Chemical Bonding
Chem I: Chapters 4, 5, 9
Chem IH: 7, 8, 9
Unit Objectives
To be able to:
• Explain why some elements react (form bonds.)
•
Explain the difference between an ionic & a
covalent bond.
•
Demonstrate e- reconfiguration when a simple
compound is formed.
•
Explain how interparticle forces affect the
properties of ionic & covalent compounds.
What is Happening?
Hydrogen balloon burning
2H2 + O2  2H2O
sodium metal & chlorine
Na + Cl  NaCl
sodium iodide & mercury
(II) chloride
2NaI + HgCl2  2NaCl + HgI2


Watch the videos.
What is
happening in all
of these
reactions?
The Chemical Bond

The force that holds
two atoms together

Occurs using
valence electrons
Lewis Dot Diagram
 Definition:
System of showing
the valence e-s for an atom
 Help us predict bonds
Lewis Dot Diagram, cont.
1) Element symbol in middle
2) Valence e-s represented by dots
 Place v.e.-s around the element symbol in 4
locations
Above
Below
Left
Right
 Don’t pair up any, until 1 in each location.
Lewis Dot Diagram, cont.



Practice:
Together: let’s do LDD for Hydrogen,
helium,
You practice: lithium, beryllium, boron,
carbon, nitrogen, oxygen, fluorine, neon.
Lewis Dot Diagram of Main
Group Elements
The Noble Gases





All occur in nature
BUT no compounds containing them are
ever found in nature
Common denominator is that they all have 8
valence e-s. (*except He, which has 2)
This is what makes them stable/unreactive
This is called “Noble Gas Configuration”
(NGC)
All “Other” Elements
 All
other elements “want”
NGC, so they can be stable.
Atoms can Get NGC in one of
two ways
1. Lose/gain e-s (IONIC bond)
 This occurs when the 2 atoms in
the bond pull on their e-s
w/different strengths
 Big EN difference
 Typically occurs btwn a _____ &
a _____.
Atoms can Get NGC in one of
two ways (cont.)
2. Share e-s (COVALENT bond)
 This occurs when the 2 atoms in
the bond pull on their e-s w/the
same (or similar) strength
 Small EN difference
 Typically occurs between 2
___________.
3 “Classes” of Elements
(Review- Do Not Copy)

Metals = pink
Conductors? Yes!
Hold e-s? Loosely
How many V.E’s? 1-3

Nonmetals = green
Conductors? No!
Hold e-s? Tightly
How many V.E.’s? 5-7

Metalloids = blue
“In between”
Ions & the Octet Rule

Ions are charged particles that have lost or
gained e-s to satisfy the octet rule (8 e-s)

They will typically form based on what
requires the smallest gain or loss of e-s to
complete an octet.

Ex: Na  Na+ + eEx: Cl + e-  Cl-

Ions & the Octet Rule, cont.

This also means that atoms will typically
obtain the NGC of the nearest *noble gas

“Nearest” means the one with the closest
atomic number

Ex: Na obtains the NGC of Neon, not Argon
b/c Neon’s atomic # is 10, while Argon’s is
18
Formation of Ions
 The
charge on an ion is called
its “oxidation number”
Formation of Ions, cont.

Metals tend to lose electrons
 Have + oxidation number
 Called “cations”
 Metal ions are given the element
name
 Ex: Na+ = “sodium ion”
Formation of Ions, cont.

Nonmetals tend to gain electrons
 Have – oxidation number
 Called “anions”
 Nonmetal ions are given the
element name w/an “-ide” ending
 Ex: O2- = “oxide ion”
TO DO: Label Your Periodic
Table

Label Groups 1, 2, 3, 16, 17 w/the
oxidation number of each group.
Group # Oxidation #
1
+1
2
+2
3
+3
16
-2
17
-1
Practice

Together, write the arrow orbital diagram for
a sodium atom.

Now draw the arrow orbital diagram for a
sodium ion.

Identify the noble gas that has the same
notation as a sodium ion.

Write the symbol for a sodium ion
Formation of an ionic bond
 When
e-s are lost by 1 atom they are
gained by another. Therefore, cations &
anions are formed at the same time.
Ex: Na & Cl
Formation of an ionic bond, cont.

The attraction between + and - ions is what
forms bond.
Cl-1 Na+1 Cl-1 Na+1 Cl-1
Na+1 Cl-1 Na+1 Cl-1 Na+1
Cl-1 Na+1 Cl-1 Na+1 Cl-1
Na+1 Cl-1 Na+1 Cl-1 Na+1
Practice
1. Draw Lewis Dot Diagrams for sodium and
chlorine ATOMS.
2. Show how e-s rearrange to form sodium &
chlorine IONS.
3. Write the formula (cation, then anion)
4. Name this compound (cation, then anion)
5. (BONUS: What NG is each ion like?)
Formation of an ionic bond, cont.

Note: you will not always have a 1:1 ratio of
+ to - ions.
 Ex: MgI2 -see next slide
Formation of MgI2
..

..
.Mg. + :I: → Mg.+ + :I: - (are they happy?)
.
..
.Mg. +
..
:I:
.
..
..
:I: → Mg2+ + :I: .
..
..
:I:..
Formula Unit
 (Def):
Lowest ratio of ions in
an ionic compound
Writing a Correct Ionic Formula
1.The symbol for the cation is always listed
1st.
2. The symbol for the anion is always listed
2nd.
3. Include subscripts that show how many
cations and anions are present in a Formula
Unit.
4. Ensure they are in the lowest ratio possible.
Our Example: MgI2
2 Techniques to Determine
Correct Ratio of Cations to
Anions
 1. Use Lewis Dot Diagrams and
rearrange electrons until all ions
are “happy.” (learned this already)
 2. Use oxidation #s of cation &
anion to calculate the ratio of
ions to create a neutrally
charged compound.
Technique #2: Using Oxidation
#s to Write Formulas for Ionic
Compounds
Step 1. Identify the
oxidation # on the cation
& anion.
LecturePLUS Timberlake
29
Using Oxidation #s to Write
Formulas for Ionic Compounds
Step 2. A compound has NO
CHARGE on it, so a formula
must have equal numbers of
+ & - charges. (use the LCM)
LecturePLUS Timberlake
30
Using the LCM to Write Ionic
Formulas (Practice)



Ex: Li & F
Ex: Li & O
Ex: Al & O
LecturePLUS Timberlake
31
Polyatomic Ions





(Def): Charged particles containing more
than one element!
Ex: SO 3 2- = “sulfite”
See Table 9.3 on p 257 of text (ChemIH)
See Table 5.2 on p 159 text.
COPY THE APPROPRIATE TABLE ONTO
YOUR P. TABLE OR INTO YOUR NOTES.
Writing Formulas for I.Cpds
Containing Polyatomic Ions
Step 1. Identify cation & anion
Ex: aluminum sulfite
 Aluminum = cation
 Sulfite = anion
LecturePLUS Timberlake
33
Writing Formulas for I.Cpds
Containing Polyatomic Ions, cont.
Step 2: Determine the
oxidation # on each ion. (found
on a table for polyatomics)
Ex:
3+
aluminum = Al
sulfite = SO3 2LecturePLUS Timberlake
34
Writing Formulas for I.Cpds
Containing Polyatomic Ions, cont.
Step 3: Write a balanced
formula
If there is more than 1 of a
polyatomic ion, use
parentheses, then a subscript
Ex: Al2 (SO3)3
LecturePLUS Timberlake
35
Cross-Over Method

“Shortcut” version of using oxidation #s to
write formulas
Step 1: Take the charge on the cation
and use it as the subscript on the anion
Step 2. Take the charge on the anion and
use it as the subscript on the cation
 Step 3: Reduce the subscripts, if
necessary
LecturePLUS Timberlake
36

Oxidation #s of Transition
Metals (Don’t Copy!)
The d sublevel e-s are so close to
the actual valence e-s, they
sometimes act like valence e-s!
 See Table 5.4 on p 164 of text:
Common Ions of Select Transition
Metals
 Ex: Fe 2+ & Fe 3+
 Write the e- configuration
LecturePLUS Timberlake
37
Ionic Compound w/Transition
Metals


Transition metals may have multiple
oxidation #s!
You must be told the oxidation #
 See Table 9.2 on p 255 of text (ChemIH)
 See table Table 5.4 on p 164 of text (ChemI)
Writing Formulas for Ionic Cpds
containing Transition Metals
Step 1. Identify the cation & anion
LecturePLUS Timberlake
39
Writing Formulas for Ionic Cpds
containing Transition Metals, cont.
Step 2. Determine the oxidation #s
on the cation & anion
 The oxidation # of the cation is
given in the name ex: lead (IV) =
Pb4+
 The Roman numeral is the
oxidation#
LecturePLUS Timberlake
40
Writing Formulas for Ionic Cpds
containing Transition Metals, cont.
Step 3. Write a neutrally charged
formula .
LecturePLUS Timberlake
41
“Isoelectronic”


Term used to describe atoms/ions with the
same e- configuration
Ex: F- and Ne
 Both have 2 e-s in the 1st energy level
 Both have 8 electrons in the 2nd energy level

Ex: He and H Both have 2 electrons in the exact same
arrangement
Formulas

Tell us:
 the elements that make up the compound
 the # of atoms of each element in a unit of the
compound

The smallest unit of an Ionic Compound is
called a “Formula Unit”

The smallest unit of a Covalent compound is
called a Formula Unit or “Molecule”
Quiz

Ionic bonds are formed
by the ______ of
electrons.

CO is a/n
ionic/covalent
compound.

Covalent bonds are
formed by the
________ of electrons.

NaF is a/n
ionic/covalent
compound.