Transcript Chapter 3 Atoms and Elements

Chapter 3 Atoms and Elements
3.7
Electron Energy Levels
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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.
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Energy Levels
Energy levels have a maximum number of electrons equal
to 2n2.
Energy level
n=1
n=2
n=3
Maximum number of electrons
2(1)2 = 2(1) = 2
2(2)2 = 2(4) = 8
2(3)2 = 2(9) = 18
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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.
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Orbitals
An s orbital
•has a spherical shape around the nucleus.
•is found in each energy level.
A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level from n = 2.
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Orbitals
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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 Elements
3.8
Periodic Trends
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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, 2
Mg
2, 8, 2
Ca
2, 8, 8, 2
Sr
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
1
Li
2,1
Be
2,2
B
2,3
C
2,4
Na
Mg Al Si
2,8,1 2,8,2 2,8,3 2,8,4
F
2,7
He
2
N
2,5
O
2,6
Ne
2,8
P
2,8,5
S
Cl
Ar
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.
C.
Al
1) 13
2) 3
3) 1
Cl
1) 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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Examples
 How many electrons are in energy level 3 of the
following
 A. Sulfur
b.
Phosphorous
Examples
Identify the elements that have the following
electron level
Energy level
1
2
3
a.
2
1
0
b.
2
8
6
c.
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 the
same 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
B.
..
.X.
.
1) B
2) K
3) Al
is the electron-dot symbol of
2) N
3) P
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Examples
 What is the dot Lewis structure of
 Carbon
 Magnesium
 Aluminum
 Argon
Atomic Size
Atomic size is described
using the atomic radius;
the distance from the
nucleus to the valence
electrons.
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Atomic Radius Within A Group
Atomic radius increases
going down each group of
representative elements.
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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.
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Examples
Select the element in each pair with the larger atomic
radius.
A. Li or K
B. K or Br
C. 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 of
representative 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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Examples
Select the element in each pair with the higher ionization
energy.
A. Li or K
B. K or Br
C. P or Cl
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