Chapter 6 Flashcards
Wavelength (lambda)
Distance between two peaks (or two troughs)
Frequency (nu)
Number of peaks to pass a given point per second
Speed of light (c)
c = 3.00 • 10^8 m/s
Speed of light equation
c = (nu)(lambda)
As energy increases, wavelength __________ and frequency ____________
Wavelength decrease and frequency increases
General order of the different types of radiation going from highest to lowest energy
Gamma, x-ray, ultraviolet, infrared, microwave, broadcast and wireless radio
Angstrom (A with °)
10^-10 m, x-ray
Nanometer (nm)
10^-9, ultraviolet
Micrometer (um)
10^-6, infrared
Millimeter (mm)
10^-3, microwave
Centimeter (cm)
10^-2, microwave
Meter
1 m, television, radio
Kilometer (km)
10^3 m, radio
Blackbody radiation
When the temperature of an object increases, it emits electromagnetic radiation of shorter and shorter wavelength, so higher and higher frequency
Energy of 1 photon of light equation
E = h(nu)
E = (h • c)/(lambda)
Planck’s constant
h = 6.626 • 10^-34 J•s
Photoelectric effect
Light shining on a clean metal surface causes electrons to be emitted but only if the energy of the incoming light is above the work function of the metal
What happens if a lot of photons strike the metal (increase the intensity)?
A lot of electrons are also ejected, but only if the photons possess enough energy to overcome work function
What happens if higher energy photons (above the work function of metal) strike the metal?
The ejected electrons have greater kinetic energy due to conservation of energy
Work function equation
E photon = (phi) metal + E k,electron
We see different line spectra for different…
Elements
Rydberg equation (line spectrum for hydrogen only)
1/(lambda) = (Rh)(1/((n1)^2 - (n2)^2))
Rh = 1.096776 • 10^7 m^-1
n1 and n2 are positive integers
Bohr’s 1st postulate
Only orbits of certain radii, corresponding to certain specific energies, are permitted for the electron in a hydrogen atom
Electronic energy levels in the hydrogen atom equation
E = (-hc(Rh))(1/n^2) = (-2.18 • 10^-18 J)(1/n^2)
n = principal quantum number (1, 2, 3, etc.)
Why does energy of level increase (become more positive) as n increases?
Distance of electrons (-) from nucleus (+) increase, creating a greater potential energy
Why are all of the energies negative values?
Attraction + and - charges
What do you think the energy of electron is at an n=infinity?
Distance would go to infinity, so potential energy would get less and less negative, making it equal zero
As the principal quantum number, n, increases for the hydrogen atom…
The energy levels converge (get closer and closer together)
Bohr’s 2nd postulate
An electron in a permitted orbit is in an “allowed” energy stare. An electron in an allowed energy state does not radiate energy, and therefore does not spiral into the nucleus.
Bohr’s 3rd postulate
Energy is emitted (n decreases) or absorbed (n increases) by the atom only when the electron changes from one allowed energy state to another. This energy us emitted of absorbed as a photon.
If we let white light (photons with different energies) interact with the hydrogen atom…
When a photon strikes the electron with the right energy that matches the difference between energy levels, then that photon is absorbed and the electron is promoted to a higher energy level
Equation to calculate light involved in a transition
Delta E = Ef - Ei = (-2.18 • 10^-18 J)(1/((nf)^2 - 1/(ni)^2))
Light is involved ONLY…
When an electron undergoes a transition between energy levels
If a hydrogen atom absorbs a photon
n increases, change in energy of the atom is positive
If a hydrogen atom emits a photon
n decrease, change in energy of the atom is negative
de Broglie wavelength equation
Lambda = h/(m • nu)
Constructive interference
The amplitude of two waves is added
Destructive interference
The amplitude of two waves is subtracted
Heisenberg’s uncertainty principle equation
(Delta x)(delta m•nu) >= h/(4pi)
de Broglie and matter waves
An electron can behave like a wave and a particle
Heisenberg and the uncertainty principle
It is impossible to precisely know two measured values at the same time. The energy will be quantized and precisely known, so the position is described in terms of probability
