Ch. 7 - Chemical Bonds
- Chemistry
I. Why Atoms Combine
A. Chemical Formula
• Shows:
1) The number of elements in the compound
2) The number of their atoms
H2O
1 oxygen atom
2 hydrogen atoms
B. Chemical Bond
• Strong attractive force between atoms or ions in a
molecule or compound.
• Formed by:
– transferring e- (losing or gaining)
– sharing e-
C. Stability
• Octet Rule
N
e
– most atoms form bonds in order to have 8 valence e– full outer energy level
– like the Noble Gases!
A full outer shell will have:
2 electrons in the s subshell and
6 electrons in the p subshell ( s2p6 configuration)
 Stability is the driving force behind
bond formation!
Reactions
• Atoms can react with one another to form new
substances called compounds.
• Compounds are formed when two or more
atoms chemically bond together
• The resulting compound is unique both
chemically and physically from its parent atoms.
Example!
• Magnesium + Oxygen
Magnesium Oxide
Chemical Bonds
There are three basic types of bonds:
Ionic - The electrostatic attraction between ions
Covalent - The sharing of electrons between atoms
Metallic - Each metal atom bonds to other metals
atoms within a "sea" of electrons (covered in a later unit)
Ionic Compounds
and
Ionic Bonding
The Periodic Table of the Elements (review)
The periodic table can be also divided into metals (left/blue) and nonmetals
(right/yellow).
A few elements retain some of the properties of metals and nonmetals, they are called
metalloids (staircase/pink).
B
Si
Ge
As
Sb Te
?
3
Which pair of elements would you expect to exhibit the greatest
similarity in their physical and chemical properties?
A
H, Li
B
Cs, Ba
C
Ca, Si
D
Ga, Ge
E
C, O
F
I don't know how to answer this.
4
Which one of the following is a nonmetal?
A
W
B
Sr
C
Os
D
Ir
E
S
F
I don't know how to answer this.
5
Potassium is a __________ and chlorine is a __________.
A
metal, nonmetal
B
metal, metal
C
metal, metalloid
D
metalloid, nonmetal
E
nonmetal, metal
F
I don't know how to answer this.
Valence Electrons
Valence electrons are the electrons in the highest occupied
energy level of an element’s atoms.
The number of valence electrons largely determines the
chemical properties of an element.
Valence
electron
To find the number of valence electrons in an atom of a representative element,
simply look at its group number.
Atoms in group 3 have 3 valence electrons,
atoms in group 17 have 7 valence electrons, etc.
Common Ion Charges
1+
0
2+
3+ NA 3- 2- 1-
6
How many valence electrons does Aluminum have?
A
5
B
7
C
3
D
27
E
I don't know how to answer this.
7
How many valence electrons does Barium have?
A
1
B
2
C
52
D
3
E
I don't know how to answer this.
Ions
Cations are positive and are formed by
elements on the left side of the
periodic chart (metals).
Anions are negative and are formed
by elements on the right side of the
periodic chart (nonmetals).
The Formation of Cations
Metals usually give up valence electrons
This results in a noble gas (8 electron) outer shell.
Na : 1s2 2s2 2p6 3s1
Na+1 : 1s2 2s2 2p6
Ne atom
Loss of valence
electrons
The configuration of the Sodium ion is the same as Neon
Metal gets smaller when it becomes a cation
The Formation of Cations
Cations of Group 1A elements always have a charge
of 1+.
Cations of Group 2A elements always have a charge
of 2+.
Mg
Magnesium atom
(electrically
neutral,
charge = 0)
Mg2+
Magnesium ion
(+2 indicates 2 units of
positive charge)
+
2e-
(2 in front of e- indicates 2
units of negative charge)
The Formation of Anions
Nonmetals usually gain valence electrons.
This results in a noble gas (8 electrons) outer shell
Cl: 1s2 2s2 2p6 3s2 3p5
Cl- 1s2, 2s2, 2p6, 3s2, 3p6
A chloride ion has the same electron configuration as argon.
Ar atom
Non metal gets bigger when it becomes a cation
The Formation of Anions
Anions of Group 15 (5A) elements have a
charge of 3-
Anions of Group 16 (6A) elements always have
a charge of 2-
Anions of Group 17 (7A) elements have a
charge of 1-
8
Metals tend to __________ electrons and cations tend to
__________ electrons.
A
gain, gain
B
lose, lose
C
gain, lose
D
lose, gain
E
neither, they keep their electrons
F
I don't know how to answer this.
Anions tend to be __________ and cations tend to be __________.
9
A
metals, metals
B
nonmetals, nonmetals
C
metals, nonmetals
D
nonmetals, metals
E
metalloids, metalloids
F
I don't know how to answer this.
10
Metals lose electrons to form cations
True
False
11
Anions are formed from nonmetals
True
False
12
Nonmetals tend to lose electrons forming ions
True
False
13
This is the ion formed from a calcium atom
A
Ca+
B
Ca2+
C
Ca-
D
Ca2-
E
I don't know how to answer this.
14
Barium forms an ion with a charge of __________.
A
1+
B
2-
C
3+
D
3-
E
2+
F
I don't know how to answer this.
15
Aluminum forms an ion with a charge of __________.
A
2+
B
1-
C
3+
D
2-
E
0
F
I don't know how to answer this.
16
Of the following, __________ contains the greatest number of
electrons.
A
P3+
B
P
C
P2-
D
P3-
E
P2+
F
I don't know how to answer this.
17
Oxygen forms an ion with a charge of __________.
A
2-
B
2+
C
3-
D
3+
E
6+
F
I don't know how to answer this.
18
Iodine forms an ion with a charge of __________.
A
7-
B
1+
C
2-
D
2+
E
1-
F
I don't know how to answer this.
19
This is the ion formed from nitrogen
A
N-
B
N2-
C
N3+
D
N3-
E
I don't know how to answer this.
20
Predict the charge of the most stable ion of S?
A
3+
B
1-
C
6+
D
2+
E
2-
F
I don't know how to answer this.
Ionic Bonding
Electronegativity is how strongly an atom attracts electrons.
Atoms with a high electronegativity will be able to attract electrons away from atoms
with a much lower electronegativity.
This removal of electrons can occur when the difference in electronegativity between
the two atoms is approximately 1.7 or higher.
Once a positive and negative ion are formed, they will be attracted to each other via
the electrostatic force:
F = k q1 q2
r2
Note: The heavier nonmetals from 4,6,5th
groups
( In, Tl, Sn, Pb, Sb Bi )
may act like metals
Ionic Bonding
An electronegativity difference of approximately 1.7 can
only occur between a metal and a nonmetal.
Which pair of atoms will form an ionic bond?
21
A
Li and Ne
B
K and Br
C
K and Cs
D
S and Cl
E
I don't know how to
answer this.
Which pair of atoms will form an ionic bond?
22
A
Li and Be
B
Na and Mg
C
K and Ca
D
Na and Cl
E
I don't know how to
answer this.
23
Which of the following compounds would you expect to be ionic?
A
H2O
B
CO2
C
SrCl2
D
SO2
E
H2S
F
I don't know how to answer this.
Formation of Ionic Compounds
Compounds composed of cations and anions are
called ionic compounds.
Although they are composed of ions, ionic
compounds are electrically neutral.
The electrostatic forces that hold ions together
in ionic compounds are called ionic bonds.
Ionic Bonds
The electron transfer process in creating an ionic bond:
Na
Cl
The dots represents the valence electrons in an atom.
click here for an animation of this
reaction
Formula Units
A chemical formula shows the kinds and
numbers of atoms in the smallest
representative unit of a substance.
A formula unit is the lowest whole-number
ratio of ions in an ionic compound.
Every ionic compound has a 3D array of
positive and negative ions.
[*]
Properties of Ionic Compounds
They are crystalline solids at room temperature
They have high melting points
They conduct electricity when melted (molten) or dissolved in water
(aqueous)
Predicting an Ionic Compound Formula
Potassium (K) with an electronegativity of 0.8 and oxygen (O) with an electronegativity of
3.5 will form an ionic compound.
What is the formula for an ionic compound
of potassium and oxygen?
How many additional valence electrons does oxygen want?
How many valence electrons does potassium have?
How many potassium atoms will it take to give oxygen the
electrons it needs?
The formula unit is K2O
Always Metal First (low electonegativity)
Alternate Method
If you don't like finding least common multipliers, you can use this alternative
method:
1. Write down the ions side by side along with their charge. Always write the
metal first.
2. "Criss-cross" the numerical values of the charges.
3. Reduce subscripts to lowest ratio.
Mg
N
Mg
N
Mg
24
The formula for the ionic between Cs and O is:
A
CsO2
B
OCs2
C
Cs2O
D
OCs2
E
I don't know how to do this.
25
The ionic compound between Ca and N is:
A
CaN
B
Ca2N2
C
Ca3N2
D
Ca2N3
E
I don't know how to do this.
26
The ionic compound between Al and O
A
Al3O2
B
Al2O3
C
D
AlO
E
Al2O2
I don't know how to do this.
27
What is the ionic compound formed between Ca and Al?
A
CaAl
B
Ca3Al2
C
Al2Ca3
D
No compound is formed.
E
I don't know how to do this.
28
What is the ionic compound formed between P and Br?
A
P3Br
B
BrP
C
no ionic compound
D
(BrP)2
E
I don't know how to do this.
29
What is the formula for sodium phosphide?
A
SP3
B
NaP
C
Na3P
D NaP3
E
I don't know how to do this.
30
What is the formula for strontium bromide?
A
SrBr
B
SrBr2
C
Sr2Br
D BrSr2
E
I don't know how to do this.
31
The formula for barium sulfide is Ba2S2.
True
False
Naming Binary Ionic Compounds - Cations
Many cations have the same name as the original, neutral atom.
Charge
formula
name
______________________________
1+
H+
Hydrogen ion
Li +
Lithium ion
K+
Potassium ion
Cs +
Cesium ion
Ag +
Silver ion
2+
Mg 2+
Ca 2+
Ba 2+
Zn 2+
Cd 2+
Magnesium ion
Calcium ion
Barium ion
Zinc ion
Cadmium ion
3+
Al 3+
Aluminum ion
Naming Binary Ionic Compounds
Binary (two-element) compounds are named by
writing the name of the cation followed by the name
of the anion.
The name of the cation is the same as the metal
name.
The name of the anion is the name of the non-metal
with
the suffix changed to -ide.
Binary compounds end in "-ide."
Examples:
NaCl = sodium chloride
KI = potassium iodide
Li2S = lithium sulfide
32
Na2S is
A
Sodium sulfate
B
Sodium sulfide
C
Di-sodium sulfide
D
Sulfur nitride
E
I don't know how to do this.
The correct name for SrO is __________.
33
A
strontium oxide
B
strontium hydroxide
C
strontium peroxide
D
E
strontium monoxide
F
I don't know how to do this.
strontium dioxide
The correct name for Al2O3 is __________.
34
A
aluminum trioxide
B
dialuminum oxide
C
dialuminum trioxide
D
aluminum oxide
E
aluminum hydroxide
F
I don't know how to do this.
Cations formed by Transition Elements
Recall that s-block metals have only one
possible ionic charge, based on the Octet
Rule.
However, most transition metals can have more
than one ionic charge. For this reason, there
is a system for designating each ion.
Sn, Pb from the p block will form more than
one type of ions and behave like transition
metals.
Cations Formed by Transition Elements
Only common transition metals
are shown.
Silver, cadmium and zinc only form one cation, Ag+, Cd2+ and Zn2+
Note the mercury cations.
Tin and Lead act like transition metals.
Writing Formulas with Transition Metals
Example: Copper (II) Chloride
Step 1:
write out name with space
Step 2:
Cu
2+
Cl
1-
write symbols & charge of elements
Step 3:
cu1
Cl
criss-cross charges as subsrcipts
Step 4:
combine as formula unit
(“1” is never shown)
CuCl
2
2
Criss-Cross Rule
Example: Copper Chloride
Step 1:
Aluminum
Chloride
Step 2:
+1
Cu
1Cl
Step 3:
Cu
Cl
Step 4:
CuCl
35
Which metal is capable of forming more than one cation?
A
K
B
Cs
C
Ba
D
Al
E
Sn
F
I don't know how to answer this.
Formulas with Transition Metals
In order to correctly name a formula containing a transition
metal, it is necessary to first determine the charge on the
cation.
Since all compounds are neutral, then the total positive cation
charge must equal the total negative anion charge.
In other words:
Total cation charge + Total anion charge = 0
(charge of cation) (# of cations) + (charge of anion) (# of anions)
=0
Example Formula with Transition Metals
In the case of FeCl3, we make the following substitutions:
(charge of cation) (# of cations) +(charge of anion) (# of anions) =
0
(x) (1) + (-1) (3) = 0
Thus x = 3 and the cation is Fe3+ or iron(III).
37
The name of FeCl3 is
A
iron chloride
B
iron (II) chloride
C
iron (III) chloride
D
I don't know how to answer this.
[*]
38
The formula for tin (IV) oxide is
A
SnO
B
Sn2O
C
SnO2
D
SnO
E
I don't know how to answer this.
39
The formula for copper (II) sulfide is
A
CuS2
B
CuS
C
Cu2 S2
D
(CuS)2
E
I don't know how to answer this.
41
The charge on the cation in the salt Fe2O3 is __________.
A
1+
B
2+
C
3+
D
5-
E
6-
F
I don't know how to answer this.
[*]
42
What is the charge on zirconium ion in ZrO2 ?
A
2+
B
4+
C
1+
D
2-
E
I don't know how to answer this.
Polyatomic Compounds
NaNO2
sodium nitrite
KClO3
potassium chlorate
Ca3(PO4)2
calcium phosphate
Fe(OH)3
iron (III) hydroxide
NaHCO3
sodium bicarbonate
‘sodium hydrogen carbonate’
Common Polyatomic Ions
Names of Common Polyatomic Ions
Ion
NH4 1+
NO2 1NO3 1widely
SO3 2SO4 2HSO4 1OH 1CN 1PO4 3HPO4 2H2PO4 1-
Name
ammonium
nitrite
nitrate
sulfite
sulfate
hydrogen sulfate
(“bisulfate” is a widely
used common name)
hydroxide
cyanide
phosphate
hydrogen phosphate
dihydrogen phosphate
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 100
Ion
CO3 2-
ClO 1ClO2 1ClO3 1ClO4 1C2H3O2 2MnO4 1Cr2O7 2CrO4 2O2 2-
Name
carbonate
HCO3 1hydrogen carbonate
(“bicarbonate” is a
used common name)
hypochlorite
chlorite
chlorate
perchlorate
acetate
permanganate
dichromate
chromate
peroxide
Polyatomic Ions (con't)
Most of the polyatomic ions contain oxygen
atoms.
Many anions names end with “-ite” or “-ate”
In “ite/ate” pairs, the ion with fewer oxygen
atoms
will have the “ite” ending
Examples: sulfite /sulfate
nitrite /nitrate
Note that the suffix does not indicate the actual
number of O atoms.
Super Criss-Cross Rule
or
Writing polyatomic ionic
compounds
Magnesium Phosphate
Step 1:
Magnesium
Step 2:
2+
Mg
Step 3:
Mg
Step 4:
3
Phosphate
3PO4
(PO4)
Mg3(PO4)2
2
polyatomic Compounds
Ca3(PO4) 2
1. ________________
calcium phosphate
(NH4)2CO3
2. ________________
ammonium carbonate
3. ________________
Al2(SO4)3
aluminum sulfate
4.
Na2SO4
____________________
sodium sulfate
5.
LiCN
____________________
lithium cyanide
6.
Ba(ClO3)2
7. ________________
Cu(OH)2
____________________
barium chlorate
copper (II) hydroxide
polyatomic Compounds
Ca3(PO4) 2
1. ________________
calcium phosphate
(NH4)2CO3
2. ________________
ammonium carbonate
3. ________________
Al2(SO4)3
aluminum sulfate
4.
Na2SO4
____________________
sodium sulfate
5.
LiCN
____________________
lithium cyanide
6.
Ba(ClO3)2
7. ________________
Cu(OH)2
____________________
barium chlorate
copper (II) hydroxide
Common Polyatomic Ions
Names of Common Polyatomic Ions
Ion
NH4 1+
NO2 1NO3 1widely
SO3 2SO4 2HSO4 1OH 1CN 1PO4 3HPO4 2H2PO4 1-
Name
ammonium
nitrite
nitrate
sulfite
sulfate
hydrogen sulfate
(“bisulfate” is a widely
used common name)
hydroxide
cyanide
phosphate
hydrogen phosphate
dihydrogen phosphate
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 100
Ion
CO3 2-
ClO 1ClO2 1ClO3 1ClO4 1C2H3O2 2MnO4 1Cr2O7 2CrO4 2O2 2-
Name
carbonate
HCO3 1hydrogen carbonate
(“bicarbonate” is a
used common name)
hypochlorite
chlorite
chlorate
perchlorate
acetate
permanganate
dichromate
chromate
peroxide
43
The formula for sodium hydroxide is
A
Na (OH)2
B
Na(OH)
C
Na(OH2)
D
Na(HO)
E
I don't know how to answer this.
44
The formula for aluminum phosphate is:
A
Al(PO4 )
B
Al3(PO4)
C
Al2(PO4)3
D
Al3(PO4)3
E
I don't know how to answer this.
45
The formula for magnesium carbonate is :
A
Mg2(CO3)
B
Mg(CO3)
C
Mg2(CO3)2
D
Mg(CO3)2
E
I don't know how to answer this.
46
The formula for calcium sulfate is
A
B
Ca(SO4)
Ca2(SO4)2
C
Ca(SO3)
D
Ca2(SO3)2
E
I don't know how to answer this.
47
NaClO is
A
sodium chlorate
B
sodium chloride
C
D
sodium chlorite
E
sodium hypochlorite
I don't know how to answer this.
48
Mg(HCO3)2 is
A
Magnesium carbonate
B
Magnesium hydrogen carbonate
C
Magnesium hydroxide
D
Magnesium carboxide
E
I don't know how to answer this.
49
Ammonium carbonate is
A
(NH4)(CO3)
B
(NH4)2(CO3)
C
(NH4)(CO3)2
D
E
(NH4)2(CO2)
I don't know how to answer this.
PRACTICE
Writing Formulas for Ionic Compounds
Complete the table by filling in the formula for the ionic compound formed by each pair of
cations and anions, as shown for the first pair.
PRACTICE
Writing Formulas for Ionic Compounds
Write the formula for the following compounds:
1. Magnesium iodide
2. Calcium sulfite
3. Barium hydrogen carbonate
4. Iron (III) phosphate