Chemical Bonding
PRENTICE HALL PHYSICAL SCIENCE
CHAPTER 6 SECTIONS 1 AND 2
Day 1 – Key Points
When is an atom unlikely to react?
What is one way in which elements can
achieve stable electron configurations?
 How does the structure of an ionic
compound affect its properties?
Electron dot diagrams
 A model of an atom in which each dot represents a valence
electron.
 The symbol in the center represents the nucleus and other
electrons.
Stable Electron Configurations
 Noble gases are the most stable elements.
•
Eight valence electrons (two electrons in the case of
helium).
• Elements react to achieve electron stability
• Eight valence electrons
IONIC BONDS
►Bonding through the transfer of
electrons.
Ions
►An atom that has a net positive or negative electric
charge is called an ion.
►The atom losing electrons forms a positive ion
(a cation) and is usually a metal.
►The atom gaining electrons forms a negative
ion (an anion) and is usually a non-metallic
element.
Figure 2-3 Ionic Bonding
Section 2-1
Sodium atom (Na)
Chlorine atom (Cl)
Sodium ion (Na+)
Chloride ion (Cl-)
Transfer
of electron
Protons +11
Electrons -11
Charge
0
Protons +17
Electrons -17
Charge
0
Protons +11
Electrons -10
Charge
+1
Protons +17
Electrons -18
Charge
-1
Figure 2-3 Ionic Bonding
Section 2-1
Sodium atom (Na)
Chlorine atom (Cl)
Sodium ion (Na+)
Chloride ion (Cl-)
Transfer
of electron
Protons +11
Electrons -11
Charge
0
Protons +17
Electrons -17
Charge
0
Protons +11
Electrons -10
Charge
+1
Protons +17
Electrons -18
Charge
-1
Ionic Bonds
1. Using Tables Within a
period, what happens to the
atomic radius as the atomic
number of the elements
increases?
Ionic Bonds
1. Using Tables Within a
period, what happens to the
atomic radius as the atomic
number of the elements
increases?
Answer: Within a period,
the atomic radius decreases
as the atomic number
increases.
Ionic Bonds
2. Using Tables
Within Groups 1A, 2A,
6A, and 7A, what
happens to the atomic
radius of elements as
the atomic number
increases?
Ionic Bonds
2. Using Tables
Within Groups 1A, 2A,
6A, and 7A, what
happens to the atomic
radius of elements as
the atomic number
increases?
Answer: Within these
groups, the atomic
radius increases as the
atomic number
increases.
Ionic Bonds
3. Inferring How does
adding an occupied energy
level affect the atomic
radius? (Hint: Lithium is a
Period 2 element and
sodium is a Period 3
element.)
Ionic Bonds
3. Inferring How does
adding an occupied energy
level affect the atomic
radius? (Hint: Lithium is a
Period 2 element and
sodium is a Period 3
element.)
Answer: When the next
higher energy level is
occupied, there is a
significant increase in
atomic radius.
Ionic Bonds
4. Comparing and
Contrasting Compare the
atomic and ionic radii for
potassium (K), and for
bromine (Br).
Ionic Bonds
4. Comparing and
Contrasting Compare the
atomic and ionic radii for
potassium (K), and for
bromine (Br).
Answer: The ionic radius
for potassium is much
smaller than its atomic
radius. The ionic radius for
bromine is much larger
than its atomic radius.
Ionic Bonds
5. Making
Generalizations What
happens to the radius of an
atom when the atom loses
electrons? When the atom
gains electrons?
Ionic Bonds
5. Making
Generalizations What
happens to the radius of an
atom when the atom loses
electrons? When the atom
gains electrons?
Answer: With the loss of
valence electrons, the
radius decreases. With the
addition of valence
electrons, the radius
increases.
Ionic Bonds
6. Relating Cause
and Effect Explain the
difference in size
between a metal atom
and its cation.
Ionic Bonds
6. Relating Cause
and Effect Explain the
difference in size
between a metal atom
and its cation.
Answer: An energy level
that was occupied is no
longer occupied, and
the size decreases.
Ionization Energy
 Electrons must gain enough energy to escape their
attraction to protons
 The amount of energy used to remove an electron is called
ionization energy
 The lower the ionization energy the easier to remove an
electron
Chemical Formula
 a notation that shows what elements a compound
contains and the ratio of the atoms or ions of those
elements in the compound
What is the chemical formula for magnesium chloride?
Ionic Compounds – Chemical Formulas
What is the chemical formula for magnesium chloride?
Ionic Compounds – Chemical Formulas
What is the chemical formula for magnesium chloride?
Ionic Compounds
What is the chemical formula for magnesium chloride?
A magnesium atom cannot reach a stable electron configuration by
reacting with just one chlorine atom. It must transfer electrons to two
chlorine atoms. After the transfer, the charge on the magnesium ion is
2+ and its symbol is Mg2+.
Ionic Compounds - Structure
The structure and shape of a crystal are related:
A. In a sodium chloride crystal, each ion is surrounded by
six oppositely charged ions.
B Sodium chloride crystals are shaped like cubes
Structure depends on the ratio of ions and their
relative sizes. Crystals are classified into groups
based on the shape of their crystals.
Properties of Ionic Compounds
The properties of sodium chloride are
typical of ionic compounds.
•
•
•
Sodium chloride has a high melting point
(801°C).
Solid sodium chloride is a poor
conductor of electric current. When
melted, it is a good conductor of
electric current.
Sodium chloride crystals shatter when
struck with a hammer.
Assessment Questions
1.
When is an atom stable?
a.
b.
c.
d.
when its electrons are evenly distributed through its
energy levels
when its lowest occupied energy level is filled with
electrons
when its highest unoccupied energy level is filled with
electrons
when its highest occupied energy level is filled with
electrons
Assessment Questions
1.
When is an atom stable?
a.
b.
c.
d.
when its electrons are evenly distributed through its
energy levels
when its lowest occupied energy level is filled with
electrons
when its highest unoccupied energy level is filled with
electrons
when its highest occupied energy level is filled with
electrons
ANS: D
Assessment Questions
2. Which description applies to an element that has
two valence electrons?
a.
b.
c.
d.
reactive metal
nonreactive metal
reactive nonmetal
nonreactive nonmetal
Assessment Questions
2. Which description applies to an element that has
two valence electrons?
a.
b.
c.
d.
reactive metal
nonreactive metal
reactive nonmetal
nonreactive nonmetal
ANS: A
Assessment Questions
3. How do sodium and chlorine both achieve stable
electron configurations when they react?
a.
b.
c.
d.
An electron is transferred from the sodium atom to the
chlorine atom.
An electron is transferred from the chlorine atom to the
sodium atom.
Both atoms gain one electron.
Both atoms lose one electron.
Assessment Questions
3. How do sodium and chlorine both achieve stable
electron configurations when they react?
a.
b.
c.
d.
An electron is transferred from the sodium atom to the
chlorine atom.
An electron is transferred from the chlorine atom to the
sodium atom.
Both atoms gain one electron.
Both atoms lose one electron.
ANS: A
Assessment Questions
4.
Why do ionic compounds tend to have high melting
points?
a.
b.
c.
d.
Ionic compounds contain more than one element, which causes a
high melting point.
Ionic compounds cannot absorb energy efficiently because they
contain ions.
An ionic compound contains metal atoms that raise its melting
point.
A strong electrical attraction means ions require a lot of energy to
move apart.
Assessment Questions
4.
Why do ionic compounds tend to have high melting
points?
a.
b.
c.
d.
Ionic compounds contain more than one element, which causes a
high melting point.
Ionic compounds cannot absorb energy efficiently because they
contain ions.
An ionic compound contains metal atoms that raise its melting
point.
A strong electrical attraction means ions require a lot of energy to
move apart.
ANS:
D
Assessment Questions
1.
The ratio of aluminum ions to chloride ions in
aluminum chloride (AlC13) is 3:1.
True
False
Assessment Questions
1.
The ratio of aluminum ions to chloride ions in
aluminum chloride (AlC13) is 3:1.
True
False
ANS:
F, 1:3
Day 2 – Key Questions
How are atoms held together in a covalent bond?
 What happens when atoms don’t share electrons
equally?
When atoms form a polar covalent bond, the atom
with the greater attraction for electrons has a partial
negative charge. The other atom has a partial
positive
How do attractions between polar molecules
compare to attractions between nonpolar molecules?
COVALENT BONDS
►When 2 elements share one or
more electrons
►Occurs between nonmetals
►Form molecules
►strong bond
►ex. CO2
Covalent Bonds
There are several ways to show a covalent
bond.
Covalent Bonds
Many nonmetal elements
exist as diatomic
molecules. Diatomic
means “two atoms.”
Multiple Covalent Bonds
When two atoms share three pairs of
electrons, the bond is called a triple bond.
When two atoms share two pairs of electrons,
the bond is called a double bond.
N N
Unequal Sharing of Electrons – Polar Covalent
Bonds
In a molecule of a compound, electrons may
not be shared unequally.
Except for noble gases, elements on the right
of the periodic table tend to have a greater
attraction for electrons than elements on the
left.
Elements at the top of a group tend to have a
greater attraction for electrons than elements
at the bottom of a group have.
A covalent bond in which electrons are not shared
equally is called a polar covalent bond.
Unequal Sharing of Electrons
Shared electrons in a hydrogen chloride
molecule spend less time near the hydrogen
atom than near the chlorine atom.
Unequal Sharing of Electrons
Polar and Nonpolar Molecules
Can you assume that a molecule that contains
a polar covalent bond is polar?
•
•
When a molecule has only two atoms, it will be
polar.
When molecules have more than two atoms, the
answer is not obvious.
Unequal Sharing of Electrons
In a carbon dioxide (CO2)
molecule, the polar bonds
between the carbon atom and
the oxygen atoms cancel out
because the molecule is linear.
In a water (H2O) molecule, the
polar bonds between the oxygen
atom and the hydrogen atoms
do not cancel out because the
molecule is bent.
Attraction Between Molecules
Dashed lines
represent attractions
between partially
positive hydrogen
atoms and partially
negative oxygen
atoms. The symbols
– and + are used to
indicate a partial
charge.
Assessment Questions
1.
What attractions hold two atoms in a molecule
together?
a.
b.
c.
d.
attraction between ions with opposite charges
attraction between the nuclei of the atoms and shared
electrons
attraction between each nucleus and the electrons of the
other atom
attraction between the molecule and other molecules
Assessment Questions
1.
What attractions hold two atoms in a molecule
together?
a.
b.
c.
d.
attraction between ions with opposite charges
attraction between the nuclei of the atoms and shared
electrons
attraction between each nucleus and the electrons of the
other atom
attraction between the molecule and other molecules
ANS: B
Assessment Questions
2. What determines whether a molecule is polar?
a. type of atoms and shape of molecule
b. mass of atoms and number of valence electrons
c. type and mass of atoms
d. ionization energy and number of covalent bonds
Assessment Questions
2. What determines whether a molecule is polar?
a. type of atoms and shape of molecule
b. mass of atoms and number of valence electrons
c. type and mass of atoms
d. ionization energy and number of covalent bonds
ANS: A
Assessment Questions
3. Why does water have a much higher boiling point
than methane?
a.
b.
c.
d.
Methane molecules are more polar, so its molecules
have stronger attractive forces.
Partial charges on the polar water molecules increase
attractive forces between molecules.
A water molecule has much more mass than a methane
molecule, so water has a higher boiling point.
Water has a higher boiling point because its molecules
do not contain carbon atoms.
Assessment Questions
3. Why does water have a much higher boiling point
than methane?
a.
b.
c.
d.
Methane molecules are more polar, so its molecules
have stronger attractive forces.
Partial charges on the polar water molecules increase
attractive forces between molecules.
A water molecule has much more mass than a methane
molecule, so water has a higher boiling point.
Water has a higher boiling point because its molecules
do not contain carbon atoms.
ANS: B