Chemical Bonding
Physical Science
Chemical Bonds
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When two or more atoms attach to each other,
they form a chemical bond
Compounds are any two elements chemically
bonded
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Water
Sugar
Salt
And almost all other substances!!!!
Electrons are responsible for the type, strength,
and size of a chemical bond
Lewis Structures
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Bohr-Rutherford diagrams are large and
difficult to show relationships between
multiple atoms
Lewis diagrams are used to show multiple
atoms
Lewis diagrams show only the valence
electrons
Lewis Structures
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Valence electrons form the charge of an
atom
Electrons are always trying to get together
in groups of 8 (forget shells for a minute)
Elements that have 8 valence electrons
have FULL outer groups
We call these elements NOBLE or INERT
gases, they are found in group 8
Lewis Structures
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Label the Nobel (Inert) gases on your chart
Lewis Structures
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Elements with 1 valence electron are called the
Alkali metals (group 1) (Label)
Lewis Structures
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Elements with 2 valence electrons are called the
Alkaline Earth metals (group 2) (Label)
Lewis Structures
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Elements with 7 valence electrons are called the
Halogens (group 7) (Label)
Lewis Structures
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Consist of
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Element Symbol
Electrons in each open spot
Sy
Lewis Structures
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7
Draw the element symbol
Determine the # valence electrons
Starting at the top, going clockwise, place one
electron in each spot around the element symbol
Cl
Lewis Structure
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Draw the Lewis Structure for Aluminum!
Al
Quick Recap!
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Draw the Lewis Structure for Lithium!
Draw the Rutherford-Bohr Diagram for
Lithium!
-
Li
3P
3N
-
A note about charges…
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Writing a charge
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Valence electrons, Bohr-Rutherford, and Lewis
diagrams are used to determine charge
Charges are a shortcut to determining bonding
properties
RULES OF CHARGE
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IF the # of valence electrons is GREATER than 4, the charge
is negative (Mostly)
IF the # of valence electrons is less than 4, the charge is
positive (Mostly)
Charges are in reference to a full shell of 8
A note about charges…
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For example, Aluminum has 3 valance
electrons
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The possible charges are +3 OR -5
It either has 3 OVER a full shell, or 5 LESS
than a full shell
Because the number 3 is less than 4, we use
the charge of +3
Charges
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Any element with a
charge is called an
ION, the charge is an
ionic charge
What are the ionic
charges of the
elements in the table?
Sodium?
+1
Nitrogen? -3
Oxygen?
-2
Argon?
0
Charges
Charges
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A few exceptions!
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Metals are always a positive charge!!
Non metals are always negative!!
Metalloids can go either way (you are not
responsible for choosing – I will tell you)
Example: Boron
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According to rule of 4’s….its a +3 charge
But since it’s a nonmetal, we use -5!
Rules of Bonding
1.
2.
3.
4.
All compounds must have neutral
charges
(That means the positive charges
(cations) and the negative charges
(anions) must equal
Subscript numbers are used to show the
number of ions
Coefficients are used to show the
number of molecules
Rules of Bonding
2H2O
Coefficient
Subscript
1 atom of O
“1’s” are
implied and
not written
Subscript
2 atoms of H
Rules of Bonding
H2O
H
H
O
Rules of Bonding
H2O
O
H
H
Rules of Bonding
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Try this one!
NaCl (table salt)
Na Cl
Rules of Bonding
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Last One!
Aluminum Bromide
Br Al Br
Br
Chemical Bonding
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Several Types including
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Covalent Bonds*
Ionic Bonds*
Metallic (only between metals)
Covalent Bonds
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Electrons are shared between two or more
atoms
Covalent bonds can exist between atoms of the
same type…for example N-N (N2) or O-O (O2)
Covalent bonds can form single, double, or triple
bonds
Covalent bonds are strong and usually result in
stable molecules
Carbon always forms covalent bonds and forms
the basic molecules for all life substances
Ionic Bonds
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Usually formed by members of the Alkali
group (ones with +1 electron)
Electrons are donated to another molecule
Between elements from opposite sides of
the chart
Forms crystals (salts) & most dissolve in
water
Forming Compounds
1.
2.
3.
4.
Write ions with charges
Cross charges
Write subscripts (omit “1’s”)
Use parenthesis if needed
Forming Compounds
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What is the molecular formula of water?
+1
H
H2
-2
O
O1
H2O
O
H
H
Forming Compounds
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What is the molecular formula of carbon
dioxide?
+4
-2
C
O
C2
O4
C2O4
CO2
Yikes!
Reduce like a fraction to
lowest denominator
****note****
Forming Compounds
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What is the molecular formula of a
compound that has aluminum and
sulphur?
+3
-2
Al
S
Al2 S3
Al2S3
Any guesses
on the
name?