•Niels Bohr in 1913 proposed a quantum model for the
hydrogen atom which correctly predicted the frequencies of
the lines (colors) in hydrogen’s atomic emissions spectrum.
•His model gave atoms only certain allowable energy
states.
•The lowest state is called the ground state.
•When an atom gains energy it is said to be in an excited
state.
• When elements are given energy from a variety of sources
(heat, light, electricity) the electrons absorb that energy,
& jump up to a higher energy level, the excited state. The
electrons can return to ground state by giving off the energy
as a color of light, called photons of light.
•Each element gives off a unique color called its
atomic emission spectrum. The electrons are what give
each element their unique color.
•Light gives us a clue to how electrons are arranged. Light
behaves like a wave & like a particle.
•wave particle duality of nature – everything in the
universe has properties of both waves and particles
(ex. Duality of good vs. evil in man)
Light in wave form is called an electromagnetic wave
and is part of the electromagnetic spectrum which includes
x-rays, TV waves, microwaves, radio waves, UV waves &
gamma rays.
Trough – low points
Crest – high points
Amplitude – max displacement from equilibrium (middle of
wave).
Wavelength – the shortest distance between points in which
a wave repeats itself. (crest to crest or trough to trough)
symbol - λ
Rope demo
Parts of a Wave
length
•Wavelength crest to a crest or trough to a trough
lambda
•Symbol = λ (
)
•Measured in meters
of one wave, from a
•Frequency- number of waves that pass a point in 1 second
•symbol = f or v ( nu
)
•Measured in
Hertz
(Hz) or 1/s, s-1
•All EM radiation travels at the speed of light, c = 3.00 x 108m/s
in the vacuum of space
Formula: c = λ v
or Formula: c = λ f
c is constant speed of light
ν or f is frequency
λ is wavelength
Ex. 1) Light in the middle of the ultraviolet region of the
electromagnetic radiation spectrum has a frequency of
2.73x1016s-1. Find the UV light’s wavelength.
Ex. 2) Yellow light has a wavelength of 5.70x10-7m.
Calculate the frequency of the yellow light.
•Light as a particle is called a photon.
•Light is like a particle because there are only certain amounts
of energy it can have.
•The minimum amount of energy a photon can have is called a
quantum.
•Max Planck found that this energy could be calculated with
the formula
E = h ν or E = h f
•E is energy, measured in Joules (J)
•h is Planck’s Constant = 6.626 x 10-34 Js
•v or f is frequency (Hz or 1/s or s-1) same
frequency as earlier
•Once the minimum amount of energy is calculated, the actual
energy can be a multiple of the quantum amount. (1x E, or 2
x E, or 3 x E....)
Ex. 3 From examples 1 and 2, we have the frequency of
UV light as 2.73x1016s-1 and the frequency of yellow light
as 5.26x1014Hz. Calculate the energy in joules, of an
individual photon of each.
Ex. 3 From examples 1 and 2, we have the frequency of
UV light as 2.73x1016s-1 and the frequency of yellow light
as 5.26x1014Hz. Calculate the energy in joules, of an
individual photon of each.
UV light
(6.626x10-34Js)(2.73x1016s-1) =1.81x10-17J
yellow light (6.626x10-34Js)(5.26x1014s-1) =3.49x10-19J
Which has more energy? UV light or yellow light?
Ex. 3 From examples 1 and 2, we have the frequency of
UV light as 2.73x1016s-1 and the frequency of yellow light
as 5.26x1014Hz. Calculate the energy in joules, of an
individual photon of each.
UV light
(6.626x10-34Js)(2.73x1016s-1) =1.81x10-17J
yellow light (6.626x10-34Js)(5.26x1014s-1) =3.49x10-19J
Comparing the two, UV light has more energy than
yellow light
•Electrons (called photoelectrons) are emitted from a metal’s
surface when light of a certain frequency shines on the
surface.
•Example: calculators.
•Photoelectric cells convert light into electric energy
In Summary
c = λ f or c = λ v
c = speed of light = 3.00 x 108 m/s
f (or v) = frequency = Hz, 1/s, s-1
λ = wavelength = m
E = h f (or E = h ν )
E = Energy = J
h = Planck’s Constant = 6.626 x 10-34 Js
Water drops in the air disperse the white light of the sun
into a rainbow. What is the energy of a photon from the
violet portion of the rainbow if it has a frequency of 7.23
x 1014 Hz?