Chapter 7 Guided Notes
A _______________________________________ is a continuously repeating change or oscillation in
matter or in a physical field.
Light is an ______________________________________________________, consisting of oscillations in
electric and magnetic fields traveling through space.
A wave can be characterized by its _________________________________and
_________________________________________________.
___________________________, symbolized by the Greek letter lambda, l, is the distance between any
two identical points on adjacent waves.
_________________________________________________ symbolized by the Greek letter nu, n, is the
number of wavelengths that pass a fixed point in one unit of time (usually a second). The unit is 1/S or s-1,
which is also called the __________________________ (Hz).
Wavelength and frequency are related by the wave speed, which for light is c, the speed of light,
________________________________________
Formula:
The relationship between wavelength and frequency due to the constant velocity of light is illustrated
on the next slide.
When the wavelength is reduced by a factor of two, the frequency increases by a factor of
__________________________.
What is the wavelength of blue light with a frequency of 6.4 × 1014/s?
What is the frequency of light having a wavelength of 681 nm?
The range of frequencies and wavelengths of electromagnetic radiation is called the electromagnetic
spectrum.
One property of waves is that they can be ________________________________________—that is,
they spread out when they encounter an obstacle about the size of the wavelength.
In 1801, Thomas Young, a British physicist, showed that light could be diffracted. By the early 1900s, the
wave theory of light was well established.
The wave theory could not explain the __________________________________________, however.
The ______________________________________________________________is the ejection of an
electron from the surface of a metal or other material when light shines on it.
Einstein proposed that light consists of quanta or particles of electromagnetic energy, called
________________________________. The energy of each photon is proportional to its
__________________________________________:
E = hn
h = 6.626 × 10-34 J  s (Planck’s constant)
Einstein used this understanding of light to explain the photoelectric effect in 1905.
Each electron is struck by a single photon. Only when that photon has enough energy will the electron
be ejected from the atom; that photon is said to be absorbed.
Light, therefore, has properties of both waves and matter. Neither understanding is sufficient alone. This
is called the ____________________________________________________________________
The blue–green line of the hydrogen atom spectrum has a wavelength of 486 nm. What is the energy of
a photon of this light?
In addition, this understanding could not explain the observation of line spectra of atoms.
A ______________________________________________________________ contains all wavelengths
of light.
A ______________________________________________________________ shows only certain colors
or specific wavelengths of light. When atoms are heated, they emit light. This process produces a line
spectrum that is specific to that atom. The emission spectra of six elements are shown on the next slide.
In 1913, Neils Bohr, a Danish scientist, set down postulates to account for
1. The stability of the hydrogen atom
2. The line spectrum of the atom
Energy-Level Postulate
An electron can have only certain energy values, called energy levels. Energy levels are quantized.
For an electron in a hydrogen atom, the energy is given by the following equation:
RH = 2.179 x 10-18 J
n = principal quantum number
Transitions Between Energy Levels
An electron can change energy levels by absorbing energy to move to a higher energy level or by
___________________ energy to move to a lower energy level.
For a hydrogen electron the energy change is given by:
The energy of the emitted or absorbed photon is related to DE:
Light is absorbed by an atom when the electron transition is from lower n to higher n (nf > ni). In this
case, DE will be ___________________________________.
Light is emitted from an atom when the electron transition is from higher n to lower n (nf < ni). In this
case, DE will be ____________________________
An electron is ejected when : ___________________________
Problem: What is the wavelength of the light emitted when the electron in a hydrogen atom undergoes
a transition from n = 6 to n = 3?
Planck
Vibrating atoms have only certain energies:
E = hn or 2hn or 3hn
Einstein
Energy is quantized in particles called photons:
E = hn
Bohr
Electrons in atoms can have only certain values of
energy. For hydrogen:
E
RH
n2
RH  2.179 x 10 18 J, n  principal quantum number
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Light has properties of both waves and particles (matter).
What about matter?
In 1923, Louis de Broglie, a French physicist, reasoned that particles (matter) might also have wave
properties.
The wavelength of a particle of mass, m (kg), and velocity, v (m/s), is given by the de Broglie relation:
Compare the wavelengths of
(a) an electron traveling at a speed that is one-hundredth the speed of light and (b) a baseball of mass
0.145 kg having a speed of 26.8 m/s (60 mph).
Building on de Broglie’s work, in 1926, Erwin Schrödinger devised a theory that could be used to explain
the wave properties of electrons in atoms and molecules.
The branch of physics that mathematically describes the wave properties of submicroscopic particles is
called _______________________________________________________________________________.
Quantum mechanics alters how we think about the motion of particles.
In 1927,__________________________________________________ showed how it is impossible to
know with absolute precision both the position, x, and the momentum, p, of a particle such as electron.
Because p = mv this uncertainty becomes more significant as the mass of the particle becomes smaller.
Quantum mechanics allows us to make statistical statements about the regions in which we are most
likely to find the ____________________________________.
Solving Schrödinger’s equation gives us a wave function, represented by the Greek letter psi, y, which
gives information about a particle in a given energy level.
Psi-squared, y 2, gives us the probability of finding the particle within a region of space.
Two additional views are shown on the next slide.
Figure A illustrates the probability density for an electron in hydrogen. The concentric circles represent
successive shells.
Figure B shows the probability of finding the electron at various distances from the nucleus. The highest
probability (most likely) distance is at 50 pm.
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According to quantum mechanics, each electron is described by four quantum numbers:
1.
2.
3.
4.
The first three define the _______________________________________for a particular electron. The
fourth quantum number refers to the ________________________________________ of electrons.
A wave function for an electron in an atom is called an atomic orbital (described by three quantum
numbers—n, l, ml). It describes a region of space with a definite shape where there is a high probability
of finding the electron.
We will study the quantum numbers first, and then look at atomic orbitals.
Principal Quantum Number, n
Angular Momentum Quantum Number, l
Magnetic Quantum Number, ml
Summary:
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The figure
shows
relative
energies for
the hydrogen
atom shells
and
subshells;
each orbital
is indicated
by a dashedline.
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Spin Quantum Number, ms
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Which of the following are permissible sets of quantum numbers?
n = 4, l = 4, ml = 0, ms = ½
n = 3, l = 2, ml = 1, ms = -½
n = 2, l = 0, ml = 0, ms = ³/²
n = 5, l = 3, ml = -3, ms = ½
Atomic Orbital Shapes
S
P
D
The cross-sectional view
of a 1s orbital and a
2s orbital highlights the
difference in the two
orbitals’ sizes.
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The complexity of the d orbitals can be seen below
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