•Rutherford’s model
-Shows where protons & neutrons are
-Not good at showing the location of electrons
•When elements are heated, they are excited
& jump up to a higher energy level. In doing so, they give off a
color 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.
•Light in wave form is called an electromagnetic
wave, & is part of the electromagnetic spectrum which
includes x-rays, TV waves, microwaves, radio waves, UV
waves & gamma waves.
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
Parts of a Wave
length
•Wavelength crest to a crest or trough to a trough
lambda
•Symbol = λ (
)
meters
•Measured in
of one wave, from a
•Frequency- number of waves that pass a point in 1 second
•symbol = v (
)
nu
•Measured in
Hertz
(Hz)
•All EM radiation travels at the speed of light, c = 3.00 x 108
m/s in the vacuum of space
•Formula: c = λ v
c is constant speed of light
v is frequency
λ is wavelength
Microwaves are used to transmit information. What is the
wavelength of a microwave having a frequency of 3.44 x
109 Hz?
Known
Unknown
v= 3.44 x 109 Hz
c = 3.00 x 108 m/s
λ= ? m
c = λv
λ= c/v
• λ= 3.00x
8
10 /
3.44 x
• Answer: 8.72 x
9
10
-2
10 m
What is the frequency of green light, which has
a wavelength of 4.90 x 10-7m
An X ray has a wavelength of 1.15 x 10-10m.
What is the frequency?
•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=hν
•E is energy, measured in Joules (J)
•h is Planck’s Constant = 6.626 x 10-34 Js
•v is frequency (Hz or 1/s)
•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....)
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 1014Hz?
Known
v = 7.23 x 1014 s-1
Unknown
Ephoton = ? J
h = 6.626 x 10-34 J s
Ephoton= (6.626 x 10-34J s)(7.23 x 1014 s-1)
• Cancel the units
• Answer: 4.79 x 10-19J
What is the energy of each of the following
types of radiation?
a. 6.32 x
20
-1
10 s
b. 9.50 x 10 13 Hz
c. 1.05 x 10 16 s-1
•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
•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.
•Bohr also said that the motion of the electron
relates to its energy state. That electrons
move around the nucleus in certain allowed
circular orbits.
•The smaller the orbit, the lower the energy state.
•Bohr assigned each energy level a quantum number, n.
•There are only
7 energy states.
•The 7 energy states are like rungs on a ladder, electrons
can move up or down the ladder from rung to rung, but
there is no “in between”.
•An electron can only move from one allowable orbit to
another and can only emit or absorb certain amounts of
energy.
The 1st energy level can hold only 2 e-, 2nd 8e-, 3rd 8e-, 4th
18e-, 5th 18e-, 6th 32eremember these #’s 2-8-8-18-18-32!
Ex: Draw the Bohr
model for Fluorine
# of Protons = 9
# of neutrons = 10
# of Electrons = 9
ee-e-
enucleus
e-
e-ee-
e-
Draw the Bohr Model for Ni
• # of e- =
1st level = 2e2nd level = 8e3rd level = 8e4th level = 10e-
28
e- e- eee- e- eeeeeee-e-e- nucleus e- e-eeeeeeeeeee-
Draw the Bohr model for the following elements:
Co
F
Br
Ag