy
E=hv
quantum oscillator
has discrete energy levels and can only gain or lose energy in discrete energy levels and can only gain or lose energy in discrete amounts
Heinrich Hertz
showed that electrons are ejected from a metal when it is exposed to ultraviolet radiation
photoelectric effect
- if radiation frequency is less than the threshold value (Vo) of the metal, than no electrons are emitted no matter how intense
- if radiation frequency is greater than or equal to the threshold value (Vo) than electrons are emitted
- if increase intensity of light (more pockets of light) more electrons are emitted but there is no change to the max kinetic energy of the electron
Albert Einstein’s statements on light ect
- light is quantizes as photons
- light has properties of both waves and matter
- neither the wave nor the particle view alone is a complete description of light (particle-wave duality of light)
particle-wave duality of light
neither the wave nor the particle view alone is a complete description of light
threshold value
a point in which a change is executed
can white light be seperated
yes, by a prism. and this produces a continuous range of colors which merge together
discharge tube
tube with a low pressure of gas, to which a high voltage is applied
what happens when light is emitted from a gas in a discharge tube
the light is seperated by a prism but a continuous spectrum of colors is not observed and the spectrum consists of lines
assumptions of the Bohr Model of the Atom
- the electron moves in circular orbits about the nucleus with motion described by classical physics
- only a fixed set of orbits are allowed and in these orbits, no energy is emitted (no death spiral) (electron falling into the nucleus)
history of the principal quantum number (n)
bohrs theory gave the energies of these orbits as a function of a principal quantum number
can electrons pass from one orbit to another
yes and when electrons pass from one orbit to another it is accompanied by discrete changes in energy (light is emitted or absorbed)
why was the Bohr atom important
because it introduced the idea of quantized energy states for electrons in atoms
3 shortcomings of Bohrs model of the atom
- it cannot predict the energy levels and spectra of atoms and ions with more than one electron
- it violates the heinsenberg uncertainty principle in that both position and momentum cannot be known exactly at the same time
- bohrs theory was replaced by modern quantum mechanics in 1926
behavior of electromagnetic radition as told by Einstein
suggested that electromagnetic radiation would behave like particles (photons) and eject electrons from a metal surface (photoelectric effect)
but
electromagnetic radiation also behaves like waves
diffraction pattern
when 2 light waves interfere with eachother and may interfere constructively giving a bright line or destructively giving a dark region
who proposed wave-particle duality
Louis de Broglie made a revolutionary proposition, saying that small particles of matter may at times display wave-like properties
history of the circular standing wave
deBroglie recognized that the standing waves are examples of quantization and suggested that the electron in a Bohr orbit may be associated with a circular standing wave
standing wave
also known as a stationary wave, is a wave which oscillates in time but whose peak amplitude does not move in space.
circular standing wave
superimpose a sine wave on the radius r of your circle
what 2 famous equations did de Broglie link to make his own equation
Einstein and Plancks, to show the relationship between the wavelength and momentum of the photon
Louis de Broglie’s nobel prize
(1929) for his discovery of the wave nature of electrons and light=matter
when are the wave properties of matter apparent
only for the very small masses of matter (electrons)
Heisenberg’s Uncertainty Principle concluded . . .
-the wave-particle duality places a fundamental limitation on how precisely we can know the location and momentum of any object at the same instant in time
why is the uncertainty principle important
because when the masses are as small as an electron. if not, the particles become fuzzy and cannot be localized`
the schrodinger equation
wrote an equation that describes both the particle and wave nature of an electron (can only be used for the hydrogen atom)
are there limits to wave function?
no, it stretches out to infinity so an atom has no boundaries
boundaries of an atom
inside the “boundaries” of an atom, the electron has a specific probability of being located (typically 99%)
the value of wave function is greatest . . .
nearest the nucleus, but rapidly decreases thereafter (never goes to zero tho)
the probability of finding an electron in a shell is greatest
at some distance from the nucleus. this is the same difference that is calculated by Bohr for an electron orbit in his model
atomic orbital
the wave function for an electron, it is described by 3 quantum numbers - n,l,m
-describes a region in space with a definite shape where there is a high probability of finding the electron
n
principal quantum number (distance from nucleus)
l
angular movement quantum number (shape of orbital)
m1
magnetic quantum number (orientation of the orbital0
4th quantum number
refers to the magnetic property of electrons
ms=spin quantum number
principal quantum number (n)
- quantum number in which the energy of an electron in an atom primarily depends
- can have any positive value (1,2,3)
the smaller the value of n
the lower the energy and the smaller the orbital
orbitals with the same value for n
are said to be in the same shell (distance of e- from the nucleus)
schrodinger equation
psi(wavefunction)= fn (n,l,m1)
angular momentum quantum number (l)
distinguishes orbitals of a given shell, having different shapes
-shape of the volume of space that the electron occupies
for every given value of n, l=
n-1
l for n=1,2,3
=0 (s orbital)https://www.brainscape.com/decks/9348203/cards/quick?pack_id=16236168#
=1 (p orbital)
=2 (d orbital)
why are orbitals labeled s,p,d,f
sharp, principal, diffuse, fundamentals (some poor darn fool)
s orbital shape
spherical
p orbital shape
has 2 lobes along a straight line through the nucleus, one lobe on either side
d orbital shape
clover-shaped
magnetic quantum number, m1
distinguishes orbitals of a given n and l, that is, of a given energy and shape but having different orientations
- in each 1=1 subshell there are 3 p orbitals corresponding to m1=+1,0,-1
- in each 1=2 subshell there are 5 d orbitals corresponding to m1=-2,-1,0,1,2
spin quantum number, ms
refers to the 2 possible orientations of the spin axis of an electron
-ms=+1/2 or -1/2
what does energy depend on in a single electron atom
energy only depends on principal quantum number n (En=-RH(1/n^2)
