Transcript Adventures in Chemistry Julie T. Millard, Colby College

Chapter 5
Chemical Bonding and States of
Matter
Chapter Learning Objectives

By the end of the chapter, you will recognize
that
a. Having eight valence electrons is particularly
desirable (“the octet rule”).
b. Atoms form bonds with other atoms to satisfy
the octet rule.
c. The two major types of chemical bonds are ionic
and covalent.
Chapter Learning Objectives (cont)
d. Electronegativity is the ability to attract
shared electrons.
e. The type of bond formed between two
atoms depends on their difference in
electronegativity.
f. Ionic bonds form between atoms with a
large difference in electronegativity
(generally a metal and a nonmetal).
Chapter Learning Objectives (cont)
g. Nonpolar covalent bonds form between
atoms with little difference in electronegativity
(generally two nonmetals).
h. Polar covalent bonds form between atoms
with intermediate difference in
electronegativity.
i. Like dissolves like. That is, polar solutes
dissolve in polar solvents.
Chapter Learning Objectives (cont)
j. Intermolecular forces hold the molecules of a
material together in different states of matter.
k. Stronger intermolecular forces lead to higher
melting and boiling temperatures.
l. The relative strengths of intermolecular forces
generally follow the trend:
hydrogen bonds > dipole-dipole interactions > London forces
Chapter Outline
A. & B.



The Octet Rule
The noble gases of Group VIIIA do not
typically form compounds with other atoms.
Atoms with eight valence electrons are
particularly stable, an observation called the
octet rule.
Atoms form bonds with other atoms to
achieve a valence octet.
Octet Rule
An octet
is 8 valence electrons.
is associated with the stability of the noble gases.
He is stable with 2 valence electrons (duet).
He 2
valence electrons
2
Ne 2, 8
8
Ar
2, 8, 8
8
Kr
2, 8, 14, 8
8
Electronic
Configuration of Noble Gases
Chapter Outline
Types of compounds
C.
Ionic
1.

Attractions between oppositely charged
particles
Covalent
2.

Atoms share electron pairs.
Types of Compounds
Chapter Outline

Lewis Dot Structures (Review)


The number of valence electrons is equal to the
group number for most of the main group
elements.
In Lewis dot structures, the chemical symbol
represents the nucleus and the core electrons
and dots represent the valence electrons.
Lewis Dot Structures
Chapter Outline
Ionic Bonds
1.


Ionic compounds result from the loss of
electrons by one atom (usually a metal) and
the gain of electrons by another atom (usually
a nonmetal).
Ionic bonds arise from the attraction between
particles with opposite charges (electrostatic
forces); e.g., Na+ Cl-.
Ionic and Covalent Bonds
Atoms form octets
to become more stable.
by losing, gaining, or
sharing valence
electrons.
:
by forming ionic bonds or
covalent bonds.
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Metals Form Positive Ions known as Cations
Metals form positive ions (cations)
by a loss of their valence electrons.
with the electron configuration of the
nearest noble gas.
that have fewer electrons than
protons.
Group 1A metals 
Group 2A metals 
Group 3A metals 
ion 1+
ion 2+
ion 3+
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Formation of a Sodium Ion, Na+
Sodium achieves an octet by losing its one valence
electron.
2, 8, 1
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2, 8
Charge of Sodium Ion, Na+
With the loss of its valence electron,
the sodium ion has a +1 charge.
Sodium atom
11p+
11e0
Sodium ion
11p+
10e1+
2, 8
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Learning Check
A. The number of valence electrons in aluminum is
1) 1e-.
2) 2e-.
3) 3e-.
B. The change in electrons for octet requires a
1) loss of 3e-.
2) gain of 3e-.
3) a gain of 5e-.
C. The ionic charge of aluminum is
1) 3-.
2) 5-.
3) 3+.
D. The symbol for the aluminum ion is
1) Al3+.
2) Al3-.
3) Al+.
Solution
A. The number of valence electrons in aluminum is
3) 3 e-.
B. The change in electrons for octet requires a
1) loss of 3e-.
C. The ionic charge of aluminum is
3) 3+.
D. The symbol for the aluminum ion is
1) Al3+.
Formation of Negative Ions known as Anions
In ionic compounds, nonmetals
achieve an octet arrangement.
gain electrons.
form negatively charged ions with 3-, 2-, or 1charges.
Formation of a Chloride, ClChlorine achieves an octet by adding an electron to its
valence electrons.
2, 8, 7
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2, 8, 8
Charge of a Chloride Ion, Cl•
By gaining one electron, the chloride
ion has a -1 charge.
•
Chlorine atom
•
17p+
•
17e0
•
Chloride ion
17p+
18e1–
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Some Ionic Charges
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Learning Check
A. The number of valence electrons in sulfur is
1) 4e-.
2) 6e-.
3) 8e-.
B. The change in electrons for octet requires a
1) loss of 2e-.
2) gain of 2e-. 3) a gain of 4e-.
C. The ionic charge of sulfur is
1) 2+.
2) 2-.
3) 4-.
Solution
A. The number of valence electrons in sulfur is
2) 6e-.
B. The change in electrons for octet requires a
2) gain of 2e-.
C. The ionic charge of sulfur is
2) 2-.
The balance of charges in Al2O3
Run the following web animations/movies.
5.1: Formation of Sodium Chloride
5.2: Sodium Metal Reacting with Chlorine Gas
5.3: Ion Formation
Ionic Compounds
Naming Ionic Compounds with Two
Elements
•
To name a
compound that
contains two elements,
• identify the cation and
•
anion.
name the cation first
followed by the name of
the anion.
Charges of Representative Elements
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Names of Some Common Ions
•
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Learning Check
Complete the names of the following ions.
Ba2+
_________
Al3+
__________
K+
_________
N3
_________
O2
__________
F
_________
P3
_________
S2
__________
Cl
_________
Solution
Ba2+
barium
Al3+
aluminum
K+
potassium
N3
O2
F
nitride
oxide
fluoride
P3
S2
Cl
phosphide
sulfide
chloride
Examples of Ionic Compounds with
Two Elements
Formula
Name
NaCl
Ions
cation anion
Na+ Cl-
K2S
K+
S2-
potassium sulfide
MgO
Mg2+ O2-
magnesium oxide
CaI2
Ca2+ I-
calcium iodide
Al2O3
Al3+
aluminum oxide
O2-
sodium chloride
Learning Check
Write the names of the following compounds.
1) CaO
___________
2) KBr
___________
3) Al2O3
___________
4) MgCl2
___________
Solution
Write the names of the following compounds:
1) CaO
calcium oxide
2) KBr
potassium bromide
3) Al2O3
aluminum oxide
4) MgCl2
magnesium chloride
Polyatomic Ions
A polyatomic ion
• is a group of atoms.
• has an overall ionic charge.
Some examples of polyatomic ions are
NH4+
ammonium
OH−
hydroxide
NO3−
nitrate
NO2−
nitrite
CO32−
HCO3−
carbonate
PO43− phosphate
hydrogen carbonate
(bicarbonate)
Some Compounds with Polyatomic Ions

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Some Names of Polyatomic Ions
The names of common polyatomic anions
• end in ate.
NO3−
nitrate
PO43−
phosphate
• with one oxygen less end in ite.
NO2−
•
nitrite
PO33−
phosphite
with hydrogen attached use the prefix hydrogen (or bi).
HCO3−
hydrogen carbonate
(bicarbonate)
HSO3−
hydrogen sulfite
(bisulfite)
Names and Formulas of Common
Polyatomic Ions
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Publishing as Benjamin Cummings
Names and Formulas of Common
Polyatomic Ions

Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Naming Compounds with Polyatomic
Ions
• The positive ion is named first followed by the name of
the polyatomic ion.
NaNO3
sodium nitrate
K2SO4
potassium sulfate
Fe(HCO3)3
iron(III) bicarbonate
or iron(III) hydrogen carbonate
(NH4)3PO3
ammonium phosphite
Chapter Outline
Covalent Bonds
2.




Covalent bonds are formed when two atoms
share one or more electron pairs.
A molecule is the fundamental unit of a
covalent compound.
When two atoms share one pair of electrons,
the result is a single bond.
Two shared pairs of electrons is a double
bond; three is a triple bond.
Covalent Bonds
•
Covalent bonds form
•
when atoms share electrons to complete octets.
•
between two nonmetal atoms.
•
between nonmetal atoms from Groups 4A(14),
5A(15), 6A(16), and 7A(17).
Hydrogen Molecule
•
A hydrogen molecule
•
is stable with two electrons (helium).
•
has a shared pair of electrons.
Run the following web animations/movies.
5.4: Bond Length and Energy
5.5: Electrostatic Interactions Between Hydrogen Atoms
Forming Octets in Molecules

In a fluorine, F2,, molecule, each F atom
•
shares one electron.
•
attains an octet.
Carbon forms 4 covalent bonds
•
In a CH4, methane, molecule
•
a C atom shares 4 electrons to
attain an octet.
•
each H shares 1 electron to
become stable like helium.
Multiple Bonds
•
In nitrogen molecule, N2,
•
each N atom shares 3 electrons.
each N attains an octet.
the bond is a multiple bond called a triple bond.
the name is the same as the element.
•
•
•
Naming Covalent Compounds
•
•
To name covalent compoundsTable5.12
•
STEP 1: Name the first
nonmetal as an element.
•
STEP 2: Name the second
nonmetal with an ide ending.
•
STEP 3: Use prefixes to
indicate the number of atoms
(subscript) of each element.
•
Naming Covalent Compounds
•
What is the name of SO3?
•
1. The first nonmetal is S sulfur.
•
2. The second nonmetal is O named oxide.
•
3. The subscript 3 of O is shown as the prefix tri.
•
SO3  sulfur trioxide
•
•
•
The subscript 1 (for S) or mono is understood.
Naming Covalent Compounds
•
Name P4S3.
•
1. The first nonmetal P is phosphorus.
•
2. The second nonmetal S is sulfide.
•
3. The subscript 4 of P is shown as tetra.
•
The subscript 3 of S is shown as tri.
•
•
P4S3  tetraphosphorus trisulfide
Formulas and Names of Some Covalent
Compounds

Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Learning Check

Select the correct name for each compound.

A.SiCl4 1) silicon chloride
2) tetrasilicon chloride
3) silicon tetrachloride

B.
P2O5 1) phosphorus oxide
2) phosphorus pentoxide
3) diphosphorus pentoxide
C.
Cl2O7 1) dichlorine heptoxide
2) dichlorine oxide
3) chlorine heptoxide






Solution

Select the correct name for each compound.

A.SiCl4 3) silicon tetrachloride
B.
P2O5 3) diphosphorus pentoxide
C.
Cl2O7 1) dichlorine heptoxide


Covalent bonds are subclassified as
nonpolar or polar
Predicting Compounds using Lewis Dot
Structures

Going back to the idea of Lewis dot
configuration as a good way to keep track of
valence electrons for predicting structure of
ionic/covalent compounds.
Ionic Compounds

Magnesium Iodide using the crossover method to
determine the molecular formula and draw the
structure using Lewis dot valence electrons.
Step 1: Forming the magnesium cation:
Mg
Mg2+ + 2e-
Step 2: Forming the iodide anion:
I
+ 1e-
I
Step 3: Putting the ions together
We need 2 iodide anions to balance the +2
charge on the magnesium, as indicated by the
formula MgI2
I
Mg2+ I
Covalent Compounds

Covalent compounds between oxygen and
hydrogen
Step 1: Determine how many bonds are formed by oxygen
Step 2: Determine how many hydrogen atoms are in the
chemical formula (hydrogen forms a single bond)
Step 3: Draw the structure
Draw the structure for H2O
6 valence e-
O
2 max bonds
1 valence e-
H
1 bond each
and
2
H
6 valence e- 1 valence e-
H
O
O
H2O
H
Covalent Compounds

Covalent compounds between carbon and hydrogen
Step 1: Determine how many bonds are formed by carbon
Step 2: Determine how many hydrogen atoms are in the
chemical formula (hydrogen forms a single bond)
Step 3: Draw the structure
Draw the structure for CH4
4 valence e-
C
4 max bonds
1 valence e-
H
1 bond each
H
and
4
H
H
C
C
H
H
CH4
4 valence e- 1 valence e-
Chapter Outline
Equal Sharing versus Unequal Sharing
d.



When two different kinds of atoms are bonded,
the electrons are usually shared unequally.
When a bond exists between two identical kinds
of atoms, the electrons are shared equally.
An atom with greater electronegativity has a
greater ability to attract shared electrons.
Electronegativity
Chapter Outline
Equal Sharing versus Unequal Sharing
(cont)
d.

The greater the difference in electronegativity
between two atoms that are covalently bonded,
the more polar is the bond.
Polar vs. Nonpolar Bonds
Paired molecules much different in
electronegativity play tug of war
Credit: Courtesy of Julie Millard
Chapter Outline
States of Matter
j.
Review of Types of Bonds

1.
2.
3.
Chemical bonds (intramolecular forces) hold atoms
together.
The three types of chemical bonds are ionic, polar
covalent, and nonpolar covalent.
Intermolecular forces hold molecules together.
Types of Bonds
Chapter Outline
States of Matter (cont)
j.
Particle Cohesion Determines Physical State

1.
In general, the relative strengths of intermolecular
forces follows the trend:
gases < liquids < solids
Changes of State



Adding energy breaks intermolecular forces and
causes molecules to change their state.
The stronger the intermolecular forces of a compound,
the higher are the melting and boiling points.
Changes of State
Chapter Outline
Types of Intermolecular Forces within
Pure Substances
k.
London dispersion forces




A temporary dipole in one molecule can induce a
dipole in a neighboring molecule.
The negative end of one temporary dipole can
attract the positive end of an induced dipole; these
attractions are called London dispersion forces.
London forces tend to be fairly weak.
Instantaneous dipoles from electron
movements
London Dispersion Forces
Chapter Outline

Types of Intermolecular Forces within Pure
Substances (cont)

Dipole-dipole interactions


Dipole-dipole interactions exist between molecules with
polar covalent bonds.
Dipole-dipole interactions are typically stronger than
London dispersion forces.
Dipole-Dipole Interactions
Chapter Outline

Types of Intermolecular Forces within
Pure Substances (cont)

Hydrogen Bonds



Hydrogen bonds are a special type of dipole-dipole
interaction.
Hydrogen bonds can occur when H is bonded to
one of the highly electronegative atoms N, O, or F.
An example is H2O.
Hydrogen bonds are typically quite strong.
Hydrogen Bonds in Water
Ice crystal lattice
Run the following web animations/movies.
5.6: Electric Current Conduction by Molten Salts
5.8a: Atomic Motion and Thermal Energy
5.9: Atomic Properties of Solids, Liquids, and Gases
Chapter Outline
Forming Solutions
i.
Like dissolves like




Ionic solutes often dissolve in polar solvents;
e.g., NaCl dissolves in H2O.
Polar solutes generally dissolve in polar
solvents; e.g., NH3 in H2O.
Nonpolar solutes generally do not dissolve well
in polar solvents; e.g., oil in H2O.
Run the following web animations/movies.
5.10: Like Dissolves Like Solubility
NaCl Dissolving in H2O
Polar covalent molecules with dipoles can
induce dipoles in nonpolar molecules
Why octane molecules and water
don't mix
Oil and water do not mix
Credit: Visuals Unlimited
Chapter Outline

Emulsions


Emulsifying agents are molecules that contain a
polar portion and a nonpolar region.
Soap is an example of an emulsifying agent that
can form a suspension of a nonpolar material in a
polar solvent (an “emulsion”).
Emulsification with Soap
Chapter Outline
Measuring Amounts in Solution
l.
Solubility


The maximum amount of a solute that dissolves in a
solvent
Molarity



The amount of a solute dissolved in a solvent is its
concentration.
Concentration is often measured in moles/liter, also
called molarity (M).
Parts per million (ppm)


The concentration of a dilute solution may be measured
in parts per million (grams of solute per million grams
solution).
Solubilities of various Ionic
Compounds in Water
Key Words











Chemical bonds
Noble gases
Octet rule
Ionic compound
Ion
Covalent compound
Lewis dot structures
Core electrons
Cation
Anion
Electrostatic forces











Chemical formula
Lone pair
Single bond
Double bond
Triple bond
Isomers
Nonpolar covalent bond
Polar covalent bond
Electronegativity
Dipole
Structure
Key Words








Intermolecular forces
London dispersion forces
Dipole-dipole interactions
Hydrogen bonds
Solution
Solute
Solvent
Aqueous solution








Colloid
Suspension
Amphiphilic/
amphipathic
Emulsion
Solubility
Concentration
Molarity (M)
Parts per million (ppm)