Chemical bonding involves the attraction between atoms that forms as a result of interactions between valence electrons. There are three main types of bonds: ionic bonds result from the transfer of electrons between metals and nonmetals, covalent bonds involve sharing of electrons between nonmetals, and metallic bonds are attractions between positive metal ions and delocalized electrons in metals. The number of valence electrons determines an element's chemical properties and how it bonds. Chemical reactions occur through the breaking and forming of new bonds, and equations are used to represent these processes in a balanced way that obeys the law of conservation of mass.

1. Chemical
Bonding

2. Chemical Bond
 A force of attraction that holds two atoms
together
 Has a significant effect on chemical and
physical properties of compounds
 involves the valence electrons
Valence Electrons – the electrons
in the outermost energy level of an
atom
-
This Lithium
Atom has one
valence electron
+
-
+ +
-

3. Counting Valence Electrons
-
-
-
+
-
+
+
+
-
-
+
-
++ +
+ + +
+
+
-
+
-
-
-
+
-
+ +
-
+
-
-
-
Carbon
Oxygen
Beryllium
4 valence
electrons
6 valence
electrons
2 valence
electrons

4. How Many Valence Electrons?
 Hydrogen
 Lead
 Xenon
 Sulfur
 Sodium
1 Valence
Electron
4 Valence
Electrons
8 Valence
Electrons
6 Valence
Electrons
1 Valence
Electron

5. The Octet Rule
 Atoms will combine to form compounds in
order to reach eight electrons in their
outer energy level.
 Atoms with less than 4 electrons tend to lose
electrons.
 Atoms with more than 4 electrons tend to gain
electrons.
 Be aware that there are some exceptions!
CONSIDER EIGHT A HAPPY NUMBER FOR
ATOMS!

6. The Octet Rule In Action
6
-
7
-
-
-
5
Notice how this chlorine atom
has seven valence electrons,
one away from eight. It will try
to gain one more according to
the Octet Rule.
-
-
-
+
+
++ +
++
+
+ + ++
+
++ ++
-
4
-
-
1
-
3
-
-
-
-
-
1
-
-
-
2
Notice how the sodium atom has
one valence electron. It is this
electron that it will try to get rid of
according to the Octet Rule.
-
+ ++
+ + +
+ +
++ +
-
-
-
-
Where do you think Chlorine finds that one electron that it needs?

7. Lewis Structure
(Electron Dot Diagram)
 a way of drawing the outer energy level
electrons (valence) of an atom
 The symbol for the element surrounded
by as many dots as there are electrons in
its outer energy level (valence)
 Examples
Al :
Aluminum
.
.N :
.
.
Nitrogen
Mg :
Magnesium
How many valence electrons do each of these atoms have?

8. Making an Electron Dot Diagram
Element “X” has 8 valence electrons
Write down the element’s symbol
and place the first two dots on any
side of the symbol.
.
X
X:
1
If this were an atom of an element
from group 1, you would just place the
one dot on any side of the element.
.
.X :
.
4
..
.X :
.
5
.
X:
2
.
.X :
3
Place the rest of the dots in either a
clockwise or counter clockwise manner around
the symbol, with no side receiving two dots
until each side gets one.
..
:X:
.
6
..
:. .:
X
7

9. What Would the Electron Dot
Diagram Look Like?
1 Valence Electron
6 Valence Electrons
H
O
How many valence
electrons does
each atom have?
Ne
8 Valence Electrons
Sr
2 Valence Electrons

10. Oxidation Number
 The charge that an atom would have if it lost
or gained electrons; ionic charge
 Can be helpful in determining which atoms
will interact or bond with each other
 Example:
According to electron dot diagram for Magnesium, it
has two valence electrons. Because Magnesium is
“unhappy” with two, it will typically lose them. If this
happens it will turn into a Magnesium ion. At this
point it will have an oxidation number of +2.
Mg :
Magnesium
2+
Mg

11. What Could the Oxidation Number Be?
H
+1 or -1 because it can
gain or lose one electron
Ne
0 because it will not
gain or lose electrons
O
-2 because it will
gain two electrons
Sr
+2 because it will
lose two electrons

12. 3 Types of Chemical Bonds
Ionic
Covalent
Metallic
What can you describe about each of these
bonds just by looking at the name?

13. IONIC BONDS
 The force of attraction between oppositely charged ions.
 Occurs after a transfer or loss/gain of electrons
 Usually form between atoms of metals and atoms of non-
metals
 Resulting compounds have a name that usually ends in –
ide
Cl 1-
-
Na 1+
-
-
-
-
-
-
-
-
++ +
+ + +
+
+
-
-
-
++ +
+ + +
+
+
- -
-
-
-
-
-
-
-
-
Example - Sodium Chloride (NaCl)
Which
different
groups or
families
of elements
will mostlikely
interact to
create these
types
of bonds?

14. COVALENT BOND
 A force that bonds two atoms together by a sharing of
electrons
 Each pair of shared electrons creates a bond
 Usually occurs between atoms of non-metals
H O H
-
-
+
-
++ +
+ + +
+ +
-
-
+
-
Example – Water (H2O)

15. Types of Covalent Bonds
 Different covalent bond types share a different
number of electrons
Water (H2O)
-
Carbon Dioxide (CO2)
Nitrogen (N2)
-
-
-
-
+
++ +
+ +
+
+
+
+
++ +
+ +
+
+
- - -
++
+ +
+
+
- - -
++ +
+ + +
+
+
+
++
+
+ +
+
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- - -
++
+ + +
+
+
-
-
-
-
-
- -
-
+
Single Bonds
Share 2
Electrons
Double Bonds
Share 4
Electrons
Triple Bonds
Share 6
Electrons

16. Metallic Bond
 A force of attraction between a positively charged metal ion and the
electrons in a metal
 Many metal ions pass along many electrons
 Many properties of metals, such as conductivity, ductility, and
malleability, result from the freely moving electrons in the metal
 Usually occurs between atoms of metals
Al3+
Al3+
-
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
- Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
-
Al3+
Al
- 3+
Al3+
- Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
Al3+
-
-
-
Al3+
Al3+
Al3+
- Al3+
-
Al3+
Al3+
Al3+
- Al3+
Al3+
Al3+
Notice
how the
electrons
do not just
stay with
one ion

18. Unequal Sharing
(Polar Covalent Bond)
 The unequal sharing of electrons between two atoms that gives
rise to negative and positive regions of electric charge
 Results from an atom’s electronegativity – the ability to attract
electrons to itself
+
+
Bonded hydrogen
atoms showing
equal sharing of
electrons
Electron
Cloud
++ +
+ + +
+ +
+
Hydrogen and
fluorine bond with
an unequal sharing
of electrons
Why do you think the two Hydrogen atoms share
equally, but the Hydrogen and fluorine do not?

19. Results of Bonding
Molecule
A neutral group of two or more
non-metal atoms held together
by covalent bonds
Type:
Diatomic - molecules consisting
of two atoms of the same
element bonded together
Examples:
H2, F2, O2, N2
Compound
A pure substance composed of
two or more different elements
(atoms) that are chemically
combined
Examples:
CO, NO2, NaCl
What would you call something that has
characteristics of both?

20. Molecule, Compound, or Both?

21. Chemical Reaction
 The process by which a chemical
change occurs
 Atoms are rearranged, and
chemical bonds are broken and
reformed
 One or more substances change to
produce one or more different
substances
 Types




What does
H2 & O2 gas
create?
Synthesis (creating)
Decomposition (separating)
Combustion (burning)
Displacement/Replacement
(switching)
Out of the four types of reactions, which
would describe the chemical reaction
taking place to the right?
H2
O2

22. Physical Change
 a change in shape, size, color, or state
 a change without a change in chemical composition
 a change that is reversible
 The Mixtures Lab
Examples
tearing paper
cutting your hair
change in state
Physical
changes are
not indicative
of a chemical
reaction

23. Chemical Change
 a change in which a substance becomes another
substance having different properties
 a change that is not reversible using ordinary physical
means
 Changes that usually cause, heat, sound, light, odor,
fizzing/foaming, color changes
You usually need more than one of the above characteristics to be
considered a chemical change!
Examples
mixing vinegar & baking soda
burning a piece of wood
soured milk
A chemical analysis is the only 100% way to know a
chemical change has occurred.

24. Chemical Equation
 Shorthand form for writing what reactants are used
and what products are formed in a chemical reaction
 Sometimes shows whether energy is produced or
absorbed
 Examples:
2H2 + O2  2H2O
CH4 + 2O2  CO2 + 2H2O
C6H12O6 + 6O2  6CO2 + 6H2O + energy

25. Components of a Chemical Equation
Chemical
Formulas
2H2 + O2
Chemical
Formula

2H2O
Subscript
Coefficient
Coefficient
(Yield)
(Reactants)
(Products)
Sometimes you will see a “yields” sign that looks like this.
What do you think it means?





Subscripts

26. Energy and Chemical Reactions
Exothermic Reaction
Endothermic Reaction
 A chemical reaction in which
 A chemical reaction in which
energy is released.
 The products have greater
bond energy than the
reactants
energy is absorbed.
 The products have lower
bond energies than the
reactants
C6H12O6 + 6O2  6CO2 + 6H2O + energy
(respiration)
6CO2 + 6H2O + energy  C6H12O6 + 6O2
(photosynthesis)
Chemistry Comes Alive! Sample Movies
TeacherTube - Videos
Chemistry Demonstration Videos
Can you think of other reactions where
energy is gained or released?

27. Rates of Chemical Reactions
The rates at which chemical reactions can take place are
based on the interaction (collisions) between the different
particles. These rates can be impacted by the following:
 Temperature –a measure of the average kinetic energy of the
particles in a sample of matter
 Ex. Increasing the temperature when cooking
 Surface area – amount of material that comes into contact
with the reactants
 Ex. Cutting a potato into smaller pieces when cooking
 Concentration – amount of substance per volume
 Ex. Turning the valve on a gas stove to increase the concentration
of methane molecules
 Catalysts (enzymes) – organic substances that help speed up
chemical reactions, but are not consumed in the reaction

28. Law of Conservation of Mass
 Proposed by Antoine Lavoisier
 In a chemical reaction, atoms are neither created nor
destroyed
 All atoms present in the reactants are also present in the
products
 Chemical equations must account for/show the conservation
of mass  balancing equations
In its present form, does this chemical equation show a
conservation of mass?
2 H2 + O2  2 H2O
Reactants
H  24
O  22
Products
How would you balance this equation to
show the conservation of mass?
H  24
O  12

29. Hints For Balancing Equations
 Count the atoms
 List the number of atoms of each element to see which
elements must be balanced
 Use a coefficient to add atoms to one side of the equation
 Start with the reactant or product that has the greatest
number of different elements
 Add a coefficient to another reactant or product
 Make sure that the coefficients in your balanced equation are
the smallest whole numbers possible (they should have no
common factor other than one)
Tutorial on Balancing Equations