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Electrons in the Atom
Chapter 5
Section 5.1 Light and Quantized Energy
•
1. The
Nuclear 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.
• 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 chemical behavior is related to the
arrangement of the electrons in its atoms.
2. The Wave
Nature of Light
• Visible light is a type of electromagnetic
radiation, a form of energy that exhibits
wave-like behavior as it travels through
space.
• All waves can be described by several
characteristics.
• The wavelength (λ) is the shortest distance
between equivalent points on a continuous
wave.
• The amplitude is the wave’s height from the
origin to a crest.
The Wave Nature
of Light (cont.)
• The frequency (ν) is the number of waves
that pass a given point per second.
• One hertz (Hz), the SI unit of frequency, equals
one wave per second
• The speed of light (3.00  108 m/s) is the
product of it’s wavelength and frequency
c = λν.
• Although the speed of all electromagnetic
waves is the same, waves may have
different wavelengths and frequencies.
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.
• Continuous means there is no portion
of it that does not correspond to a
unique wavelength and frequency of
light
• The electromagnetic spectrum
(EM) includes all forms of
electromagnetic radiation.
• Energy increases with increasing
frequency.
3. 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.
• A quantum is the minimum amount of
energy that can be gained or lost by an
atom.
Equantum = h
• Planck’s constant has a value of
6.626  10–34 J ● s.
• The Joule (J) is the SI unit of energy
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.
• Albert Einstein proposed in 1905 that light
has a dual nature.
• A beam of light has wavelike and
particlelike properties.
• A photon is a particle of electromagnetic
radiation with no mass that carries a
quantum of energy.
Ephoton = h
Ephoton represents energy.
h is Planck's constant.
 represents frequency.
4. 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.
• 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.
End of Section 5.1
Section 5.2 Quantum Mechanics and the Atom
5. Bohr's Model
of the Atom
• Bohr correctly predicted the frequency lines
in hydrogen’s atomic emission spectrum.
The lowest allowable energy state of an
atom is called its ground state.
• When an atom gains energy, it is in an
excited state.
• Bohr suggested that an electron moves
around the nucleus only in certain allowed
circular orbits.
• Each orbit was given a number, called the
quantum number.
Bohr's Model of
the Atom (cont.)
• Hydrogen’s single electron
is in the n = 1 orbit in the
ground state.
• When energy is added, the
electron moves to the n = 2
orbit.
• Bohr’s model explained the
hydrogen’s spectral lines,
but failed to explain any
other element’s lines.
• The behavior of electrons
is still not fully understood,
but it is known they do not
move around the nucleus
in circular orbits.
6. The Quantum
Mechanical Model
of the Atom
• Louis de Broglie (1892–1987)
hypothesized that particles, including
electrons, could also have wavelike
behaviors.
• The figure illustrates that electrons orbit the
nucleus only in whole-number
wavelengths.
• The de Broglie equation predicts that all
moving particles have wave characteristics.
The Quantum
Mechanical Model
of the Atom (cont.)
• Heisenberg showed it is impossible to
take any measurement of an object
without disturbing it.
• The Heisenberg uncertainty
principle states that it is
fundamentally impossible to know
precisely both the velocity and position
of a particle at the same time.
• The only quantity that can be known is
the probability for an electron to
occupy a certain region around the
nucleus.
The Quantum
Mechanical Model
of the Atom (cont.)
• Schrödinger treated electrons as waves in
a model called the quantum mechanical
model of the atom.
• Schrödinger’s equation applied equally well
to elements other than hydrogen.
• The wave function predicts a threedimensional region around the nucleus
called the atomic orbital.
• Principal quantum number (n) indicates
the relative size and energy of atomic
orbitals.
7. Hydrogen
Atomic Orbitals
• n specifies the atom’s major energy levels,
called the principal energy levels.
• Energy sublevels are contained within the
principal energy levels.
• Each energy sublevel relates to orbitals of
different shape.
End of Section 5.2
Section 5-3 Electron Configuration
8. Ground-State
Electron
Configuration
• The arrangement of electrons in the atom is
called the electron configuration.
• The aufbau principle states that each electron
occupies the lowest energy orbital available.
Ground-State
Electron
Configuration (cont.)
• The Pauli exclusion
principle states that a
maximum of two
electrons can occupy a
single orbital, but only if
the electrons have
opposite spins.
• Hund’s rule states that
single electrons with the
same spin must occupy
each equal-energy orbital
before additional
electrons with opposite
spins can occupy the
same energy level
orbitals.
Ground-State
Electron
Configuration (cont.)
• Noble gas notation uses noble gas
symbols in brackets to shorten inner
electron configurations of other elements.
• The electron configurations (for chromium,
copper, and several other elements) reflect
the increased stability of half-filled and
filled sets of s and d orbitals.
9. Valence
Electrons
• Valence electrons are defined as
electrons in the atom’s outermost orbitals—
those associated with the atom’s highest
principal energy level.
• Electron-dot structure consists of the
element’s symbol representing the nucleus,
surrounded by dots representing the
element’s valence electrons.
End of Section 5.3
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CIM
Figure 5.11 Balmer Series
Figure 5.12 Electron Transitions
Table 5.4
Electron Configurations and Orbital
Diagrams for Elements 1–10
Table 5.6
Electron Configurations and
Dot Structures
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