Chapter 3 Atoms and Elements
3.7 Electron Energy Levels
1
Energy Levels
Energy levels
• are assigned numbers n = 1, 2, 3, 4, and so on.
• increase in energy as the value of n increases.
• are like the rungs of a ladder with the lower energy levels nearer the nucleus.
2
Energy Levels
Energy levels have a maximum number of electrons equal to 2n2.
Energy level Maximum number of electrons n = 1 2(1)2 = 2(1) = 2 n = 2 2(2)2 = 2(4) = 8 n = 3 2(3)2 = 2(9) = 18
3
Orbitals
An orbital • is a three-dimensional space around a
nucleus, where an electron is most likely to be found.
• has a shape that represents electron density (not a path the electron follows).
• can hold up to 2 electrons.
4
Orbitals
A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level from n = 2.
5
An s orbital
•has a spherical shape around the nucleus.
•is found in each energy level.
Orbitals
6
Electron Level Arrangement
In the electron level arrangement for the first 18
elements • electrons are placed in energy levels (1, 2, 3,
etc.), beginning with the lowest energy level• there is a maximum number in each energy
level.Energy level Number of electrons
1 2 (up to He)2 8 (up to Ne)3 8 (up to Ar)4 2 (up to Ca)
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Examples
Write the electron level arrangement for each:
1. N
2. Cl
3. K
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Examples
Identify the element with each electron level
arrangement:
1. 2, 2
2. 2, 8, 3
3. 2, 7
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Chapter 3 Atoms and Elements3.8
Periodic Trends
10
Valence Electrons
The valence electrons
• determine the chemical properties of the elements.
• are the electrons in the highest energy level.
• are related to the group number of the element.
Example: Phosphorus has 5 valence electrons. 5 valence electrons
P in Group 5A(15) 2, 8, 5
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Groups and Valence Electrons
All the elements in a group have the same number of
valence electrons.
Example: Elements in group 2A (2) have two (2) valence electrons.
Be 2, 2Mg 2, 8, 2Ca 2, 8, 8, 2Sr 2, 8, 18, 8, 2
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Periodic Table and Valence Electrons
Representative Elements Group Numbers 1 2 3 4 5 6 7
8 H He 1 2
Li Be B C N O F Ne 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8
Na Mg Al Si P S Cl Ar 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7
2,8,8
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Examples
State the number of valence electrons for each.A. O
1) 4 2) 6 3) 8
B. Al1) 13 2) 3 3) 1
C. Cl1) 2 2) 5 3) 7
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Examples
State the number of valence electrons for each. A. calcium
1) 1 2) 2 3) 3
B. group 6A (16) 1) 2 2) 4 3) 6
C. tin 1) 2 2) 4 3) 14
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ExamplesHow many electrons are in energy level 3 of
the followingA. Sulfur b.
Phosphorous
Examples
Identify the elements that have the following electron level
Energy level 1 2 3a. 2 1 0b. 2 8 6c. 2 8 7
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Electron-Dot Symbols
An electron-dot symbol• shows the valence
electrons around the symbol of the element.
• for Mg has 2 valence electrons as single dots on the sides of the symbol Mg.
. . ·Mg · or Mg · or ·Mg or
·Mg
·
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Writing Electron-Dot Symbols
Electron-dot symbols for• groups 1A (1) to 4A (14) use single dots.
· · Na · · Mg · · Al · · C ·
·
• groups 5A (15) to 7A (17) use pairs and single dots. · · · ·
· P · : O · · ·
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Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have thesame number of valence electrons (dots). Example: Atoms of elements in Group 2A (2) each have 2 valence electrons.
· Be ·· Mg ·· Ca ·· Sr ·· Ba ·
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Examples .A. X is the electron-dot symbol for
1) Na 2) K 3) Al
. .B. . X .
. is the electron-dot symbol of
1) B 2) N 3) P
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ExamplesWhat is the dot Lewis structure of
CarbonMagnesiumAluminumArgon
Atomic Size
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Atomic size is
described using the
atomic radius; the
distance from the
nucleus to the
valence electrons.
Atomic Radius Within A Group
Atomic radius increases going down each group of representative elements.
24
Atomic Radius Across a Period
Going across a period from left to right,
• an increase in the number of protons increases attraction for valence electrons.
• atomic radius decreases.
25
ExamplesSelect the element in each pair with the larger
atomicradius.
A. Li or KB. K or BrC. P or Cl
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Ionization Energy
Ionization energy is the energy it takes to remove a valence electron.
Na(g) + Energy (ionization) -> Na+(g) + e-
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Ionization Energy In a Group
Going up a group ofrepresentative
elements,
• the distance decreases between nucleus and valence electrons.
• the ionization energy increases.
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Ionization Energy
• Metals have lower ionization energies.
• Nonmetals have higher ionization energies.
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ExamplesSelect the element in each pair with the higher
ionizationenergy.
A. Li or KB. K or BrC. P or Cl
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