CHAPTER 3 – CHEMICAL BONDS
IONS – Particles with unequal number of protons &
electrons
i.e.
Na
sodium
atom
Na+
sodium
ion
+
e(lose an electron)
Two Kinds of Ions:
I)
CATIONS
 Atoms that lose 1 or more electrons
 Positive ions (more protons than electrons)
K
potassium
atom
K+
+
potassium
ion
(
(
(
(
p)
e -)
p)
e-)
charge is ____
Ca
calcium
atom
Ca2+
+
calcium
ion
(
(
(
(
p)
e-)
p)
e-)
e(lose an electron)
2e(lose two electrons)
charge is ____
Naming Cations: name of element plus word “ion”
II) ANIONS
 Atoms that gain 1 or more electrons
 Negative ions (more electrons than protons)
Cl
+ echlorine (gain an electron)
atom
(__ p)
(__ e-)
(__ p)
(__ e-)
O
oxygen
atom
+ 2e(gain 2 electrons)
(__p)
(__e-)
(__p)
(__e-)
Clchloride
ion
charge is ___
O2oxide
ion
charge is ___
Naming Anions: replace ending of name with “ide” plus
word “ion”
Atoms & their Ions
I) The kinds of elements that form cations and anions:
1) Metals form cations
2) Nonmetals form anions
(carbon and boron do not form ions)
II) Atoms & Ions have different properties
i.e. lithium (Li) (soft black metal reacts w/ H2O, poison)
lithium ion (Li+)
(Li2CO3) (white powder, drug to treat manic depress)
THE OCTECT RULE
 Explains the charge on ions.
 Atoms and ions are most stable when they have a
complete outer shell of eight electrons.
(Noble-Gas wanna-be’s)
i.e.
Na 1s22s22p63s1 (outer shell has 1 e-)
Na+ +
Na
Na+
i.e.
e-
1s22s22p6 (outer shell has 8 e-)
[Ne]
O
1s22s22p4 (outer shell has 6 e-)
O
+
O2-
2e-
O2-
1s22s22p6 (outer shell has 8 e-)
[Ne]
Preferred Charges of Monatomic Ions
Periodic Table Groups:
IA
+1
Na+
Li+
IIA
+2
Mg2+
Ca2+
IIIA
+3
Al3+
IVA
VA
-3
N3-
VIA
-2
O2S2-
VIIA
-1
FCl-
VIIIA
0
He
Ne
Octet Rule (some reasons why it is not a perfect rule):
1. Concentrated charges are not stable.
2. Hydrogen can only acquire 2 electrons.
3. The octet rule can’t be applied to transition elements
because they are too far removed from a noble gas
structure.
Write the electron configuration for F-
IONIC BONDS
 Attractions between opposite charged ions holds
compound together.
 Bonding caused by transfer of electrons.
 Ionic compounds usually formed between metals
(positive ions) and nonmetals (negative ions).
 Electrically neutral: positive and negative ions
attracted to each other in equal ratios, so charges
cancel each other out.
 Not a distinct molecule, but a ratio of ions
i.e.
Na+
+
Cl-
forms
NaCl
(sodium chloride)
Predicting Ionic Formulas
1. Write down the symbols with their charges of both the
cation and the anion.
i.e.
given calcium ion and chloride ion
Ca2+
Cl-
2. The subscripts can generally be arrived at by “crossing”
the charges.
i.e.
Ca2+
Cl-
CaCl2
Ca2+
= +2
2Cl= -2
Net charge
0
3. Remember that all subscripts must be reduced to lowest
terms.
i.e
Zn2+
O2-
Zn__O__
(zinc oxide)
reduce subscript ratio:
Zn2+
=
O2=
Net charge
_______
What is the compound formed from sodium ion and iodide
ion?
=
=
Net charge
What is the compound formed from magnesium ion and
chloride ion?
=
=
Does carbon form ionic compounds?
COVALENT BONDS
 Two atoms share a pair of electrons to form a covalent
bond.
 Usually form between nonmetals.
 Form discreet molecules
H.
(dot represents valence electron)
i.e. hydrogen
H.
H.
H . .H
H2
same as helium
1s2
i.e. chlorine, Cl2
..
..
:Cl:
+ :Cl:
..
[Ne]3s23p5
..
1s2
..
..
:Cl . . Cl:
..
..
[Ne] 3s23p6
(octet)
Lewis Structures – show outer shell electrons (non-bonding
electrons) as dots and covalent bonds (bonding electrons)
as lines.
i.e.
H-H
..
..
:Cl
– Cl:
..
..
Each nonmetallic atom has a strong tendency to form a
particular # of covalent bonds.
Number of bonds formed by selected elements in neutral
molecules
Group
No.
Lewis
Form.
No. of
Bonds
1A
2A
3A
.
.
Be.
.
Li
1
2
.
B.
3
4A
.
.
C.
5A
6A
7A
8A
.
N:
.
..
O:
..
:F:
..
:Ne:
.
.
.
.
.
..
4
3
2
1
0
Rules for drawing Lewis structures:
1. Find out how many atoms of each kind are in the
molecule.
i.e. H2O
2H
+
O
2. Write down electron dot formula for each atom. Each
atom has a number of electrons equal to its group
number. Count the number of outer shell electrons for
the molecule.
.
H.
H.
:O:
.
Total e- for molecule:
___ + ___ + ___ = ___
3. Insert the electrons in pairs as either bonds or nonbonding pairs, making sure no atom gets no more than
eight electrons (hydrogen gets no more than two).
.
2H +
..
..
:O:
H :O : H
..
..
non-bonding pair of electrons
..
H -O - H
..
bonding pair of electrons
Examples:
Draw the Lewis Structure for Methane, CH4
Draw the Lewis Structure of nitrogen triiodide, NI3
Example:
Draw the Lewis Structure of carbon tetrachloride, CCl4
General differences between Ionic and Covalent Bonds
Ionic Bond
Transfer of emetal to non-metal
ratio of ions
Covalent Bond
share enon-metal to non-metal
distinct molecule
Example:
Are these ionic are covalent bonds?
NaF
C2H3OH
Polyatomic Ions
Ions containing more than one atom
i.e. hydroxide ion, OH[O - H]ammonium ion, NH4+
+
H
H-N–H
H
Polyatomic ions (cont.)
Example:
What is the compound formed from calcium ion and
hydroxide ion?
What is the compound formed from sodium ion and
carbonate ion?
Naming Covalent Compounds
 1st name more metal-like element, then name second
element by changing ending to ide.
 Use prefix to show number of atoms of each element.
Prefixes
mono
di
tri
tetra
1
2
3
4
(if only 1 atom of 1st element, mono is emitted)
Example:
Formula
Name
CO
____________________
N2O3
____________________
CBr4
_____________________
NAMING IONIC COMPOUNDS
Type I: Binary Ionic Compounds (Binary - 2 elements)
 Name positive ion (cation) first, then negative ion
(anion)
 Cation is just the name of the metal.
 Anion is nonmetal name with ending changed to ide.
Example:
NaCl
__________________
BaCl2
__________________
Type II: Binary Ionic Compounds: B metals & south of
metal/nonmetal boundary
 Metals that form positive ions with more than one
possible charge are named with roman numerals.
 Name cation (metal), charge of cation in roman numerals
in parenthesis, name anion (nonmetal) with ending
change to ide.
 Metal cation charge is obtained from the sum of the
nonmetal anion charge.
Example
Sn
Tin
Sn2+
Tin(II)
SnCl2
Tin (II) Chloride
SnCl4
________________
PbO
________________
PbO2
________________
Sn4+
Tin(IV)
Ionic Compounds containing Polyatomic Ions:
 Name the same as ionic compounds using polyatomic
ion name
Example:
NaNO3
_____________________
FeSO4
_____________________
Ba(OH)2
_____________________
CaCO3
_____________________