Physical Science Chapter 20
Chemical Bonds
1
Let’s Review:
1
1
2
3
4
5
6
7
18
2
13 14 15 16 17
Transition Elements
3 4
5
6
7 8
9 10 11 12
Check Vocabulary 20.
20:1
Stability in Bonding— Formulas
The chemical symbols Na
and Cl represent sodium and
chlorine. When written as
NaCl, this is a chemical
formula.
20:1
Stability in Bonding— Formulas
A. Some elements combine
chemically and no longer have
the same properties they did
before forming a compound.
20:1
Stability in Bonding— Formulas
A chemical formula is composed
of symbols and subscripts
indicating the number of atoms
of an element in a compound.
“Subscript” means written
below.
20:1
Stability in Bonding— Formulas
Familiar
Compounds:
Let’s look at
Table 1 on
page 603.
Add
magnesium
oxide to this
list.
Magnesium oxide
MgO (used in laxatives, antacids, fireproofing, etc.)
20:1
Stability in Bonding— Formulas
Remember: A compound is a substance
formed from two or more elements in
which the exact combination and
proportion of elements is always the
same.
20:1
Stability in Bonding— Formulas
C. Atoms form compounds
when the compound is more
stable than the separate atoms.
1. Noble gases
are more
chemically
stable than
other
elements
because they
have a
complete
outer energy
level.
20:1
Stability in Bonding— Atomic Stability
Atoms combine when the
compound formed is more
stable than the separate
atoms. Most elements can
form compounds, however
the noble gases seldom form
compounds.
19:1
Stability in Bonding— Unique Noble Gases
To understand the stability of the noble gases, you
should look at electron dot diagrams.
Pg. 604-605.
Group 1 has 1 electron in its outer shell.
Group 2 has 2 in the outer shell.
Group 13 has 3 in outer shell.
Group 14 has 4 in outer shell, etc.
Group 18 (the noble gases) has 8 in outer shell.
It is stable.
11
Title a Page in Your Notebook:
“Electron Dot Diagrams”.
1. 
Draw
2. 
electron
3. 
dot
diagram 4. 
s for
5. 
these
6. 
atoms.
7. 
Hydrogen
Carbon
Oxygen
Nitrogen
Helium
Fluorine
Argon
8. 
9. 
10.
11. 
12. 
13. 
14. 
Chlorine
Sulfur
Boron
Lithium
Neon
Sodium
Aluminum
20:1
Stability in Bonding— Unique Noble Gases
The noble gases
are stable because
they have 8
electrons in their
outer energy level.
That makes it full.
He
Kr
Ne
Xe
Ar
Rn
Lewis Theory
Between 1916 and 1919, Gilbert Newton Lewis, Walther Kossel, and
Irving Langmuir came up with a theory to explain chemical bonding. This
theory would be later called Lewis Theory and it is based on the following
principles:
Valence electrons, or the electrons in the outermost electron shell, have
an essential role in chemical bonding.
Ionic bonds are formed between atoms when electrons are transferred
from one atom to another. Ionic bond is a bond between nonmetals and
metals.
Covalent bonds are formed between atoms when pairs of electrons are
shared between atoms. A covalent bond is between two nonmetals.
Electrons are transferred/shared so that each atom may reach a more
stable electron configuration. The noble gas configuration, which contains
8 valence electrons, illustrates this principle. This is called octet rule.
Lewis Symbols and Lewis Structures
A Lewis Symbol for an element is composed of a chemical symbol
surrounded by dots that are used to represent valence electrons. An
example of a Lewis symbol is shown below with the element Carbon.
This Lewis symbol shows that carbon has four valence electrons in its outer
orbital and these four electrons play a major role in bonding of carbon
molecules.
Lewis symbols differ slightly for ions. When forming a Lewis symbol for an
ion, the chemical symbol is surrounded by dots that are used to represent
valence electrons, and the whole structure is placed in square brackets with
superscript representing the charge of the ion.
20:1
Stability in Bonding— Unique Noble Gases
2. An atom is chemically
stable when its outer
energy level is complete.
Most atoms require 8
electrons in its outer
energy level to be stable.
Remember that helium is
stable with two electrons.
Why?
20:1
Stability in Bonding— Unique Noble Gases
3. Elements that do not have
full outer energy levels are
more stable when they form
compounds.
4. Atoms can lose, gain or share
electrons to get a stable
outer energy level.
20:1
Stability in Bonding— Energy Levels
5. A chemical bond is
the force that holds
atoms together in a
compound.
20:1
Stability in Bonding— Energy Levels
Atoms form compounds when
the compound is more stable
than the separate atoms.
Na
Cl
Multiples
Sodium and Chlorine can share an electron and
each will become more stable. This new
compound is called sodium chloride,
commonly known as table salt.
Counting Atoms
complete the handout.
Compound
1.  H2O
Element Count
H
O
2
1
Total
3
20:2
Types of Bonds— A Bond Forms
A. An ion is a charged particle
because it has more or fewer
electrons than protons.
K
I
20:2
Types of Bonds— Gain or Lose Electrons
1. When an atom loses an electron,
it becomes a positively charged
ion; a superscript indicates the
charge.
2. When an atom gains an electron,
it becomes a negatively
charged ion.
20:2
Types of Bonds— The Ionic Bond
B. An ionic compound is held
together by the ionic bond —the
force of attraction between
opposite charges of the ions.
An ionic bond is formed when
an equal exchange of
electrons occurs.
20:2
Types of Bonds— The Ionic Bond
1. The result of this ionic
bond is a neutral
compound.
2. The sum of the charges on
the ions is zero.
20:2
Types of Bonds— Sharing Electrons
C. Molecules are neutral
particles formed as a result
of sharing electrons.
Particles formed from covalent
bonding of atoms are called
molecules.
20:2
Types of Bonds— Sharing Electrons
1. A covalent bond is the force of
attraction between atoms
sharing electrons.
2. Atoms can form double or triple
bonds depending upon whether
they share two or three pairs of
electrons.
20:2
Types of Bonds— Unequal Sharing
3. Electrons shared in a molecule are held
more closely to the atoms with the
larger nucleus.
4. A polar molecule has one end that is
slightly negative and one end that is
slightly positive although the overall
molecule is neutral.
20:2
Types of Bonds— Unequal Sharing
5. In a nonpolar molecule electrons are
shared equally.
Because water has a slight positive charge
at one end and a slight negative end at the
other end, it is a polar molecule.
Demonstration of water’s polarity.
20:3
Writing Formulas
A.  Chemists use symbols from the
periodic table to write formulas for
compounds.
B.  A binary compound is composed of
two elements.
In order to write formulas you need to know
which elements are involved and what
number of electrons they lose, gain, or share
in order to become stable.
20:3
Writing Formulas
1.  The oxidation number tells you
the number of electrons that are
lost, gained or shared to become
stable. The sum of the oxidation
numbers in a neutral compound
is always zero.
2.  Oxidation number is sometimes
called the valence number.
20:3
Writing Formulas
3. Use oxidation numbers and their
least common multiples to write
formulas.
a. When writing formulas,
remember that the compound is
neutral. The sum of the
oxidation numbers must equal
0.
20:3
Writing Formulas
For ionic compounds the oxidation number is
the same as the charge on the ion. For
example, a sodium ion has a charge of 1+
and an oxidation number of 1+. A chlorine ion
has a charge of 1- and an oxidation number
of 1-.
The formula SO42- stands for sulfate.
20:3
Writing Formulas
b. A formula must have
the correct number of
positive and negative
ions so the charges
balance.
20:3
Writing Formulas
4. Use the name of the first
element, the root name of the
second element, and the suffix
-ide to write the name of a
binary ionic compound.
20:3
Writing Formulas
Oxidation (Valence) Number handout
The numbers with positive or negative signs
in the handout and in Fig. 16 are the
oxidation numbers for these elements. Notice
how they fit with the periodic table groupings.
20:3
Writing Formulas
5. The elements in the PT can have more
than one oxidation number. When
naming these compounds, the oxidation
number is expressed in the name with a
Roman numeral. For example, the
oxidation number of iron in iron(III)
oxide is 3+.
20:3
Writing Formulas
C.  Polyatomic ion —positively or negatively
charged, covalently bonded group of
atoms.
1. The compound contains
three or more elements.
20:3
Writing Formulas
2. To write names, write the
name of the positive ion
first; then write the name of
the negative ion.
20:3
Writing Formulas
3. To write formulas, use the oxidation
numbers, their least common multiple,
and put parentheses around the
polyatomic ion before adding a
subscript.
20:3
Writing Formulas— Writing Names
D. Writing Names:
1.  Write the name of the positive ion.
2.  Use the tables and check to see if the
positive ion is capable of forming more
than one oxidation number. Write the
charge of the positive ion using Roman
numerals. If only one O#, go to step 3.
20:3
Writing Formulas— Writing Names
3.  Write the root name of the negative ion.
The root is the first part of the element’s
name. For chlorine the root is chlor--- for
oxygen it is ox--.
4.  Add the ending –ide to the root.
To Name Compounds
Count the Number of Elements:
If there are only 2
elements:
§  Write the name of the
first element;
§  Write the root of the
second element and…
§  Add “ide.”
If there are 3 or more
elements:
§  Write the name of the
first element or
polyatomic ion;
§  Locate the polyatomic
ion’s name on the
“Valence Sheet and write
its name.
20:3
Writing Formulas— Writing Names
Problem Solving
Activity
Write these compounds into your
notebook and name them.
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
H2O Hydrogen oxide 9.  HF Hydrogen fluoride
NaCl Sodium chloride 10. AgNO3Silver nitrate
CaI2 Calcium iodide 11. Co(NO2) 2 Cobalt nitrite
SnBr4 Tin IV bromide 12. HI Hydrogen iodide
ZnCl2 Zinc chloride 13. NH4OH
FePO4 Ferric phosphate or Ammonium hydroxide
iron III phosphate
FeS Iron II sulfide or 14. MnSO4
Ferrous sulfide
Manganese sulfate
K2O
Potassium oxide
20:3
Writing Formulas— Writing Names
E. A hydrate is a compound with water
chemically attached to its ions.
Anhydrous is a term that means
“without water.”
20:3
Writing Formulas— Writing Names
1. When writing the formula for a
hydrate it must show that the water
is chemically attached to its ions.
An example of this kind of formula
is CoCl2 6H2O.
20:3
Writing Formulas
F. Name binary covalent
compounds by using prefixes
to indicate how many atoms
of each element are in the
compound.
Writing Formulas Activity 2
Copy these compounds into your notebook and
write their balanced formula.
1.  Aluminum oxide
2.  Hydrogen iodide
3.  Hydrogen fluoride
4.  Potassium fluoride
5.  Iron II oxide
6.  Sodium bromide
7.  Tin IV bromide
8.  Copper II oxide
9.  Hydrogen oxide
10.  Sodium chloride
11.  calcium iodide
12.  zinc chloride
13.  lithium sulfide
14.  Lithium phosphate
Homework due
and test soon.