Transcript Section 5-1
Section 5.1 Light and Quantized Energy
•
Compare
the wave and particle natures of light.
•
Define
a quantum of energy, and explain how it is related to an energy change of matter.
•
Contrast
continuous electromagnetic spectra and atomic emission spectra.
radiation:
the rays and particles —alpha particles, beta particles, and gamma rays —that are emitted by radioactive material Section 5-1
Section 5.1 Light and Quantized Energy (cont.)
electromagnetic radiation wavelength frequency amplitude electromagnetic spectrum quantum Planck's constant photoelectric effect photon atomic emission spectrum
Light, a form of electronic radiation, has characteristics of both a wave and a particle.
Section 5-1
The Atom and Unanswered Questions
• Recall that in Rutherford's model, the atom’s mass is concentrated in the nucleus and electrons move around it.
• The model doesn’t explain how the electrons were arranged around the nucleus.
• The model doesn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus.
• It doesn’t explain why some elements are similar…or why some are different.
Section 5-1
The Atom and Unanswered Questions (cont.)
• In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame.
• Analysis of the emitted light revealed that an element’s
atoms.
chemical behavior is related to the arrangement of the electrons in its
Section 5-1
The Wave Nature of Light
• Visible light is a type of
electromagnetic radiation
space.
, a form of energy that exhibits wave-like behavior as it travels through • There are many types of electromagnetic radiation: Xray, Gamma rays, UV, radio, microwave, infrared and visible. • All waves can be described by several characteristics.
Section 5-1
The Wave Nature of Light (cont.)
• The
wavelength
(λ) is the shortest distance between equivalent points on a continuous wave.
• The
frequency
(f) is the number of waves that pass a given point per second.
known as a Hertz.
The unit for frequency is 1/sec or sec-1, which is
• The
amplitude
origin to a crest.
is the wave’s height from the Section 5-1
The Wave Nature of Light (cont.)
All electromagnetic waves travel at 3.00 x 10 8 vacuum.
m/s in a Section 5-1
The Wave Nature of Light (cont.)
• The speed of light (3.00 product of it’s wavelength and frequency
c
= λf.
10 8 m/s) is the
c =
f
Section 5-1
• EX: Find the frequency of a photon with a
wavelength of 434 nm.
GIVEN: WORK : f = ?
= 434 nm = 4.34
c = 3.00
10
-7
m 10
8
m/s f = c
f = 3.00
4.34
10
8
10 m/s
-7
m f
= 6.91
10
14
Hz
EM Spectrum
The Wave Nature of Light (cont.)
• Sunlight contains a continuous range of wavelengths and frequencies.
• A prism separates sunlight into a continuous spectrum of colors.
• The
electromagnetic spectrum
includes all forms of electromagnetic radiation.
Section 5-1
The Wave Nature of Light (cont.)
Wavelength and frequency are inversely related. If one increases,
the other decreases . Energy is directly related to frequency.
Section 5-1
The Particle Nature of Light
• The wave model of light cannot explain all of light’s characteristics.
• Matter can gain or lose energy only in small, specific amounts called quanta.
•
Max Planck
(1900) observed - emission of light from hot objects •
Concluded
- energy is emitted in small, specific amounts (quanta) • A
quantum
is the minimum amount of energy that can be gained or lost by an atom.
•
Planck’s constant
6.626 10 –34 J ● has a value of
s. J = Joule, the unit for Energy.
Section 5-1
The Particle Nature of Light (cont.)
• The
photoelectric effect
is when electrons are emitted from a metal’s surface when light of a certain frequency shines on it.
Section 5-1
The Particle Nature of Light (cont.)
• Albert Einstein proposed in 1905 that light has a dual nature.
• A beam of light has wavelike and particle like properties.
• A
photon
is a particle of electromagnetic radiation with no mass that carries a quantum of energy.
=
hf E
photon
E = h
f
E
photon
h
represents energy.
is Planck's constant.
f
represents frequency. Section 5-1
• EX: Find the energy of a red photon with a frequency of 4.57
10
14
Hz.
GIVEN: E = ?
f = 4.57
10 h = 6.6262
14
Hz 10
-34
J·s WORK E = hf : E =
( 6.6262 10 -34 J·s )( 4.57 10 14 Hz )
E = 3.03
10
-19
J
Quantum Theory
Atomic Emission Spectra
• Light in a neon sign is produced when electricity is passed through a tube filled with neon gas and excites the neon atoms.
• The excited atoms emit light to release energy.
Section 5-1
Atomic Emission Spectra (cont.)
Section 5-1
Atomic Emission Spectra (cont.)
• The
atomic emission spectrum
of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element.
• Each element’s atomic emission spectrum is unique. Like a finger print.
Section 5-1
Section 5.1 Assessment What is the smallest amount of energy that can be gained or lost by an atom? A.
electromagnetic photon
B.
beta particle
C.
quanta
D.
wave-particle
A 0%
A. A B. B
B 0%
C. C
0%
D. D
C 0% D
Section 5-1
Section 5.1 Assessment What is a particle of electromagnetic radiation with no mass called?
A.
beta particle
B.
alpha particle
C.
quanta
D.
photon
A 0%
A. A B. B
B 0%
C. C
0%
D. D
C 0% D
Section 5-1