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Chapter 8
Chemical Bonding
Section 1
Electrons
• A chemical bond is
the joining of atoms to
form new substances
with new properties
– Compounds will not
have the same
properties as the
elements that went
into them
1. Electrons are the
key as chemical
bonding involves the
interaction of certain
electrons (valence).
2. Atoms are most
stable when their
outer energy level is
full.
Which group has elements that already
have a full outer energy levels?
Valence Electrons
• Valence electrons
refer to the electrons
on the outer-most
electron level.
• These are the only
electrons involved in
a chemical reaction.
• Atoms will be most
stable if they have a
full outer energy level.
• Some atoms will lose
electrons,…
Na
8
8
2
Sodium
11
protons
Valence Electrons
• Valence electrons
refer to the electrons
on the outer-most
electron level.
• These are the only
electrons involved in
a chemical reaction.
• Atoms will be most
stable if they have a
full outer energy level.
• Some atoms will lose
electrons, other will
gain electrons.
S
8
8
2
Sulfur
16
protons
3. Only valence electrons are involved in chemical bonding.
• Valence electrons are
the outer-most
electrons
– There are only 8 electrons
that are valence.
Group 1 = 1 valence electron
Group 2 = 2 valence electrons
Group 18
Group 17
Group 16
Group 15
Group 14
Transition Metals
Group 13
Group 2
Group 1
Groups 3-12
Group 13 = 3 valence electrons
Group 14 = 4 valence electrons
Group 15 = 5 valence electrons
Group 16 = 6 valence electrons
Group 17 = 7 valence electrons
Group 18 = 8 valence electrons
(full)
There is no rule for
the valence
electrons of
Transition Metals.
Some have one,
others two or three.
Electron Dot Diagrams
• Electron Dot
Diagrams can be
used to represent
how many valence
electrons there are for
each atom
• Follow the pattern
1
5
8
2
E
4
7
3
6
• For example…
B
N
O
• Special Exceptions…
He
C
Types of Chemical Bonds:
1.
Ionic Bonds
• Ionic bond is the force of
attraction between
oppositely charged ions
– Ions are atoms that have
lost or gained electrons in a
chemical reaction.
– The positive ion and the
negative ion form a neutral
compound.
• Examples of ionic bonds
– Salt (NaCl)
– Plaster (cast)
– Seashells (calcium
carbonate)
• Ions
– Through chemical
reactions atoms may gain
or lose electrons
– Ions are charged particles
• Positive ions have lost one or
more electrons
• Negative ions have gained
one or more electrons
Lithium ion (Li+) has
lost one electron
(should have three)
3 positive protons
2 negative electrons
Oxygen ion (O-2)
has gained two
electrons (should
have eight)
8 positive protons
When an alkali metal reacts
with a halogen it forms a salt
10 negative electron
For example
• Ions are identified by
their oxidation
numbers
Li+
+2
Ca
+3
Al
-3
N
-2
S
Br
Oxidation numbers represent the number of
electrons lost or electrons gained, written above
and to the right of the symbol
Lost one electron
Lost two electrons
Lost three electrons
Gained three electrons
Gained two electrons
Gained one electron
Positive Ions
Group Name
Valence
Electrons
Gain/lose
Oxidation
number
Group 1
Alkali Metal
1
Lose
+1
Group 2
Alkaline Earth
Metal
2
Lose
+2
Group 13
Boron
3
Lose
+3
Losing Electrons in chemical reactions is Endothermic.
Making Positive Ions
• Positive ion (metals)
– Ions where electrons have
been lost
Sodium is an alkali metal, having
one valence electron
In a chemical reaction it will lose
that electron.
– Example Sodium
+
Na
Na
Sodium becomes a positive ion
after a chemical reaction
because it has more protons
than electrons.
Notice:
P
CHEMICAL
11+
REACTION
Atoms require extra energy to
remove electrons (losing
10 - electrons electrons is endothermic)
11 + protons
+++++++++++
-----------
• Example aluminum
Notice:
+3
Al
Al
• Aluminum is a group 13
atom, having 3 valence
electrons.
13 + protons
10 - electrons
P
CHEMICAL
13+
REACTION
• During a chemical
reaction aluminum will
lose 3 electrons
• Aluminum becomes a
positive ion because it
has more protons than
electrons.
Negative Ions
Group Name
Valence
Electrons
Gain/lose
Oxidation
number
Group 15
Nitrogen
5
Gain
-3
Group 16
Oxygen
6
Gain
-2
Group 17
Halogen
7
Gain
-1
Gaining Electrons in chemical reactions is Exothermic.
Making Negative Ions
• Negative ions (nonmetals)
– Ions where electrons have
been gained
– Add an “ide” ending to show
which atoms have gained
electrons
– Example chlorine
Notice:
17 + protons
Cl
Cl
18 - electrons
CHEMICAL
P
REACTION
• Chlorine is a halogen (group
17) , having 7 valence
electrons.
• Chlorine, a nonmetal, will gain
electrons in a chemical
reaction.
• It will become a negative ion
because it has more electrons
than protons after a chemical
reaction.
+++++++++++++++++
• Gaining electrons releases
- - - - - energy
-exothermic).
- - (-gaining
- - -electrons
- - - is- - -
17+
Chlorine becomes chloride
• Oxygen is a group 16
atom, having 6 valence
electrons.
– Example oxygen
• Oxygen, a nonmetal, will
gain 2 electrons in a
chemical reaction.
Notice:
8 + protons
-2
OO
10 - electrons
CHEMICAL
P
REACTION
• It will become a negative
ion because it has more
electrons than protons
after a chemical reaction.
8+
Oxygen becomes oxide
Metals lose electrons
in chemical reactions
Metals become
positive ions in
chemical reactions
+1 +2
+1 +2
+1 +2
+1 +2
+1 +2
+1 +2
+3
+3
+3
+3
+3
+3
Nonmetals gain electrons
in chemical reactions
Nonmetals become
negative ions in
chemical reactions
+2
+2
+2
+2
+2
+2
+3
+3
+3
+3
+3
+3
-4 -3 -2 -1
-3 -2 -1
-2 -1
+4
-1
+4
-1
+4
•
•
Positive and negative
ions will attract each
other
Ionic bonds have the
following properties
1. High melting/boiling
points (strong bonds)
2. Form crystal lattices
3. Brittle
Na+
Cl-
Covalent Bonds
• A covalent bond
involves the sharing
of electrons to form
molecules
– Electrons are not
exchanged (ions are
not formed)
– Nonmetals
– Properties
1. Low melting and
boiling points
2. brittle when solid
• Examples
–
–
–
–
Water (H2O)
Carbon dioxide (CO2)
Sugar (C6H12O6)
Diatomic molecules
• Elements that are found
in pairs when not part of a
compound, never alone
• There are 8 of them
(H2, N2, O2, Group 17)
No, really…..
•DIATOMIC
I2
Br2
H2
At2
N2
O2
Cl2 F2
•
•
•
•
Hydrogen
Nitrogen
Oxygen
Group 17
–
–
–
–
–
Fluorine
Chlorine
Bromine
Iodine
Astatine
Diatomic molecules are formed because certain elements
react so easily they automatically combine with each other
when they are in their gaseous state.
H2
H +
H
H
H
HHH HHH
Cl2
Cl
+
Cl
Cl
Cl
Cl
Cl Cl
ClCl
Other Covalent Molecules
Water (H2O)
H
O
O
H
OH
H
+
-
Metallic Bonds
• Metallic bond is the
force of attraction
between positive
metal ions and the
loose valence
electrons in a metal
– Valence electrons can
easily travel from one
atom to the next
because of
overlapping
electron rings
Fe
+
Fe
(Iron i
(Iron ion)
+
Fe
(Iron ion)
• The properties of metals
are explained by metallic
bonds
– Malleabililty/ductility
because the atoms are not
locked to one single atom
– Conducting heat/electricity
because electrons can
move freely or can be
forced to move in one
direction
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
• Electrons can be made to travel in one
direction
WIRE
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
Au
WIRE