Pre-IB/Pre-AP CHEMISTRY Chapter 4 Arrangement of Electrons in
Atoms
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Section 1 Objectives Be able to define: electromagnetic
radiation, electromagnetic spectrum, wavelength, amplitude,
frequency, photoelectric effect, quantum(pl. quanta), photon,
ground state, excited state, line emission spectrum, continuous
spectrum, energy level.
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Section 1 Objectives Be able to explain the mathematical
relationship between speed, wavelength, and frequency of a wave. Be
able to describe what is meant by the wave-particle duality of
light. Be able to discuss how the photoelectric effect and the line
emission spectrum of hydrogen lead to the development of the atomic
model.
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Section 1 Objectives Be able to describe the Bohr model of the
atom.
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Wave A wave is a method of transferring energy. This transfer
does not require matter as a medium.
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Wave Some waves travel through matter (sound, water waves,
etc.).
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Wave Some waves do not require matter and can travel through
empty space (light).
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Wave Properties Waves can be described by their wavelength,
amplitude, and frequency.
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Wavelength A crest is the highest point on a wave. A trough is
the lowest point on a wave. Crest Trough
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Wavelength Wavelength is simply the length of a wave. It is the
distance between two crests or two troughs. Wavelength is measured
in m, mm, or nm. Wavelength Crest Trough
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Amplitude Amplitude is simply the height of a wave. It is the
distance between the crest and trough of a wave. Amplitude is
measured in units of distance. Amplitude
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Frequency Frequency is the number of waves passing a given
point in a given time. Frequency describes the energyof a
wave.
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Frequency Frequency describes the energy of a wave: the higher
the frequency, the greater the energyof that wave.
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Frequency Frequency is measured in hertz or cycles per secondor
vibrations per second or 1/sec or sec -1 - they all mean the same
thing.
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Frequency As the wavelength increases, frequency decreases.
This is called an inverse relationship.
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Wave Properties Wavelength and amplitude give waves their
distinctive properties. For example, the loudness of a sound wave
is its amplitude, the color of visible light is its
wavelength.
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Types of waves Electromagnetic waves do not require a medium or
matter in order to travel. Light is an example.
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Light Light is an electromagnetic wave. Visible light is a
small part of the electromagnetic spectrum that humans are able to
see.
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Light The electromagnetic spectrum consists of different kinds
of light of different wavelengths.
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EM Spectrum
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Light Interactions White light is light consisting of all
colorsof visible light. These colors are visible in a rainbow or
through a prism.
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Velocity The velocity of a wave is a product of its frequency
and wavelength. v= f v = velocity f = frequency = wavelength
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Velocity The velocity of light through a vacuum(c) is about 3.0
x 10 8 m/sec. It is slightly slower through matter.
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Photoelectric Effect Photoelectric effect refers to the
emission of electrons from a metal when light shines on the
metal.
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Photoelectric Effect It was found that light of a certain
frequency would cause electrons to be emitted by a particular
metal. Light below that frequency had no effect.
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Emission Spectra If an object becomes hot enough it will begin
to emit light.
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Emission Spectra Max Planck suggested that hot objects emit
light in specific amounts called quanta (sing. quantum).
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Emission Spectra Planck showed the relationship between a
quantum of energy and the frequency of the radiation. E quantum =
hf E quantum = energy of a quantum in joules h = Plancks constant f
= frequency
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Wave-Particle Duality Einstein later said that light had a dual
nature it behaved as both a particle and a wave.
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Wave-Particle Duality Each particle of light, Einstein said,
carries a particular quantum of energy.
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Wave-Particle Duality Einstein called the particles of light
photons which had zero mass and carried a quantum of energy. The
energy is described as: E photon = hf
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Photoelectric Effect Einstein explained photoelectric effect by
saying in order for an electron to be ejected from a metal, the
photon striking it must have enough energy to eject it.
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Attraction Different metals have stronger attraction for their
electrons than other. Therefore, some must absorb more energy than
others to emit electrons.
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Ground State The lowest energy state of an atom is called its
ground state.
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Excited State When a current is passed through a gas at low
pressure, the atoms become excited.
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Excited State Atoms in an excited state have a higher potential
energy than their ground state.
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Excited State An excited atom will return to its ground state
by releasing energy in the form of electromagnetic radiation.
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Emission Spectra Elements will emit radiation of certain
frequencies. This reflects the energy states of its electrons and
is called a bright-line or emission spectrum.
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Emission Spectra The emission spectrum of an element is like
its fingerprint. SodiumHeliumMercury
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Energy Levels Studying the emission spectrum of hydrogen lead
Niels Bohr to the idea of energy levels.
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Energy Levels The spectrum Bohr and others observed was the
result of excited electrons releasing photons as they returned to
their ground states.
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Energy Levels The difference in the energy of photons was
reflected in the different frequencies of light they observed.
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Section 2 Objectives Be able to define: diffraction,
interference, Heisenberg Uncertainty Principle, Quantum Theory,
quantum numbers, principal quantum number, angular momentum quantum
number, magnetic quantum number, spin quantum number. Be able to
distinguish between the Bohr model and the quantum model of the
atom.
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Section 2 Objectives Be able to explain how the Heisenberg
Uncertainty Principle and the Schroedinger Wave Equation led to the
idea of atomic orbitals. Be able to list the four quantum numbers
that describe each electron in an atom.
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Section 2 Objectives Be able to relate the number of sublevels
corresponding to each of an atoms main energy levels, the number of
orbitals per sublevel, and the number of orbitals per main energy
level.
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Electrons as Waves French scientist Louis De Broglie
demonstrated that electrons had a dual nature also.
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Electrons as Waves De Broglie showed that electrons behaved as
waves confined to the atom. The energy of those electrons could be
found like that of waves: E = hf
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Electrons as Waves Electron beams were shown to exhibit the
wave properties of diffraction and interference.
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Heisenberg Uncertainty Werner Heisenberg tried to find the
location and velocity of electrons in the atom.
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Heisenberg Uncertainty Heisenberg found that it is impossible
to simultaneously determine the position and velocity of an
electron or any other particle (The Heisenberg Uncertainty
Principle).
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Schrdinger Wave Equation Erwin Schrdinger said that electrons
had a dual nature(like light) and treated them as waves.
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Quantum Theory Schrdingers wave equation and Heisenbergs
Uncertainty Principle laid the foundation of modern quantum
theory.
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Quantum Theory Quantum theory describes mathematically the wave
properties of electrons and other very small particles.
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Quantum Theory According to the Bohr model we should be able to
predict the location and velocity of an electron at any time.
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Quantum Theory Quantum theory disagrees with the Bohr model and
says that electrons can be found in regions of high probability but
cannot be pinpointed.
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Orbitals Quantum theory describes electrons as inhabiting a
three-dimensional region around the nucleus that indicates their
probable locations. These regions are called orbitals.
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Orbitals Scientists use quantum numbers to describe orbitals.
These numbers describe the properties of the orbitals and the
electrons which occupy them.