Properties of Ionic and
molecular/covalent bonds
Review of Ionic Compounds
In an ionic compound,
• One element [non-metal], can strongly pull
electrons away from other element and become a
negative ion [anion],
• as the element fills it’s valence shell
• The other element [metal], is weaker at holding it’s
electrons and loses valence electrons & becomes a
positive ion [cation].
Non-Metal
Anions
Metal
Cations
Noble Gases
Properties of Ionic Compounds
1. hard & brittle
2. crystal lattice
structure Na
Cl
Formula unit:NaCl
Properties of Ionic Compounds
3. high melting and boiling
point
4. solid at room temperature
Compound
H 2O
Melting
point (°C)
O
Boiling
point (°C)
100
NaCl
800
1465
MgCl2
714
1412
Properties of Ionic
Compounds
1. Electrolytes
(Ionic compounds can
conduct electricity in the
liquid state or dissolved in
water.)
*Nelson Chemistry
Lewis Structures
ON
1
2
H
3
He
4
Li
11
5
Be
12
Na
19
6
B
13
Mg
7
C
14
Al
Si
9
16
P
17
S
Se
*neutral
Ne
18
Cl
35
34
Ca
10
F
O
N
15
20
K
8
Ar
36
Br
Kr
Ionic Structures
1
2
He
fill itselectrons.
outer shell.
Metal losesNonmetals
all of its outer
3
4
Na
2
Mg
3
8
13
3
14
15
2
3
16
2
Ca
17
Ne
18
Cl
2
Se
10
F
S
P
34
2
9
O
N
Al
20
K
7
Be
12
19
6
2
Li
11
5
35
Ar
36
Br
Kr
Practice: Na2O
Lewis Structure for the atom:
Subscript represents
the number of
‘Na’ ion in this bond.
O
Na
Lewis Structure for the ionic bond:
Na
O
2
Na
2
Na
Coefficient represents
the number of
‘Na’ ion in this bond.
O
2
Individually : Practice MgF2
Lewis Structure for the atom:
F
Mg
Lewis Structure for the ionic bond:
F
Mg
2
F
Mg
2
2
F
Properties of covalent
compounds
Covalent compounds
• A chemical compound composed of molecules
made up of two or more non-metallic elements
held together by covalent bonds.
• A covalent bond is the result from the sharing of
a pair of electrons by two atoms
Covalent compounds
• Tug of war for electrons
Covalent compounds
• How do you know a compound is covalent?
• Nonmetal + nonmetal
• Similar electronegativity
(∆EN < 1.7)
Nonmetals
*Q?
Electrons
aren’t
shared
equally!
POLARITY
Covalent compounds
•0.5 < ∆EN < 1.7 = polar covalent bond
•0.0 < ∆EN < 0.5 = very slightly polar
covalent bond
•∆EN = 0 non-polar covalent bond
•Electronegativity difference is sometimes
called the ionic character.
Practice
• Example: Calculate the electronegativity
difference between O2. Is the bond a
covalent or ionic bond?
∆EN = ENO – ENO
∆EN = 3.5 – 3.5
∆EN = 0
Non-polar
Therefore the bond between O and O is covalent.
Practice
1.
Calculate ∆EN between Cl and C.
∆EN = ENCl – ENC
∆EN = 3.0 – 2.5
∆EN = 0.5
slightly polar
Therefore the bond between Cl and C is covalent.
*EN is listed on pg. 25 textbook
O
δH
δ
ENH=2.1
∆ENH=ENO – ENH
= 3.5 – 2.1
= 1.4
H
+
ENO=3.5
Water is a polar
molecule.
Melting point and boiling point
•Determine by the strength of attractive
forces between the particles.
•Polar covalent molecules have a medium
mp/bp because of dipole-dipole
attraction.
Intermolecular forces
δ
δ
-
O
H H
δ
δ-
O
H H
δ+
O
H H
δ
+
δ
-
+
-
O
H H
δ+
δ-
O
H H
δ+
Melting point and boiling point
•Non-polar covalent molecules have a low
mp/bp.
•positive nuclei of atoms in one molecule
can still be attracted to the electrons of a
neighbouring molecule.
🢡 These forces are very weak!
Chart
Consider the following:
COMPOUND
ethanol
ammonia
cesium bromide
hydrogen gas
magnesium oxide
methane
nitrogen gas
sodium chloride
water
BOILING POINT
( °C)
+78.3
+33.3
+1300
-253
+3600
-161
-196
+1465
+100
Consider the following:
COMPOUND
hydrogen gas
nitrogen gas
methane
ammonia
ethanol
water
cesium bromide
sodium chloride
magnesium oxide
FORMULA BOILING POINT
( °C)
H2
-253
Non-polar
N2
-196
covalent
CH4
-161
NH3
+33.3
Polar
C2H5OH
+78.3
covalent
H2O
+100
CsBr
+1300
NaCl
+1465
Ionic
MgO
+3600
Electrical Conductivity
• Need charged ions that are free to move
around to conduct electricity
• Only possible for ionic compounds (liquid
state, dissolved in water). For this reason, they
are called electrolytes.
• In covalent compounds , electrons do not
leave an atom completely so they do not
conduct electricity. They are called
non-electrolytes.
Water solubility
• H will be attracted to negative ion
or a partially negative atom.
• O will be attracted to positive ion or a partially
positive atom.
IONIC AND POLAR COVALENT COMPOUNDS
ARE WATER SOLUBLE.
NON-POLAR COVALENT COMPOUNDS ARE
NOT WATER SOLUBLE.
Physical Properties of
Ionic and Molecular Compounds
Property
Ionic Compound
Molecular
Compound
State at ambient temp.
Crystalline solid
Solid, liquid, or gas
Physical properties
Hard, brittle
Solids can be soft, waxy,
flexible, or crystalline
Relative melting point/
boiling point
High
Low to medium
Electrical conductivity
(dissolved in water, liquid
state)
Good
Poor (for most molecular
compounds)
Soluble in water
Yes
Maybe
Ionic Compounds
Covalent Compounds
transfer of electron(s)
sharing of electron(s)
metal + nonmetal
nonmetal + nonmetal
large difference in electronegativity
similar electronegativity
AlCl3
H2O
strontium fluoride
sulfur hexafluoride
naming may involve Roman Numerals
(I, II, III, IV,…)
formula is reduced to lowest ratio
naming may involve prefixes
(mono, di, tri, tetra,…)
formula is not reduced to lowest ratio
may contain polyatomic groups
may be polar/have dipole-dipole forces
high melting and boiling points
low to medium melting and boiling points
water soluble
may be water soluble
electrolytes
non-electrolytes
crystal lattice structure
can be solid, liquid or gas at room temp.
solid at room temp.
Ionic Structures
Transfer of electron
Na
Cl
Transfer of electron
Na
Cl
Covalent Structures
Sharing of electrons
lone pairs
(not involved in bonding)
14 valence electrons
F
F
Sharing of
electrons
• unpaired electron
(bonding electron)
• bonding capacity
(number of bonds that can form)
F
F
• bonding pair
(involved in bonding)
• single bond
(one pair of electrons involved)
Covalent Structures
Sharing of
electrons
8 valence electrons
H
O
H
• unpaired electron
Sharing of
electrons
H
lone pairs
O
H
• bonding pair
• single bond
Covalent Structures
12 valence electrons
O
O
Sharing of
electrons
O
O
O
O
• unpaired electron
lone pairs
• bonding pair
• double bond
Covalent Structures
10 valence electrons
N
N
Sharing of
electrons
N
N
N
N
• unpaired electron
lone pairs
• bonding pair
• triple bond
Covalent bonds
• Single bond: one pair of electrons are shared.
• Double bond: two pair of electrons are shared.
• Triple bond: three pair of electrons are shared.
Exceeding Octet Rule
Example: PCl5
Cl
Cl
Cl
P
Cl
40 valence electrons
Cl
Cl
Cl
Cl
P
Cl
Cl
Method for drawing the Lewis Structures of
Covalent compound
Arrange the elements so that the least EN element
is in the middle (largest bonding capacity). Spread
the remaining atoms around the central atom.
2. Count all the valence electrons
(ve-) for all the atoms in the molecule.
1.
Method for drawing the Lewis Structures of
Covalent compound
-
3.
Place two ve s between the central atom and each of
the surrounding atoms to form a single bond.
4.
Place lone pairs of ve-s around each of the
surrounding atoms. (Octet Rule)
Method for drawing the Lewis Structures of
Covalent compound
5.
6.
-
If there are more ve s, place the remaining around
the central atom to complete the octet.
If you still have more ve-s
-double check the number of ve
-check if central atom is in Period 3
(may have more than 8 ve-s)
Method for drawing the Lewis Structures of
Covalent compound
7.
-
If you do not have any more ve s and the central
atom still does not have a complete octet then share
lone pairs from outside atoms to form double or
triple bonds.
Practice drawing the Lewis Structure
1.
2.
3.
4.
5.
6.
7.
CO2
PH3
CF4
NH3
Cl2
PCl3
HCl
Practice drawing the Lewis Structure
1.
2.
3.
4.
5.
6.
7.
SF6
NO2
I2
H2S
CCl4
SiF4
H2
Structural Formula
• Use a dash to represent covalent bonds
• bonding pair
(represented by dash)
F
F
Sharing of
electrons
• Modified structural
formula shows lone pairs
F
F
F
F
Structural Formula
H
O
H
Sharing of
electrons
H
O
H
• Modified structural
H
O
H
Covalent Structures
O
O
Sharing of
electrons
O
O
• Modified structural
O
O
Structural Formula
N
N
Sharing of
electrons
N
N
• Modified structural
N
N
Exceeding Octet Rule
Example: PCl5
Cl
P
Cl
Cl
Cl
Cl
Cl
Cl
Cl
P
Cl
Cl
• Modified structural
Draw the Structural Formula
1.
2.
3.
4.
5.
6.
7.
CO2
PH3
CF4
NH3
Cl2
PCl3
HCl
Draw the Structural Formula
1.
2.
3.
4.
5.
6.
7.
SF6
NO2
I2
H2S
CCl4
SiF4
H2