Chapter 8
Covalent Bonding
Covalent bonding …….
• Usually forms between two nonmetals
(takers)
• Neither want to give up their
electrons but are willing to share
electrons
Exception: Hydrogen
•Hydrogen has one electron, but only
needs one more to be “happy”
Hydrogen and a nonmetal …..neither wants
to give up their electrons and neither has
enough pull to take the other’s so they share
a pair of electrons
In a covalent bond the…
-shared electrons are attracted to
adjacent nuclei
+
+
Covalent Bonding
Covalent Bonds form
molecules
Molecule = smallest part of
a covalent compound
(* remember: Ionic Compounds form
formula units)
That’s why…….Covalent
compounds are also
called molecular
compounds
Naming Covalent Compounds
Binary (2-element) compounds
-similar to ionic, but indicate the
number of atoms using prefixes
Prefix
MonoDiTriTetraPentaHexaHeptaOctaNona
Deca-
Meaning
1
2
3
4
5
6
7
8
9
10
-if only 1 atom of 1st element, then
no prefix is used
Ex.
CO
Carbon monoxide
CO2
Carbon dioxide
-if more than 1 atom of 1st element,
then use prefix
N2O4
Dinitrogen tetraoxide
Ws. Naming Molecular Compounds
Ws. Name the following Molecular
Compounds
Hydrogen Compounds can form
Acids
• Remember…..Hydrogen is the
exception to most rules
• Hydrogen has 1 electron but only
needs 1 more to be happy so it acts
like a nonmetal
• Hydrogen doesn’t want to give up it’s
one electron but it is willing to share
it.
• When hydrogen combines with an
anion a covalent compound is formed
When these compounds are
dissolved in water…..
…..they become acids.
What makes them an acid?
• Hydronium ions are formed
How to Name Acids
• Start with ionic compound
name.
• Then follow the 3 rules
Naming Acids
Rule #1 (Binary Acids)
• When anion ends in “ide”, the
acid name begins with “hydro”
and then ends in “ic”, then
“acid”
• Ex. Hydrogen chloride (HCl)=
hydrochloric acid
Hydrogen sulfide (H2S)
=hydrosulfuric acid
Naming Acids
Rule #2 (Tertiary Acids)
• If anion ends in “ate”, the acid
name is the stem of the anion with
the suffix “-ic” followed by the
word “acid”
• Ex. Hydrogen nitrate (HNO3) =
nitric acid
Naming Acids
Rule #3 (Tertiary Acids)
• When anion ends in “ite” , the
acid name is the stem of the
anion with suffix
“-ous”
followed by the word “acid”
• Ex. Hydrogen sulfite (H2SO3) =
sulfurous acid
Ws. Name the Following Acids
Ws. Formula Writing
Molecule
CO
H2O
1 molecule of
carbon monoxide
1 molecule of
water
• Ex.
How many molecules of water???
4 molecules of water
4 H2O
Coefficient – the # of molecules
or # of formula units .
The number covalent bonds
that will form depends on the
# of valence electrons
*Remember each atom is trying to
achieve noble gas configuration
(full outer shell)
7 valence electrons wants to share 1 pair
6 valence electrons wants to share 2 pair
5 valence electrons wants to share 3 pair
Chlorine atoms each
have 7 valence
electrons
….they each want one
more so they will share
one pair of electrons
Formation of Bonds
Single Covalent Bonds – 1 shared
pair of electrons
Cl2
Single bond- 1 shared pair of electrons
F
and
F
F
F
Double bond-2 shared pairs of electrons
O
and
O
O
O
Triple bond-3 shared pairs of electrons
N
and
N
N
N
Lewis Dot Diagram of
Covalent Compounds
-you
show the shared pair(s) of
electrons between symbols
Ex. Cl2
Cl Cl
Structural Formulas
• Each pair of shared electrons is
shown as a dash( - )
• Ex. Cl2
Cl
Cl
Lewis Dot Diagram
Cl-Cl
Structural Formula
Be careful with
Hydrogen (H2)
*Remember hydrogen
only needs to share one
pair
Hydrogen (H2)
H-H
Diatomic Molecules
• Two different atoms covalently
bonded
• Ex.
CO
OH
Diatomic Elements
-when atoms of same element
covalently bond
Ex.
Cl and Cl
Cl Cl
Diatomic Elements
-elements that exist in pairs when not
bonded to other atoms
(“BrINClHOF”)
Br2
I2
N2
Cl2
H2
O2
F2
bromine
iodine
nitrogen
chlorine
hydrogen
oxygen
fluorine
More examples of single
covalent bonds…
Water H2O
(2 single covalent
bonds)
H
H
O
Hydrogen and chlorine
H-Cl
Methane CH4
( 4 single covalent bonds)
H
H
C
H
H
PCl3 Phosphorus trichloride
( 3 single covalent bonds)
Cl
P
Cl
Cl
Double Bonds
O
O
Carbon dioxide
O
C
O
Lewis Dot Diagram of carbon
dioxide
O
C
O
Triple bonds
N
N
Coordinate Covalent
Bonds
• A coordinate covalent bond is formed
when one atom donates both
electrons to be shared.
Ammonium NH4
+
Coordinate covalent bond
H N H
H
Ammonia NH3
H
Hydrogen
In coordinate bond structural
formula……
An arrow points from the atom donating
the pair of electrons toward the atom
receiving them.
H
H N H
H
When drawing electron dot
diagrams……..
• if an atom is “short” 2
electrons – try a coordinate
covalent bond
H3(PO4)
H3(PO4)
H O
O P O
H
O
H
Coordinate
covalent bond
Bond Polarity
• Nonpolar - When bonding electrons are
equally shared (same electronegativity)
• Ex. Diatomic elements
• Polar
– When one atom has higher
electronegativity ( attractive force) and
pulls electron closer to it. It gains a slight
negative charge and the other atom gains a
slight positive charge
• Ex. H2O
Ws. What is Electronegativity?
Electronegativity Differences !!!!!
• If the difference is….. the type of bond will be..
.4 and below
Nonpolar covalent
Between .4 to 2.0
Polar covalent
Greater than 2.0
ionic
Describing each bond in
the molecule as ….
• Even pull= Nonpolar
Uneven pull = polar
Strong uneven pull = ionic
Showing polarity of individual
bonds
Use differences in electronegativities
Indicated with δ ( lower case Greek
letter delta) and charge.
Overall polarity of Molecules
equals the sum of all the bond polarities
The arrow points to the atom with the
higher electronegativity
Symmetry in Molecules
• Symmetrical molecules are usually
nonpolar. Polar bonds cancel each
other out
• Ex. CO2
Carbon Tetrachloride
Bonds can be polar, yet overall
molecular polarity is nonpolar
Asymmetrical
Molecules
• Asymmetrical molecules are polar if there
are polar bonds in the structure.
• Ex. H2O
Polarity of Water
δ δ
O
H
δ+
H
δ+
VSEPR Theory
• Valence shell electron-pair
repulsion theory
• Because electron pairs repel,
molecules adjust shapes so that pairs
are as far away from each other as
possible
Domains
•
•
•
•
Single bond
Double bond
Triple bond
Lone unshared pair
The # of Electron Domains
determines the Basic Electron
Domain shape
•
•
•
•
•
Linear – 1 or 2 domains
Trigonal Planar – 3 domains
Tetrahedral – 4 domains
Trigonal bipyramidal – 5 domains
Octrahedral – 6 domains
Linear
Trigonal Planar ( flat)
Tetrahedral
Trigonal bipyramidal
Octahedral
Determining the Electron Domain Shape
• Count up all valence electrons
• Start with central atom (C, or Lowest EN,
never H)
• Place other atoms around with maximum
repulsion
• Put 8 electrons around outside atoms
• Any extra electrons go around the central
atom
• Count the number of domains to determine
the basic shape
• **** some compounds do NOT follow the
octet rule
Let’s try some
•
•
•
•
•
•
•
•
•
CS2
BeH2
CO2
CH4
CCl4
NO3NH4+
SiF4
SF4
Molecular geometry
• Shapes are altered if there are
non- bonding pairs of electrons
surrounding the central atom
Bent – can be formed from a trigonal
planar or tetrahedral
Ex. SO2
Ex. H2O
Trigonal Pyramidal-
can be
formed from a tetrahedral
Ex. NH3
Ws. Electron Domain and
Molecular Geometries
Structures and Models
Covalent Bonding:
Molecular Model
Building Lab
Model Colors
•
•
•
•
•
Black – Carbon family
Blue – Nitrogen family
Red - Oxygen family
Green or Purple - Halogens
Yellow - Hydrogen
• Use sticks to show single bonds
• Use springs to show multiple bonds
Formula
Electron
domain
shape/
Molecular
shape
Lewis Dot diagram
* be careful of
shape
Single,
double or
triple
bond ( list
each bond
EN
Differencelist for for
each bond
Bond Type (
polar or
nonpolar –
list for each
bond)
Polarity of
Molecule (polar
or nonpolar)
H2
EA=
D=
NBD=
BD=
Cl2
EA=
D=
NBD=
BD=
EA= valenceelectrons available
NBD= non-bonding domains
D = electron domains
BD= bonding domains
Electron –Domain
Basic Bond Shapes
•
•
•
•
•
Linear
Bent
Trigonal Planar
Trigonal Pyramidal
Tetrahedral
Hints for Lab
Start with Central Atom
• If it has carbon, use “C” as central
atom
• If no carbon, use single atom or atom
with lowest EN as central atom
• Never put hydrogen as central atom
Hints about the Acids
• Do polyatomic ion groups first, then
add the hydrogens
• Use single atom, except Hydrogen,
as central atom
• Usually contain coordinate covalent
bonds
Last Hint !!!!
• If an atom is “short” 2 electrons –
try a coordinate covalent bond
H2(CO3)
Double bond
O
O
C
H
O H
H3(PO4)
H O
O P O
H
O
H
Coordinate
covalent bond
H2(SO4)
H O
O S
H O
O
Coordinate
covalent bonds
H(NO3)
O
O N
H
O
Coordinate
covalent bond
Properties of
Covalent Compounds
• Low melting points (usually below
300oC)
• Boiling points usually lower than ionic
compounds
• Many are liquids or gases at room
temperature
• High to low solubility
• Poor to non-conducting
Covalent Compounds form
Network Solids
• Most covalently bonds substances
melt easily because you just have to
break the weak attractions between
molecule and molecule
• Ex. Ice – Water
– Sugar (C12H22O11)
Covalent crystals
• If covalent compound forms crystals
(repeating pattern)……..
• Requires a lot of energy to break all
the covalent bonds
• Have high melting points
• Ex. diamonds
A diamond ( pure carbon)
Solubility of
Covalent Compounds
• “Like dissolves Like”
• Polar compounds will dissolve
in polar solvents
• Nonpolar compounds will
dissolve in nonpolar solvents
Why don’t water and oil mix?
-Water is polar, oil is nonpolar.
-Water is more attracted to itself
than to the oil.
Why do detergents cause water and oil to
mix?
-detergents are long molecules with
one polar and one nonpolar end.
-the water is attracted to the polar
end and the oil is attracted to the
nonpolar end.
Soap and Detergent
Nonpolar end –attracts
nonpolar oil or grease
Polar end –attracts
(polar)water
Chapter Review
Covalent Bonding
Ionic
Electrons transfer
vs.
Metal and Non metal
Formula units
No prefixes in names
Neutral compound
Called salts
High melting points,
easily dissolved and
conduct when dissolved
Covalent
Electrons shared
Nonmetal and Nonmetal
molecules
Prefixes in names
Neutral compound
If starts with “H” it could
be an acid when dissolved
in H2O
Low melting points, not
easy to dissolve, don’t
conduct electricity
Ws. Bond Prediction
Ws.Naming Compounds
Ws. Name the Following
Compounds
Ws. Naming Compounds
Reference Sheet
Diatomics = 2 atoms of
same element bonded to
each other
BrINClHOF
Diatomic element is linear and Nonpolar
Covalent Bonds – 4 Types
• Single- 1 shared pair of electrons
(1 from each atom)
• Double – 2 shared pairs of electrons
(two from each atom)
• Triple- 3 shared pairs of electrons,
(three from each atom)
• Coordinate covalent – both
electrons of shared pair come from
1 atom
Structural Formula- shows
arrangement of bonds
•
•
•
•
Cl
O
N
C
Cl single
O double
N triple
O coordinate covalent
Electron Dot Diagrams
• Every atom MUST have 8 electrons
drawn around it except “H”.
• “H” needs 2 electrons
Polar vs. Nonpolar – depends
on EN ( electronegativity)
difference
• Nonpolar – shared evenly – EN
difference below .4
• Polar – shared unevenly – EN .4 –
2.0
• Ionic – pulls electron off of atom.
EN above 2.0
Polarity of Bond
• Depends on
electronegativity difference
Polarity of Molecule
• Look at symmetry, then polarity of
the bonds
Know how to name ionic
compounds, covalent
compounds and acids
The End