Chapter 22: Chemical
Bonding
Section 1– Electrons and
Chemical Bonding
Chemical bonding – joining of atoms to form new
substances
Chemical bond – interaction that holds 2 atoms
together
Valence Electrons
e- in outermost shell
Determines an atom’s chemical properties
Used to form bonds
Within a group, or family, atoms have the same # of
valence e-
Atoms with fewer than 8 valence e- are more likely to
form bonds than an atom with 8 e-
Types of Bonds
Ionic, Covalent, Metallic
Atoms bond by sharing, gaining or losing e- to have a
filled outermost energy level.
A full set = 2 e- for a few of the elements
A full set = 8 e- for most elements
Which ones? Why?
Section 2:
Ionic Bonds
Bonds form by gaining
or losing e-, resulting in
charged atoms called
ions.
Oppositely charged ions
are attracted to one
another
Metal + Nonmetal
Positive and negative
charges cancel each
other out to form an
overall neutral
compound
Metal Atoms
Have few valence electrons
Usually lose these valence e- and form positive ions
(cations)
Some transition metal ions can have multiple charges. For
example, iron can have a +2 or a +3 charge.
The charge is written as a superscript of the symbol:
Ex. K+, Ca2+, Al3+
Nonmetal atoms
Have almost full valence shells
Tend to gain e- from other atoms and form negative
ions (anions)
The charge is written as a superscript of the formula:
Ex. P3-, S2-, Cl-
Polyatomic Ions
Poly = “many”
Polyatomic = “many atoms”
A group of atoms that behave as a single ion with an
overall positive or negative charge
Treat the polyatomic ion as a single unit with a single
charge.
Writing formulas for
ionic compounds
The number of positive charges and negative charges
must balance in an ionic compound
The formula represents this balance
Subscripts are used to indicate the ratio of elements
in the compound (no “1”)
Writing formulas for
ionic compounds
1.
Find oxidation number (charge) for both parts
a.
b.
c.
For elements in groups 1 and 2, use group #. Boron
family is 3+, Carbon family ± 4, Nitrogen family is -3,
Oxygen family is -2 and halogens are -1.
For cations followed by a roman numeral, the roman
numeral is the oxidation #
For polyatomic ions check the list. Do not change the
subscripts within the polyatomic ion formula.
2. Write symbols. The positive ion first and negative ion
second.
3. Put polyatomic ions in parentheses if more than one is
needed.
4. Use subscripts to designate the number of each part
for the total + and – charges to be =
a. Find the least common multiple of both charges
b. determine the factor needed to get that charge and
use that as the subscript.
a.
Sodium sulfide
g. Sodium acetate
b.
Potassium iodide
h. Zinc(II) carbonate
c.
Lithium oxide
i. Chromium(II) sulfate
d.
Barium fluoride
j. Cobalt(III) iodide
e.
Iron(III) oxide
f.
Copper(II) chloride
Answers
a.
Na2S
f. CuCl2
b. KI
g. NaC2H3O2
c.
h. ZnCO3
Li2O
d. BaF2
i. CrSO4
e.
j. CoI3
Fe2O3
Writing names for ionic
compounds
1.
Write the names of the + and - part of the formula
2.
The + part is the name of the element or polyatomic ion
3.
Check the list of elements to see if it needs a roman numeral.
If so, use the negative part of the formula to figure out the
positive charge on the metal.
4.
To name the second/- part, if it is an element change the
ending to “-ide”
5.
If it is a polyatomic ion, keep the name as is
a.
b.
c.
d.
e.
f.
LiCl
MgCl2
BeO
CaCl2
HgS
SnF2
g. (NH4)3PO4
h. ZnCO3
i. Sn(OH)2
j. Li2SO4
k. KC2H3O2
Answers
a.
b.
c.
d.
e.
f.
Lithium chloride
Magnesium Chloride
Beryllium oxide
Calcium Chloride
Mercury(II) sulfide
Tin(II) fluoride
g. Ammonium phosphate
h. Zinc(II) carbonate
i. Tin(II) hydroxide
j. Lithium sulfate
k. Potassium acetate
Section 3: Covalent and
Metallic Bonds
Covalent bonds are formed when atoms share one or
more pairs of valence e-.
Forms between 2 nonmetals.
Covalent bonds result in the formation of molecules.
Define molecule
Octet Rule
Atoms combine in such a way so as to fill the valence
shell (usually that means 8 e- but could be just 2 e-)
How many bonds?
The number of e- that an
atom needs to fulfill it’s
valence is equal to the
number of covalent bonds it
can form.
Ex. N can make 3 covalent
bonds because it has 5 e- in
its valence shell
Ex. H can make 1 covalent
bond because it has 1 e- its
valence shell.
Diatomic Elements
Certain elements exist as
pairs in nature because that
is how they are most stable.
Di = 2
Just remember Professor
BrINClHOF (Bromine,
Iodine, Nitrogen, Chlorine,
Hydrogen, Oxygen and
Fluorine)
You need to memorize the 7
diatomic elements!!
Practice! Draw a Bohr diagram and
Lewis structure for the following:
Water (H2O)
Diatomic Fluorine (F2)
Silicon tetrafluoride (SiF4)
Double Bonds
When atoms share 2 pairs of e-, it is a double bond
Triple Bonds
When atoms share 3 pairs of e-, it is a triple bond
Naming Covalent
Compounds
Many compounds have common names such as
"methane", "ammonia" and "water”
Simple covalent compounds can be named using
prefixes to indicate how many atoms of each
element are in the formula.
The ending of the last (most negative) element is
changed to -ide.
Naming Covalent
Compounds
Prefixes:
 Mono = 1
 Di = 2
 Tri = 3
 Tetra = 4
 Penta = 5
 Hexa = 6
*If there is just 1 of the first element no prefix is used
Practice
CO2
SiF4
CO
NBr3
P2O5
BCl3
Answers
CO2 – carbon dioxide
SiF4 – silicon tetrafluoride
CO – carbon monoxide
NBr3 – nitrogen tribromide
P2O5 – diphosphorus pentoxide
BCl3 - boron trichloride
Practice
Carbon tetrabromide
Phosphorus triiodide
Bromine
silicon monoxide
Silicon disulfide
Answers
CBr4
PI3
Br2 (Bromine is a diatomic molecule!)
SiO
SiS2
Metallic Bonds
A bond formed by the
attraction between
positively charged metal
ions and surrounding eThink of a metal as being
made up of positive ions
with electrons “swimming”
around keeping the ions
together
Properties of Metals
Because e- can move freely about, metals have
particular propeties.
Conduct electricity well
Metals can be reshaped (ductile, malleable)
Metals can bend without breaking