chapter 2 atoms and elements
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Chapter 2 Atoms and Elements. Electron Arrangement and Periodic Law. Characteristics of Electrons. Extremely small mass Located outside the nucleus Moving at extremely high speeds in a sphere Have specific energy levels. Energy of Electrons. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 2
Atoms and ElementsElectron Arrangement and
Periodic Law
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Characteristics of Electrons
Extremely small mass
Located outside the nucleus
Moving at extremely high speeds in a
sphere
Have specific energy levels
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Energy of Electrons
When atoms are heated, bright lines appear
called line spectra
Electrons in atoms arranged in discrete
levels.
An electron absorbs energy to “jump” to a
higher energy level.
When an electron falls to a lower energy
level, energy is emitted.
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Loss and Gain of Energy
GaIn
Loss
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Learning Check EA1
Answer with
1) Energy absorbed 2) Energy emitted
3) No change in energy
A. What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?
B. What energy change takes place when the electron moves from the third shell to the second shell?
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Solution EA1
A. 1) Energy absorbed
B. 2) Energy emitted
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Bohr Model
• First model of the electron structure
• Gives levels where an electron is most likely to be found
• Incorrect today, but a key in understanding the atom
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Quantum Mechanics
Describes the arrangement and space occupied by electrons in atoms
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Electron Levels (Shells)
Contain electrons that are similar in
energy and distance from nucleus
Low energy electrons are closest to the
nucleus
Identify by numbers 1, 2, 3, 4, 5, 6…..
The first shell (1) is lowest in energy, 2nd
level next and so on 1<2<3<4
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Number of Electrons
Maximum number of electrons in any electron level = 2n2
n =1 2(1)2 = 2
n =2 2(2)2 = 8
n =3 2(3)2 = 18
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Order of Electron Filling
All electrons in the same energy level have similar energy.
Shell 1 2 electrons
Shell 2 8 electrons
Shell 3 18 electrons (8 first, later 10)
Order of filling for the first 20 electrons
Shell 1 2 3 42e 8e 8e 2e
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Electron Configuration
Lists the shells containing electronsWritten in order of increasing energy
Element Shell 1 2 3
He 2
C 2 4
F 2 7
Ne 2 8
Al 2 8 3
Cl 2 8 7
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Learning Check EA2
A. The electron configuration for sulfur
1) 2,6 2) 8,2,6 3) 2, 8, 6
B. The element in period 3 with two electrons in the outermost energy level
1) Mg 2) Ca 3) Be
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Solution EA2
A. The electron configuration for sulfur
3) 2, 8, 6
B. The element in period 3 with two electrons in the outermost energy level
1) Mg
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Learning Check EA3
Indicate the number of electrons in the final notation of the electron configuration for each:
A. O 1) 4 2) 6 3) 8
B. Al 1) 13 2) 3 3) 1
C. Cl 1) 2 2) 5 3) 7
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Solution EA3
Indicate the number of electrons in the final notation of the electron configuration for each:
A. O 2) 6
B. Al 2) 3
C. Cl 3) 7
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Learning Check EA4
For phosphorus, indicate if each configuration is (1) correct or (2) incorrect. Explain why or why not?
A. 2, 2, 8, 5 1 or 2
B. 2, 8, 3 1 or 2
C. 2, 8, 5 1 or 2
D. 2, 6, 7 1 or 2
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Solution EA4
For phosphorus, indicate if each configuration is (1) correct or (2) incorrect. Explain why or why not?
A. 2, 2, 8, 5 2 Shell 2 holds 8e-
B. 2, 8, 3 2 P has 15 electrons
C. 2, 8, 5 1 Correct arrangement
D. 2, 6, 7 2 Shell 2 holds 8e-
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Periodic Law
All the elements in a group have the same electron configuration in their outermost shells
Example: Group 2
Be 2, 2
Mg 2, 8, 2
Ca 2, 2, 8, 2
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Learning Check EA5
Specify if each pair has chemical properties that are similar (1) or not similar (2):
A. Cl and Br
B. 2 - 5 and 2 - 8 - 7
C. 2 - 4 and 2 - 8 - 4
D. P and S
E. O and S
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Solution EA5
Specify if each pair has chemical properties that are similar (1) or not similar (2):
A. Cl and Br 1
B. 2 - 5 and 2 - 8 - 7 2
C. 2 - 4 and 2 - 8 - 4 1
D. P and S 2
E. O and S 1