Notes # _____
Chemistry Chapter 5 Notes, Part IV
Date: _______
5.3 Light
Waves are disturbances that transmit _______________ either through a substance, called a
________________, or through empty space ( a ________________). __________________________
waves are produced by disturbances in electric and magnetic fields (hence, EM).
____________________ often cause waves. Light is EM radiation that travels as a transverse
wave but is _______________ (given off) or _______________ (taken in) as a massless particle
called a _____________. This is called the “wave-particle duality” of light. James Maxwell
proposed the Electromagnetic theory that states an electromagnetic wave, such as light, is
a periodic disturbance involving electric and magnetic fields. The speed of light is affected
by its medium, decreasing when the medium gets ______________. Since light travels as an
EM wave it does not require a medium so it travels ____________ in a vacuum. The speed of
light, represented as ____, is equal to _____________ m/s ( ______________________m/s) or
about _______________ miles per second!! At this speed light would travel _____ times
around the Earth in one second; from the moon to the Earth in _____ seconds; and from
the Sun to Earth (93 million miles) in ______________________.
Wave Characteristics
The _____________ (
) is the time required for one full wave to pass a point--it is
measured in _____________. The _________________ (
is the reciprocal of the ______________ ( so
) is how often a wave passes by--it
= –—– ). So, if the period is 10.0 seconds
the frequency is ________ or __________. [ or ________ which is also _____________ (
Example 1:
_____________________________________________
since T = ______ f = ________ = _________
)]
Figure 5-10 (on p. 139) shows the range of visible light and the entire EM spectrum. Note:
_______ frequencies = _________ wavelengths and the ___________ the frequency the
___________ the energy. Visible light has wavelengths between ______ nm (
_______ nm (
).
Note 1 ________________ (
) = _______ m or _______ nm.
) and
Speed of Light
Recall that velocity equals distance ÷ time so:
Example 2:
What is the velocity of a 1.0 m wave if its period is 4.0 seconds?
Example 3:
What is the wavelength if a wave traveling at 15.0 m/s has a frequency of 5 Hz?
Production of Light
When an atom gains a specific energy, called a ______________, electrons in its electron
cloud will jump to higher energy levels (further from the nucleus) then immediately “fall”
back down to lower levels. Regardless of how the energy was originally gained by the
electron (heat, electricity, sound), the released energy is always light. Depending on the
amount of energy released different colors can be produced following the pattern:
ROY G BIV.
The pattern of light produced is called the _____________ _____________ _______________ of
the element and might look like this for the element to the left:
Each element has its own unique fingerprint that
can be used to identify it. When all of the
electrons of an atom are in their lowest energy
the atom is said to be in its _______________ state.
If a quantum of energy is applied to the atom an
electron (or more) can jump to higher energy
levels and the atom is in an __________________
state.
When the electron falls back to the ground state the energy released can be found using
the equation:
Where E is the energy in J
h, is the Planck’s constant (6.626 x 10
–34
J·s)
–1
f is the frequency in hertz (s )
or, if one knows the wavelength the following equation can be used:
Where c is the speed of light
λ is the wavelength in meters
The atomic emission spectrum for hydrogen had been intensely studied. Since there is
only one electron in its spectrum we can look closely at its pattern. In the diagram below
one ground state and two excited states are shown. Each of the series has a name and a
corresponding energy in the EM spectrum: