Download Ch. 4: Electron Configuration

Arrangement of Electrons in
Atoms
• Principles of electromagnetic radiation led
to Bohr’s model of the atom.
• Electron location is described using
identification numbers called quantum
numbers.
• Rules for expressing electron location
results in a unique electron configuration
for each element.
Mullis Chemistry Holt Ch.4
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Building electron configurations for the ground state of an atom
Aufbau: Lowest energy level 1st
Pauli Exclusion: Only 2 e- per orbital, opposite spin
Hund: One electron per orbital until that level is full (same spin)
Theater analogy:
1. Enter at front. Climb stairs and sit in first empty section you reach.
2. Each bench seats 2 people. One male and one female per bench.
3. Within a level, ladies first. One lady per bench until each bench
is occupied, then one man per bench to fill that level.
Mullis Chemistry Holt Ch.4
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Example: Building electron configurations for the ground state of an atom
Phosphorous: 15 electrons:
Start with 1s. Each s can hold 2 electrons. Each p can hold 6 electrons.
Place one electron per orbital, then pair until that level is full. Only then go to the next level.
Mullis Chemistry Holt Ch.4
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Wave Description of Light
• Electromagnetic radiation is a form of energy that
exhibits wavelike behavior as it travels through space
• Wavelength (λ)
– Distance between corresponding points on adjacent waves.
– Unit: nm,cm,m
• Frequency (ν)
– Number of waves that pass a specific point in a given time
– Unit: Hz or waves/sec
Recall that Speed = Distance/time (m/sec)
• Speed of light (c)
C=λν
Mullis Chemistry Holt Ch.4
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Behavior of Light
• Photoelectric effect
– The emission of electrons when light shines on
the metal
– Scientists found that below a certain frequency,
no electrons were emitted.
– Light also behaves as a particle: Since hot
objects do not emit em energy continuously,
they must emit energy in small chunks called
quanta.
• Quantum
– Minimum quantity of energy that can be gained
or lost by an atom
Mullis Chemistry Holt Ch.4
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Light as a particle and a wave
Planck and Einstein
• Max Planck: Relationship between quantum of
energy and wave frequency
• Planck’s constant h = 6.626 x 10-34 J-s
E = hν
E is energy, ν is frequency
• Albert Einstein: Established dual wave-particle
nature of light 1st
– Einstein explained PE effect by proposing that EM
radiation is absorbed by matter only in whole numbers
of photons.
– Electron is knocked off metal surface only if struck by
one photon with certain minimum energy.
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Quantum Theory
• Ground state: An atom’s lowest energy state
• Excited state: Higher potential energy than ground
state.
• Photon: A particle of electromagnetic radiation
having zero mass and carrying a quantum of energy
(i.e., packet of light)
• Only certain wavelengths of light are emitted by
hydrogen atoms when electric current is passed
through—Why?
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Niels Bohr links hydrogen’s
electron with photon emission
• Bohr proposed that an electron circles the
nucleus in allowed orbits at specific energy
levels.
– Lowest energy is close to nucleus
• Bohr’s theory explained the spectral lines
seen in hydrogen’s line emission spectrum,
but it did not hold true for other elements.
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Quantum Numbers
•
•
•
•
Principal quantum number
Angular momentum quantum number
Magnetic quantum number
Spin quantum number
Mullis Chemistry Holt Ch.4
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Quantum numbers
1s ____
2s ____
3s _____
Principal quantum number
2p ____ ____ ____
Magnetic quantum number
Angular momentum quantum number
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Magnetic quantum number
• Magnetic quantum number is the orientation of an
orbital around the nucleus.
• It is the number of orbitals in a sublevel.
Orbitals per sublevel
The s sublevel has 1 orbital.
The p sublevel has 3 orbitals.
The d sublevel has 5 orbitals.
The f sublevel has 7 orbitals.
Mullis Chemistry Holt Ch.4
s
p
d
f
1
3
5
7
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Atomic Structure
Summary of Contributions
• Max Planck
– A hot object emits energy in small, specific amounts
called quanta.
• Albert Einstein
– E = mc2
– Light behaves as both a wave and a particle.
– Each particle of light carries a photon ( a quantum of
energy).
• Niels Bohr
– Created a model of the atom that showed a single
electron of hydrogen orbits the nucleus only in
Mullis Chemistry Holt Ch.4
allowed orbits with a fixed energy.
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Atomic Structure
Summary of Contributions,
continued
• Werner Heisenberg
– Uncertainty principle: It is impossible to
determine simultaneously both the position and
velocity of an electron.
• Erwin Schrödinger
– Helped lay the foundation for quantum theory
with an equation that treats electrons like
waves.
Mullis Chemistry Holt Ch.4
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Electron Configuration: The Rules
• Aufbau principle
– An electron occupies the lowest energy orbital that will
receive it.
• Pauli exclusion principle
– No two electrons in the same atom can have the same set
of 4 quantum numbers.
– Therefore, electrons can pair in an orbital as long as their
spins are opposite.
• Hund’s rule
– Each of the orbitals at a particular level have one electron
before any of them can have two electrons.
– All single electrons in the orbitals at a particular level
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have the same spin.Mullis Chemistry Holt Ch.4