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Lecture Presentation
Chapter 4
Subatomic
Particles
Bradley Sieve
Northern Kentucky University
Highland Heights, KY
© 2014 Pearson Education, Inc.
4.1 Physical and Conceptual Models
• Atoms are so small we cannot “see” them
• Atoms are smaller than wavelengths of
visible light
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4.1 Physical and Conceptual Models
• Atoms are imaged indirectly
– Scanning probe microscope
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4.1 Physical and Conceptual Models
• Physical model
– A model of something very large or very small
– Replicates an object in a convenient scale
• Conceptual model
– Helps predict how a system behaves
– The more accurate the model, the more
accurately it makes predictions
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Concept Check
A basketball coach describes a playing strategy to
her team by way of sketches on a game card. Do
the illustrations represent a physical model or a
conceptual model?
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Concept Check
The sketches are a conceptual model the coach
uses to describe a system (the players on the
court), with the hope of achieving an outcome
(winning the game).
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4.1 Physical and Conceptual Models
• Conceptual model of an atom
– Contains three main parts
• Electron, proton, and neutron
• Planetary model of the atom
– Limited in ability to make predictions
– Has been updated to include shells
• While limited, such models are excellent
guides
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4.2 The Electron Was the First Subatomic
Particle Discovered
• Scientists realized that electricity could
pass through glass tubes as glowing rays
– Both with and without a gas in the tube
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4.2 The Electron Was the First Subatomic
Particle Discovered
• The rays exhibited a negative charge
– Became known as cathode rays
– Appeared to behave as a beam of particles
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4.2 The Electron Was the First Subatomic
Particle Discovered
J. J. Thomson
– Reasoned that the amount of deflection
related to mass and charge
• The greater the mass the less the deflection
• The larger the charge the more the deflection
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4.2 The Electron Was the First Subatomic
Particle Discovered
Robert Millikan
– Conducted the oil drop experiment
– Was able to calculate the electric charge of a
cathode particle
• Found value to be 1.60 x 10-19 coulomb
– Derived the cathode ray particle’s mass
• Found to be 9.1 x 10-31
• Much less than the hydrogen atom’s mass
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4.2 The Electron Was the First Subatomic
Particle Discovered
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4.2 The Electron Was the First Subatomic
Particle Discovered
J. J. Thomson
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Robert Millikan
4.2 The Electron Was the First Subatomic
Particle Discovered
• Electron
– The particle found in cathode rays
– A fundamental unit of all atoms
– Exhibits a negative charge
– Possesses a very small mass (9.1 x 10-31 kg)
– Determine many physical and chemical
properties of atoms
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4.3 The Mass of an Atom Is Concentrated
in Its Nucleus
• Plum-pudding model
– Common model for the atom
– Has negative and positive particles intermixed
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4.3 The Mass of an Atom Is Concentrated
in Its Nucleus
Ernest Rutherford
– Oversaw the gold-foil experiment
• Passed alpha particles through a thin gold foil
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4.3 The Mass of an Atom Is Concentrated
in Its Nucleus
• Most particles passed
right through the foil
• Some alpha particles
were deflected
– Deflected particles
must have interacted
with a dense positively
charged center
• Named these centers
the atomic nucleus
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4.3 The Mass of an Atom Is Concentrated
in Its Nucleus
• Atomic Model
– Nucleus is drawn at the center of atom
– Electrons fill space around nucleus
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
• Protons
– Positively charged particles in the nucleus
– Nearly 2000 times as massive as the electron
– Number of protons is equal to number of
electrons if charges are balanced
• Atomic number
– The number of protons an element contains
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Concept Check
How many protons are in an iron atom, Fe (atomic
number 26)?
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Concept Check
The atomic number of an atom and its number of
protons are the same. Thus, there are 26 protons
in an iron atom. Another way to put this is that all
atoms that contain 26 protons are, by definition,
iron atoms.
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
• Neutron
– Discovered by James Chadwick in 1932
– Roughly the same mass as a proton
– Exhibits no electric charge
– Contributes mass to the atom along with
the proton
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
• Nucleons
– Particles located in the nucleus
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
Subatomic Particles
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
• Isotopes
– Atoms with the same number of protons but
different numbers of neutrons
– Exhibit different mass numbers
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
• Isotope Symbol
– Shows element, atomic number, and mass
– Number of neutrons can be found by
subtracting atomic number from mass
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4.4 The Atomic Nucleus Is Made of Protons
and Neutrons
• Atomic Mass
– Total mass of an atom
– Electron mass is negligible
– Uses a special unit called the atomic mass
unit (amu)
• 1 amu is equal to 1.661 x 10-24 grams
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4.5 Light Is a Form of Energy
• Electromagnetic waves
– Oscillations of electric and magnetic fields
– Wavelength
• The distance between two crests of a wave
– Wave frequency
• Measure of how rapidly waves oscillate
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4.5 Light Is a Form of Energy
• Electromagnetic spectrum
– Full range of frequencies and wavelengths
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Concept Check
Can you see radio waves? Can you hear them?
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Concept Check
Radio waves are one type of electromagnetic
radiation, but their frequency is much lower than
what your eyes can detect. Nor can you hear
them. A radio translates radio waves into signals
that drive a speaker to produce sound waves your
ears can hear.
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4.5 Light Is a Form of Energy
• Spectroscope
– An instrument used to observe colors
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4.6 Atomic Spectra and the Quantum
Hypothesis
• Atoms only emit
certain frequencies
based on the type
– Each atom type
emits a discrete and
distinct pattern
– This pattern is called
the atomic spectrum
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Concept Check
How might you deduce the elemental composition
of a star?
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Concept Check
Aim a well-built spectroscope at the star, and study
its spectral patterns. Each element contained in
the star will have its atomic spectrum present.
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4.6 Atomic Spectra and the Quantum
Hypothesis
Max Planck
– Hypothesized that light
energy is quantized
– The total amount of
energy must be equal to a
multiple of a fundamental
unit of energy
– Identified each discrete
parcel as a quantum
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4.6 Atomic Spectra and the Quantum
Hypothesis
Niels Bohr
– Explained the atomic spectra using Planck’s
quantum hypothesis
1. An electron has more potential energy when
farther from the nucleus
2. When an atom absorbs a photon of light, it is
absorbing energy
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4.6 Atomic Spectra and the Quantum
Hypothesis
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4.6 Atomic Spectra and the Quantum
Hypothesis
• Energy of an electron is quantized
– It cannot have just any value of energy
– Each step is one quantum level
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4.6 Atomic Spectra and the Quantum
Hypothesis
• Bohr’s planetary model
–Electrons orbit the nucleus at certain intervals,
similar to planets orbiting the sun
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4.6 Atomic Spectra and the Quantum
Hypothesis
• Bohr’s explanation of why only certain light
frequencies are seen
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4.7 Electrons Exhibit Wave Properties
• Wave-Particle Duality
– Idea that matter can behave as a wave or as
a particle
• Electron wave behavior explains why
electrons are restricted to particular
energy levels
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Concept Check
What must an electron be doing to have wave
properties?
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Concept Check
According to de Broglie, particles of matter behave
like waves by virtue of their motion, which is a form
of energy. An electron must therefore be moving to
have wave properties.
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4.8 The Noble Gas Shell Model Simplifies
the Energy-Level Diagram
• Energy level diagrams
– Shows orbitals of similar energy together
– Contains seven rows of grouped orbitals
• Corresponding to the seven periods of the periodic
table
– The higher the energy, the further the
grouping from the nucleus
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• Pairing of electrons occurs only after the
shell is half full
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Concept Check
Why are there only two elements in the first period
of the periodic table?
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Concept Check
The number of elements in each period
corresponds to the number of electrons each shell
can hold. The first shell has a capacity of only two
electrons, which is why the first period has only
two elements.
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
• Periodic Trend
– Gradual change of a property across the
periodic table
– Largely due to two concepts
• Inner-shell shielding
• Effective nuclear charge
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
• Inner-shell shielding
– Inner shell electrons reduce the attraction of
the nucleus on outer shell electrons
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
• Effective nuclear charge
– The reduced attraction the outer shell
electrons experience
– Abbreviated as Z*
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
• Calculating Z*
– Z* is roughly the nuclear charge minus the
inner-shell electrons
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
• Atomic diameter trends
– Atoms in the upper right of the periodic table
are smaller
– This is due to two behaviors
• The further left an element is, the higher the
effective nuclear charge the outer electrons feel
• Atoms higher on the periodic table have fewer
occupied shells
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
• Smallest atoms have the most strongly
held electrons
– Exhibit higher Z* values on the outermost
electrons
– Have fewer inner shells, so the outer
electrons are closer to the nucleus
– Described by the ionization energy needed to
free an electron
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
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4.9 The Periodic Table Helps Us Predict
Properties of Elements
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Concept Check
Which loses one of its outermost electrons more
easily: a francium, Fr, atom (atomic number 87) or
a helium, He, atom (atomic number 2)?
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Concept Check
A francium, Fr, atom loses electrons more easily
than does a helium, He, atom. Why? Because a
francium atom’s outer electrons are not held as
tightly by its nucleus, which is buried deep beneath
many layers of shielding electrons.
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