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Electrons in Atoms
These slides are adapted from Mr. Ammann’s Chapter 13 PowerPoint at Milbank High School.
Models of the Atom ● OBJECTIVES:
- Summarize the development of atomic theory.
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Models of the Atom ● OBJECTIVES:
- Explain the significance of quantized energies of electrons as they relate to the quantum mechanical model of the atom.
J. J. Thomson’s Model ● Discovered electrons ● Negative electron
floating around ● “Plum-Pudding”
model
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Ernest Rutherford’s Model ● Discovered dense
positive piece at the center of the atom- nucleus
● “Nuclear model”
Niels Bohr’s Model ● Move like planets around the sun. ● In circular orbits at different levels. ● Amounts of energy separate one
level from another. ● “Planetary model”
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Bohr’s planetary model ● electron cannot exist between energy
levels, just like you can’t stand between rungs on ladder
● Quantum of energy required to move to the next highest level
● Has energy levels for electrons.
● Orbits are not circular. ● It can only tell us the
probability of finding an electron a certain distance from the nucleus.
The Quantum Mechanical Model
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● The atom is found inside a blurry “electron cloud”
● An area where there is a chance of finding an electron.
● Think of fan blades
The Quantum Mechanical Model
Atomic Orbitals
● Atomic orbital - areas where there is a high probability of finding an electron.
● (n) = the energy level of the electron. ● Energy level shells have several
shapes. ● Subshells
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Summary
s
p
d
f
Max electrons
Starts at energy level
2 1
6 2
10 3
14 4
Orbital
By Energy Level First Energy Level ● only s orbital ● only 2 electrons ● 1s2
Second Energy Level
● s and p orbitals are available
● 2 in s, 6 in p ● 2s22p6
● 8 total electrons
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By Energy Level Third energy level ● s, p, and d
orbitals ● 2 in s, 6 in p, and
10 in d ● 3s23p63d10
● 18 total electrons
Fourth energy level ● s,p,d, and f
orbitals ● 2 in s, 6 in p, 10
in d, ahd 14 in f ● 4s24p64d104f14
● 32 total electrons
Electron Arrangement in Atoms
● OBJECTIVES: - Apply the Aufbau principle, the
Pauli exclusion principle, and Hund’s rule in writing the electron configurations of elements.
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Electron Arrangement = Electron Configuration
● Aufbau principle: Electrons enter orbitals of lowest energy first.
● Phosphorus (15 electrons)
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s 6s 7s
2p
3p
4p 5p 6p
3d
4d 5d
7p 6d
4f 5f
Aufbau Diagram - p. 367
or = electron
Aufbau principle: Electrons enter orbitals of lowest energy first.
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Phosphorus (15 electrons) The first two electrons go
into the 1s orbital ● Notice the opposite spins ● only 13 more to go... In
crea
sing
ene
rgy
1s
2s
3s
4s
5s 6s 7s
2p
3p
4p 5p 6p
3d
4d 5d
7p 6d
4f 5f
● The next electrons go into the 2s orbital
● only 11 more... Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s 6s 7s
2p
3p
4p 5p 6p
3d
4d 5d
7p 6d
4f 5f
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• The next electrons go into the 2p orbital
• only 5 more... Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s 6s 7s
2p
3p
4p 5p 6p
3d
4d 5d
7p 6d
4f 5f
• The next electrons go into the 3s orbital
• only 3 more... Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s 6s 7s
2p
3p
4p 5p 6p
3d
4d 5d
7p 6d
4f 5f
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Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s 6s 7s
2p
3p
4p 5p 6p
3d
4d 5d
7p 6d
4f 5f
• The last three electrons go into the 3p orbitals.
• They each go into separate shapes
• 3 unpaired electrons • = 1s22s22p63s23p3
The easy way to remember
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2
• 2 electrons
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Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2
• 4 electrons
Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
• 12 electrons
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Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2
• 20 electrons
Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2
• 38 electrons
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Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
• 56 electrons
Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
• 88 electrons
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Fill from the bottom up following the arrows
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
5f14 6d10 7p6
• 108 electrons
Exceptional Electron Configurations
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Orbitals fill in order ● Lowest energy to higher energy. ● Adding electrons can change the
energy of the orbital. ● Half filled orbitals have a lower
energy. ● Makes them more stable. ● Changes the filling order
Write these electron configurations
● Titanium - 22 electrons - 1s22s22p63s23p64s23d2
● Vanadium - 23 electrons - 1s22s22p63s23p64s23d3
● Chromium - 24 electrons - 1s22s22p63s23p64s23d4 expected
- But this is wrong!!
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Chromium is actually: ● 1s22s22p63s23p64s13d5
● Why? ● This gives us two half filled orbitals. ● Slightly lower in energy. ● The same principal applies to
copper.
Copper’s electron configuration
● Copper has 29 electrons so we expect: 1s22s22p63s23p64s23d9
● But the actual configuration is: ● 1s22s22p63s23p64s13d10
● This gives one filled orbital and one half filled orbital.
● Remember these exceptions: d4, d9
