Download Light/Electrons

Modern Model of the Atom
The emission
of light is
fundamentally
related to the
behavior of
electrons.
Hydrogen-Atom Line-Emission Spectrum
Objective: Discuss the significance of the line-emission spectrum of hydrogen to the
development of the atomic model and how electrons exist in specific (quantized) energy levels.

Ground State
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Excited state
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The lowest energy state of an atom
State in which an atom has higher potential energy than in the ground state.
Line-Emission Spectrum
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Light is given off by excited atoms as they return to lower energy states.
Light is given off in very definite wavelengths.
Classical verses Quantum Theory
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Classical theory predicted that the hydrogen atoms would be excited
by whatever amount of energy was added and thus observe the
emission of a continuous range of frequencies of EM radiation, or a
continuous spectrum would appear.
However, lines of particular colors appeared giving a line-emission
spectrum.

Definite frequency and definite wavelength.
E2
Ephoton = E2 – E1 = hν
E1
When an excited atom with energy E2 falls back to energy E1, it releases
a photon that has a quantized amount of energy therefore a definite frequency.
The Bohr Model of the Atom
Objective: Compare and contrast the Bohr model and the quantum model of the atom.

Electron Orbits, or Energy Levels
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Electrons can only be in certain discrete orbits, and that they absorb or
emit energy in discrete amounts as they move from one orbit to another.
Each orbit thus corresponds to a definite energy level for the electron.
Pair and Share
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Distinguish between ground state and an
excited state of an atom.
Distinguish between continuous and lineemission spectrum.
Explain the meaning of quantized energy
levels in an atom and show how these levels
relate to the discrete lines in the spectrum of
that atom.
Quantum Model of the Atom
Objective: Discuss Louis de Broglie’s role in the development of the quantum model of the
atom.

Electrons as Waves
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Louis de Broglie suggested that matter in motion has
properties that are normally associated with waves.
The wave properties are especially applicable to very small
particles, such as electrons.
Each particle’s wavelength is related to its mass, its velocity
and Planck’s constant.
Smaller the mass, and greater the velocity, the more
wavelike the characteristics.
h

mv
Heisenberg Uncertainty Principle
Objective: Explain the significance of the Heisenberg Uncertainty Principle on the
development of the modern atomic model.

States that it is impossible to determine
simultaneously both the position and velocity
of an electron.


Electrons are detected by their interaction with
photons.
Because photons have about the same energy as
electrons, any attempt to locate a specific electron
with a photon knocks the electron off its course.
Schrödinger Wave Equation
Objective: Discuss the impact of the Schrödinger Wave Equation on the development of the
modern atomic model and the location of electrons around the atom.


Predicts a three dimensional region around the nucleus
called an atomic orbital that describes the electron’s
probable location.
The boundary of the atomic orbital is defined as the
volume that encloses a 90% probability of containing its
electrons.
Atomic Orbitals
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An atomic orbital is a region of space in which the
probability of finding an electron is high.
Electrons have a designated arrangement in all
atoms. The atomic orbitals have specific energy
levels and shapes in which the electrons are
distributed.
These are referred to as the following:
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Principal energy levels
Energy Sublevels
Orbitals
Number of electrons in an orbital (electron spin).
Principal Energy Level
Objective: Identify the principle energy levels in an atom and state the energy trend among them.
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The principal energy level , symbolized by n, indicates
the main energy level occupied by the electron.
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Values of n are positive integers only: n = 1,2,3,…..
Increases in energy and size as one moves away from nucleus.
Also related to the periods of the periodic table.
The number of orbitals possible per energy level is equal to n2
n=5
n=4
n=3
E
n
e
r
g
y
n=2
n=1
Energy Sublevels
Objective: For each principle energy level, state the number of sublevels, identify them, and
state the energy trend among them.


Indicates the shape of the orbital
Number of orbital shapes allowed in an energy level equals n.

Shapes of the first four orbitals are designated s, p, d, f
Electron Orbitals
Objective: Sketch the general shapes of the s and p orbitals. State the number of orbitals in
each sublevel and the distribution of electrons in s, p, d, and f sublevels.

Each sublevel has a different number of orbitals.

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s – one possible orbital in space
p – three possible orbitals in space
d – five possible orbitals in space
f – seven possible orbitals in space
Electron Spin

A single orbital can contain only two electrons,
which must have opposite spins.
Shapes of Orbitals
Shapes Cont.
Modern Atom Model Chart Organizer
Objective: Relate the number of sublevels corresponding to each of an atom’s main energy
levels, the number of orbitals per sublevel, the number of electrons per sublevel and main
energy level.
Principal
Energy Level
(n)
Sublevels in
main energy
level
(n sublevels)
Number of
orbitals per
sublevel
Number of
electrons
per sublevel
Number of electrons
per principal energy
level (2n2)
1
s
1
2
2
2
s
p
1
3
2
6
8
3
s
p
d
1
3
5
2
6
10
18
4
s
p
d
f
1
3
5
7
2
6
10
14
32