Download Chapter 9

Chapter 9
Covalent Bonding
Section 9.1
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Atoms bond together because they want a
stable electron arrangement consisting of a full
outer energy level.
Two ways that atoms can bond together are
ionically & covalently.
A covalent bond is a chemical bond that results
from the sharing of the valence electrons.
Covalent bonds are usually formed between
elements close to each other on the periodic
table and nonmetallic elements.
Nonmetals bonded with nonmetals
Section 9.1
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A molecule is formed when 2 or more
atoms bond covalently.
Example
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HI
F2
Practice problems
1. HBr
2. O2
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3. H2O
`
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Diatomic molecules are molecules of like
atoms. Diatomic molecules include
hydrogen, nitrogen, oxygen, fluorine,
chlorine, bromine, & iodine.
Write the formulas & structures for the
diatomic molecules.
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The number of covalent bonds that these
groups form are:
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Halogens  single covalent bond
Group 6A  double/two covalent bond
Group 5A  triple/three covalent bond
Group 4A  four covalent bonds
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Practice
 HF
 OCl2
 H2S
 N2
 PH3
 SiH4
Section 9.1
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Single covalent bonds are also called
sigma bonds, symbolized by the Greek
letter s
A sigma bond results when orbitals
overlap.
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s orbitals can overlap s orbitals
s orbitals can overlap p orbitals
p orbitals can overlap p orbitals
Section 9.1
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Multiple covalent bonds occur when more
than one pair of electrons are shared.
A pi bond, p, is formed when parallel
orbitals overlap to share electrons.
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A double bond is made of 1 sigma bond & 1
pi bond
A triple bond is made of 1 sigma bond & 2 pi
bonds
Practice
Draw the lewis dot structure for each
molecule.
 1. PH3
 2. H2S
 3. HCl
 4. CCl4
 5. SiH4
 6. CO2
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If H2O is water, what is H2O4?
Drinking, bathing, washing, swimming…
Section 9.1
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The strength of covalent bonds depend on
the length of the bond, the distance
between the bonded nuclei.
Bond length is determined by the size of
the atoms & the number of shared
electron pairs.
As the number of shared pairs increases,
the bond length decreases.
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The shorter the bond, the stronger the bond.
Energy is released when a bond forms & energy
is added to break a bond.
Which has a shorter bond? H2 or S2
The amount of energy needed to break a bond
is the “Bond Dissociation Energy”
Among F2, O2, & N2, which would have the
greatest bond dissociation energy?
Least?
Section 9.1
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Endothermic reactionsoccur when a
greater amount of energy is required to
break the existing bonds in the reactants
than is released when the new bonds form
in the product molecules
Exothermic reactions occur when more
energy is released forming new bonds
than is required to break bonds in the
initial reactants
Measuring heat
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Exothermic Rxn
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Endothermic Rxn
Section 9.2
Naming Binary Molecular Compounds
1st element—use entire element name
2nd element—use root word & “ide”
use prefixes to indicate # of atoms for each
element
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prefixes
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mono—1
di—2
tri—3
tetra—4
penta—5
hexa—6
hepta—7
octa—8
nona—9
deca--10
Section 9.2
**NEVER USE mono WITH 1ST ELEMENT**
Example
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N2Cl3
CO2
Practice
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1. P2O5
2. NO2
3. CO
Common names of some molecular compounds—
p. 249
** Worksheet “Naming molecular compounds”
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What is the name for H2O?
What is the name for CH2O?
Sea water
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Naming acids
Binary acids—hydrogen plus one other
element
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Hydro + root of 2nd element + ic acid
1.
2.
3.
4.
HClhydrochloric acid
HBrhydrobromic acid
H2S  hydrosulfuric acid
Hydroiodic acid
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Oxyacids—contain hydrogen & oxygen and
one other element
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Root of other element + ic acid
H2CO3
 H2SO4
 HC2H3O2 
 Phosphoric acid 
 Nitric acid 
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** Worksheet “Naming acids”
Section 9.3
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Structural formulas use letter symbols &
bonds to show relative positions of atoms.
Hydrogen is always a terminal atom
because it can bond with only 1 other
atom.
Resonance is a condition that occurs when
more than one valid Lewis structure can
be written for a molecule or ion.
Resonance
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Example
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HCl
SO2
Practice
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1. SO3
2. O3
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A coordinate covalent bond forms when
one atom donates both electrons to be
shared.
9.4 Molecular Shapes
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Molecular shape is determined by the overlap of
orbitals that share electrons.
The VSEPR model is used to determine the
molecular shape of the molecule. VSEPR stands
for
Valence
Shell
Electron
Pair
Repulsion model.
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F2 has linear shape
CO2 has linear shape
BH3 has trigonal planar shape
CF4 has tetrahedral shape
NH3 has pyramidal shape
H2O has bent shape
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Hydridization is a process where atomic
orbitals are mixed to form new, identical
hybrid orbitals.
Carbon is the most common element that
undergoes hybridization.
The hybrid orbital of carbon is called sp3.
It takes shape to look like a tetrahedral.
9.5 Electronegativity & Polarity
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Remember that electronegativity is
defined as the tendency of an atom to
attract electrons.
Fluorine has the highest EN at 3.98 and
Francium has the lowest EN at 0.7.
Polar/nonpolar
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Polar covalent bond is when electrons are
unequally shared—large difference in EN.
Electrons spend more time around the
element that is more EN. The more EN
element has a partial negative charge. A
polar covalent bond is also called a dipole.
Electronegativity occurs in molecules.
For example H2O & HCl
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Page 263
Polar/nonpolar
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Nonpolar covalent bond is when electrons
are shared equally—have small or no EN
differences. Symmetrical molecules with
balanced charges are nonpolar. (CCl4)
These are pure covalent bonds.
Ionic bonds generally form when EN
differences are 1.7 or greater.
Electronegativity
difference
0.00 - 0.4
Bond Type
0.5 – 1.6
Polar covalent
1.7 – 3.2
ionic
Nonpolar covalent
Polar, Nonpolar, or Ionic?
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Example:
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HCl
Practice:
1.
2.
3.
4.
SCl2
H2S
CF4
CS2
Properties of covalent compoundsp. 266-267
“like dissolves like”
 Many different types of forces between
molecules.
**Worksheet “Shape/polarity of molecules”
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Mainly gases (some liquids), melt/vaporize
easily, hardness varies.
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Oxygen gas, acids, parafinn, graphite,
diamonds