Ch. 4: Compounds
and Their Bonds
Chem. 20
El Camino College
1
Octet Rule
8 e-s is a magic number
 Main Group elements (except H and He)
will give, take, or borrow electrons to reach
8 electrons in the outermost shell
 Noble Gases (except He) have 8 electrons
in the outer shell, so they don’t give or take
electrons

3
Cations: Positive Ions
Atoms are neutral
 Ions have a charge
 Cations are positive, Anions are negative
 Metals lose e-s easily to form cations
 When electrons are lost, the particle left
over has a positive charge.

4
Main Group. Cations:
Positive Ions
Ex. Sodium atom has one valence electron.
When Na loses 1 e-, a cation with a positive
charge forms
 The name of Na+ is sodium ion
 Note, for a +1 charge, just show +.

5
Main Group. Cations:
Positive Ions
Ex. Mg atom has 2 valence electrons
 When Mg loses 2 electrons, a cation with a
+2 charge forms
 The name of Mg2+ is magnesium ion
 Note, show the number, then the charge.

6
7
8
Anions: Negative Ions
Nonmetals gain electrons easily to form
anions
 When electrons are gained, the particle has
a negative charge
 Example: When Cl gains 1 e-, an anion with
-1 charge forms
 The name of Cl- is chloride ion.

9
10
Anions: Negative Ions
Ex. How many valence e-s does N have?
5
 How many e-s will N gain to reach 8?
3
 The formula for nitride ion is N3
11
Names of Ions
For metal ions in groups. 1, 2, and 3, the
name is the metal plus the word “ion”
 K+ is potassium ion
 Ca2+ is calcium ion
 What is the name of Al3+?
 aluminum ion

12
Names of anions
For anions (nonmetal ions), the name is the
nonmetal in ide form, plus the word “ion”
 F- is fluoride ion
 O2- is oxide ion
 What is the name of S2-?
 sulfide ion

13
Name These
Li
 Li+
 P3P
 Ba2+
 Ba

lithium
 lithium ion
 phosphide ion
 phosphorus
 barium ion
 barium

14
Charges from Group number
Gp 1 (1A) metals form + ions
 Gp 2 (2A) metals form 2+ ions
 Gp 13 (3A) metals form 3+ ions

Gp 15 (5A) nonmetals form 3- ions
 Gp 16 (6A) nonmetals form 2- ions
 Gp 17 (7A) nonmetals form - ions

15
16
Ionic Compounds
An ionic bond occurs when one atom gives
electrons to another
 Compounds always have zero charge.

17
18
19
Predicting Ionic Formulas
Determine the charge of each ion
 Combine ions to get zero charge overall
 Use the lowest numbers possible
 Ex. A compound contains sodium ions and
sulfide ions. Write the formula.
 Sodium ion is Na+, sulfide ion is S2 It will take 2 Na+ ions to cancel the charge
in one S2- ion
 The formula is Na2S.

20
21
Write the Formulas
compound contains
 potassium ions, iodide ions
 chloride ions, calcium ions
 aluminum ions, nitride ions
 beryllium ions, fluoride ions
 sulfide ions, lithium ions
 aluminum ions, oxide ions
KI
 CaCl2
 AlN
 BeF2
 Li2S
 Al2O3

22
Naming Ionic Compounds
The 1st word is the cation name (metal ion)
 The 2nd word is the anion name
 Never use the word “ion” in a name
 lithium bromide
 LiBr
 magnesium fluoride
 MgF2
 calcium sulfide
 CaS
 calcium phosphide
 Ca3P2
 potassium oxide
 K 2O
 aluminum chloride
 AlCl3

23
24
Transition Metal Ions
Some transition metals may form many cations
 Know these transition metal ions

Cr2+, Cr3+
 Fe2+, Fe3+
 Cu+, Cu2+
 Sn2+, Sn4+
 Pb2+, Pb4+

chromium(II) ion, chromium(III) ion
iron(II) ion, iron(III) ion
copper(I) ion, copper(II) ion
tin(II) ion, tin(IV) ion
lead(II) ion, lead(IV) ion
27
Transition Metal Ions









Chromium can form two ions: Cr2+, Cr3+
To name, use a Roman numeral in parentheses and the
word “ion”
The name of Cr3+ is chromium(III) ion
What is the name of Pb4+?
lead(IV) ion (note--parentheses are only for elements
that form more than one ion such as Cr, Fe, Cu, Sn, Pb)
What is the name of Ag?
silver
What is the name of Ag+?
silver ion
28
30
Transition Metals in
Compounds







When a compound contains a transition metal with
variable charge, you must determine what the charge is
Ex. Name FeCl2
Is that Fe2+ or Fe3+?
Since chloride ion is Cl- and there are 2 of them, this
must be iron(II) ion
Iron(II) chloride
Write the formula for iron(III) bromide
FeBr3
31
Examples








Name CuO, Cu2O, Fe2S3, FeO, PbS, PbS2, AgCl
copper(II) oxide
copper(I) oxide
iron(III) sulfide
iron(II) oxide
lead(II) sulfide
lead(IV) sulfide
silver chloride
32
Formulas







Jumbo Practice 1
chromium(III) bromide, chromium(II) sulfide, zinc oxide,
tin(II) nitride, tin(IV) nitride, tin(II) oxide
CrBr3
CrS
ZnO
Sn3N2
Sn3N4
SnO
33
Polyatomic Ions



Polyatomic ions are ions that contain more than 1 atom
Never change the numbers inside or the charge of a
polyatomic ion
If you need more than one polyatomic ion, use
parentheses.
34
35
OH




Hydroxide ion is OHTo write the formula of sodium hydroxide
Sodium ion is Na+
Hydroxide ion is OHNaOH
36
OH




To write the formula of calcium hydroxide
Calcium ion is Ca2+
Hydroxide ion is OHCa(OH)2
Note: Writing CaO2H2 or CaOH2 is incorrect
37
Other Polyatomic Ions


Nitrate ion NO3-, sulfate ion SO42-, phosphate ion PO43Write the formulas for sodium nitrate, sodium sulfate, and
sodium phosphate




NaNO3
Na2SO4
Na3PO4
Write the formulas for calcium nitrate, calcium sulfate,
and calcium phosphate



Ca(NO3)2
CaSO4
Ca3(PO4)2
39
Other Polyatomic Ions







Be careful with similar sounding ions
sulfate ion SO42-, sulfite ion SO32-, sulfide ion S2hydrogen sulfate ion HSO4carbonate ion CO32hydrogen carbonate ion HCO3acetate ion C2H3O2ammonium ion NH4+
40
41
Examples






Name CuNO3, Cu2SO3, ZnSO3, Sn(C2H3O2)4, KHCO3
copper(I) nitrate
copper(I) sulfite
zinc sulfite
tin(IV) acetate
potassium hydrogen carbonate
42
Formulas






chromium(III) hydrogen sulfate, iron(II) phosphate,
zinc hydroxide, tin(II) carbonate, ammonium acetate
Cr(HSO4)3
Fe3(PO4)2
Zn(OH)2
SnCO3
NH4C2H3O2
43
Ionic vs. Covalent
All the compounds we’ve looked at so far
are ionic
 The cation of an ionic compound is a metal
ion or ammonium ion
 The anion of an ionic compound is a
nonmetal ion or polyatomic ion
 In ionic compounds, e s are given from one
atom to another.

44
Ionic vs. Covalent
Covalent compounds are made of 2
nonmetals
 In covalent compounds, e s are shared (not
given away)
 Covalent compounds are called molecules
 Ionic compounds are never called
molecules.

45
46
Diatomic Molecules are Formed
by Covalent Bonds
•There are 7 elements that form diatomic
molecules
•Formulas for these elements are always
shown with subscript “2”
F2 fluorine
H2 hydrogen
Cl2 chlorine
N2 nitrogen
Br2 bromine
O2 oxygen
I2 iodine
47
48
Fig. 6-1, p. 137
49
50
Examples
•
Write the formulas
•
•
•
•
•
•
gold
iodine
helium
nitrogen
oxygen
potassium
Au
I2
He
N2
O2
K
51
Naming Compounds
•
•
•
A compound is 2 or more elements bonded
together
The rules for naming covalent (nonmetalnonmetal) compounds are different than the
rules for ionic (metal-nonmetal) compounds
Always check the periodic table to decide
which rules to use.
52
Molecular Compounds
(Nonmetal-Nonmetal)
•
•
•
•
We’ll only be naming binary molecular (nonmetalnonmetal) compounds (made of 2 elements)
The 1st word is the name of the 1st element
The 2nd word is the name of the 2nd element in
“ide” form
Use a prefix for the number.
53
Prefixes in Molecular
Compounds
•
•
•
•
•
One: monoTwo: diThree: triFour: tetraFive: penta-
•
•
•
•
•
Six: hexaSeven: heptaEight: octaNine: nonaTen: deca-
54
Putting it all Together
•
•
•
•
CO2 is a molecular compound
The 1st word is the name of the 1st
element: carbon (the prefix mono is omitted
in the 1st word)
The 2nd word is the 2nd element in “ide”
form, with the prefix “di”
The name is carbon dioxide.
55
56
Examples
•
Name these: NF3, S2Br4, CCl4, N2
•
nitrogen trifluoride
•
disulfur tetrabromide
carbon tetrachloride
nitrogen
•
•
57
Awkward Vowel
Combinations
•
•
•
When the combinations “ao” or “oo”
appear, remove the first awkward vowel
Example: SiO4 is silicon tetroxide
Name P2O5, I2O, and SI2
•
•
•
diphosphorus pentoxide
diiodine monoxide
sulfur diiodide
58
Water and Ammonia


The name of H2O is water
The name of NH3 is ammonia.
59
60
Sharing electrons between
Different Nonmetals
Most nonmetals share electrons to reach 8
electrons
 Except: H reaches 2e s, B reaches 6 e s
 e dot formulas show how e s are shared

61
62
63
e- Dot Formulas
Electrons in covalent compounds exist as
bonding pairs or as lone pairs
 A bonding pair is 2 elctrons shared
between 2 atoms
 A lone pair is a pair of electrons around the
outside of an atom

64
65
e- Dot Formulas
Use this guide to help you connect the dots
 H gets 1 bond
 B gets 3 bonds
 C, Si get 4 bonds
 N, P get 3 bonds and 1 lone pair
 O, S get 2 bonds and 2 lone pairs
 F, Cl, Br, I get 1 bond and 3 lone pairs

66
67
e- Dot Formulas
:
C
N
O
: :
B
:
:
H
X:
:
P
:
:
Si
S
68
e- Dot Formulas
X represents any halogen. Halogens get 1
bond and 3 lone pairs.
 Halogens never get 2 bonds.

69
Examples
Draw these molecules. Be careful about how
many bonds and lone pairs each atom
prefers to have.
BI3
SCl2
CH4
:
:I:
:
:
I
:
:
:
: Cl
S
: :
:I
: :
:
:
B
H
Cl :
C
H
H
H
70
Examples
Draw these molecules. Be careful about how
many bonds and lone pairs each atom
prefers to have.
BH3
H 2O
PCl3
:
:
:
H
:
H
Cl :
: Cl
: Cl :
:
H
:
B
H
:
H
P
:
O
71
Double and Triple Bonds are
also possible
Draw CO2 (C is in the center)
:
C
O
:
: :
O
:
:
Draw CH2O (all atoms attached to C)
O
C
H
Draw N2
:N
N:
H
72
73
74
VSEPR: Valence Shell
Electron Pair Repulsion Theory
VSEPR Theory predicts the shapes of
molecules
 e sets (bonds or lone pairs) get as far
away from each other as possible
 Geometry is determined around one atom
at a time.

75
VSEPR

One “set” is a lone pair or a single bond or a
double bond or a triple bond
A single, double, or triple bond connects to a
bonded atom (BA).
A lone pair (LP) is not bonded to anything

Molecular shapes use bonded atoms (BA) only.


76
Ex: How many sets are around each indicated atom?
How many bonded atoms and how many lone pairs?
:
:
cO
H
C
H
H
b
d
N
H
Sets
4
3
3
4
4
2
2
4
H
C
e
f
C
g
C
BA
4
3
1
3
4
2
2
2
H
O
:
:
a.
b.
c.
d.
e.
f.
g.
h.
C
:
a
H
h
LP
0
0
2
1
0
0
0
2 77
78
Fig. 12-1, p. 325
Atoms with 2 Sets

When an atom has 2 sets around it, e- repulsion
pushes the sets as far apart as possible from
each other
The two sets will be 180o apart

The molecular shape is linear

:
C
O
:
: :
O
79
80
Fig. 12-2a, p. 325
Atoms with 3 Sets


When an atom has 3 sets around it, the 3 sets
will be 120o apart due to e- repulsion.
When the 3 sets are bonded atoms, the
molecular shape is trigonal planar
When 2 sets are BA and 1 set is an LP, the
molecular shape is bent.
:
H
:
O
:
H
:O
:
B
N
:

H
81
82
Fig. 12-2b, p. 325
Atoms with 4 Sets


When an atom has 4 sets around it, the 4 sets
will be 109.5o apart
When the 4 sets are bonded atoms, the
molecular shape is tetrahedral

When 3 sets are BA and 1 set is an LP, the
molecular shape is trigonal pyramidal

When 2 sets are BA and 2 sets are LP, the
molecular shape is bent.
83
84
Fig. 12-2c, p. 325
85
86
87
Atoms with 4 Sets



In CH4, the shape is tetrahedral
In NH3, the shape is trigonal pyramidal
In H2O, the shape is bent
H
:
H
H
H
H
:
:
N
C
O
H
H
H
H
88
89
Fig. 12-5, p. 328
90
# esets
molecular shape
bond
angle
2
2BA: linear
180o
3BA: trigonal planar
120o
2BA, 1LP: bent
<120o
4BA: tetrahedral
109.5o
3BA, 1LP: trigonal pyramidal
<109.5o
2BA, 2LP: bent
<109.5o
3
4
91
Electronegativity & Bond
Polarity




Electronegativity is the ability to attract e-s
The most electronegative element is F
The closer on the periodic table to F, the
higher the electronegativity
Electronegative elements “pull” e- density
towards themselves.
92
93
Bond Polarity
You can show bond polarity in two ways,
with partial charges or with polarity arrows
H-F:
: :
: :
d+ d-
H-F:
94
95
Example

:
For BCl3, draw partial charges on all the
atoms
d: Cl :
d -:
+
d
B
Cl :
:Cl :
:
:

d-
:
For BCl3, draw polarity arrows next to all
the bonds
: Cl :
B
: Cl :
:Cl :
:
:
96
Electronegativity & Bond
Polarity

There are 2 types of covalent bonds


nonpolar covalent bonds
polar covalent bonds
97
Electronegativity & Bond
Polarity


In a nonpolar covalent bond, the 2
nonmetal atoms are the same
In a polar covalent bond, the 2 nonmetal
atoms are different.
98
99
100
101
Electronegativity & Bond
Polarity

Ex. Electronegativities (H=2.1, Cl=3.0)



Is an H-H bond nonpolar covalent or
polar covalent?
Is a Cl-Cl bond nonpolar covalent or
polar covalent?
Is an H-Cl bond nonpolar covalent or
polar covalent?
102
103
Polarity of Molecules
You determined whether a bond was polar
covalent or nonpolar covalent
 Using that information and the correct
shapes, you can determine whether a
whole molecule is polar or nonpolar.
 Remember, polarity of bonds and polarity
of molecules are different

104
Review: Polarity of Bonds

Draw BF3 and NF3 in the correct shapes.
Draw a polarity arrow next to each bond.
:
:
:F:
:
:
:F:
:
F:
F:
:
:
:
:F
:
:F
:
B
:
N
105
Polarity of Molecules
To determine if a molecule is polar or
nonpolar, add the polarity arrows.
 The polarity arrows cancel (have no
overall pull) in a nonpolar molecule
 The polarity arrows demonstrate an overall
pull in one direction in a polar molecule

106
Polarity of Molecules

Determine whether BF3 and NF3 are polar
or nonpolar.
:
:
:F:
:
:
:F
:F:
:
F:
:
:F
F:
:
:
:
:
B
:
N
In BF3, the polarity arrows cancel. The molecule is
nonpolar.
In NF3, the arrows don’t cancel. There is overall pull
107
and the molecule is polar.
Notes on Polarity of
Molecules
You must draw the structure in the correct
shape to get polarity of molecules correct
 Polarity of bonds is different than polarity
of molecules
 BF3 has polar covalent bonds, but BF3 is a
nonpolar molecule
 NF3 has polar covalent bonds and is a
polar molecule.

108
Notes on Polarity of
Molecules
The size of the polarity arrow represents
the relative difference in electronegativity
 A B-F bond would have a bigger polarity
arrow than a B-Cl bond
 When polarity arrows cancel, both the size
and direction are taken into account.

109
Examples
Draw CHCl3 and CCl4
:

: Cl :
H
:
C
Cl :
:
:

: Cl
: Cl
:
:

Cl :
:
:

:
:
:

:
:
: Cl
: Cl
C
What are the approx. bond angles? 109.5o
Which molecule contains nonpolar covalent
bonds? neither
Which molecule contains polar covalent bonds? both
Which molecule is polar? CHCl3
110
111
Fig. 12-10, p. 335
Examples: Draw Each One
and Answer the Questions
H2O
CH3NH2
PCl3
C2H4
a) Does it contain nonpolar covalent bonds?
b) Does it contain polar covalent bonds?
c) Is the molecule or ion polar or nonpolar overall?
O
C
N
H
: Cl :
:
a) no
b) yes
c) polar
:
H
: Cl
C
:
H
C
Cl :
:
H
H
:
P
:
H
H
:
:
:
H
H
H
H
a) no
b) yes
c) polar
a) no
b) yes
c) polar
yes
a)
b) yes
c)112nonpolar