Covalent Bonding


Between nonmetals
Share valence electrons between atoms

Electron clouds overlap
Ex:
H2O
CH4
NH3
CO2
Electronegativity

Difference in EN smaller than ionics and is
usually < 1.7

Ex:
HCl
H = 2.2
Cl = 3.2
Difference = 1.0
Bond Polarity

Polar Bond: there is a
difference in EN values
(unequal sharing)

Ex: H
EN=2.2
Cl
EN=3.2

NonPolar Bond: no
difference in EN values.
(equal sharing)
Ex: O2, N2, Cl2, H2
(all the diatomics!)
Comparing Bond Types
Single, Double, Triple Bonds

Atoms can
share single
double or triple
bonds between
them.

Each bond
represents a
shared pair of
electrons.

http://youtu.be/1wpDicW_MQQ
Molecular Formulas

Covalent compounds are molecules.


Made up of all nonmetals.
Molecular formulas: show actual number of
atoms of each element present in compound
Ex:
H 2O
2 hydrogen atoms and 1 oxygen
Structural Formulas

Show how the atoms are bonded together
in a covalent molecule.

Use “lines” to show covalent bonds
Empirical Formulas

Show simplest whole number ratio of atoms
or ions in the compound.
Ex:

MgCl2
1 : 2 ion ratio
Ionic compounds are “salts” or ionic crystals.

All ionic compounds have empirical formulas
You can simplify some molecular
formulas to make them empirical ratios
Ex:
C6H12O6
Simplest ratio of atoms CH2O
Naming Covalent Compounds
Prefix system indicates number of atoms of each element

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Mono
Di
Tri
Tetra
Penta
Hexa
Hepta
Octa
Nona
Deca
Molecule vs. Ionic Crystal
CH4 = 5 atoms in molecule
Formula Units vs. Molecules 7 minutes
https://www.youtube.com/watch?v=dHWqJeSs8ms
NaCl = 1:1 ion ratio
Types of Chemical Formulas Tutorial
 https://www.youtube.com/watch?v=Y2eHJrZI
t0k

Naming Tutorial (Ionic & Covalent)
 https://www.youtube.com/watch?v=9XUsOLa
z3zY

Writing Formulas Tutorial (Ionic & Covalent)
 https://www.youtube.com/watch?v=16agvZ8
K2eM

Drawing Covalent
Molecules
Lewis Structures
See page 10 in Bonding Packet
1.
2.
3.
4.
Count total valence e- in the molecule
Draw molecule with single bonds between
atoms (then subtract these e- from total)
Evenly distribute remaining e- in pairs to
all atoms in molecule that still need eCheck to see if all obey octet rule
(Remember Hydrogen is fine with 2 e- )
5.
If deficient, shift over free e- pairs to make
double or triple bonds as needed.

Draw NH3

Draw H2O

Draw CH4
Crash Course Chemistry:
Lewis Structures: (11 minutes)
http://www.youtube.com/watch
?v=a8LF7JEb0IA
Drawing Polyatomic Ions

Covalently bonded atoms with a group charge
Follow same steps for drawing covalents.
Add or subtract electrons from total valence
depending on charge.
Draw brackets around ion and indicate charge.

Ex: (SO4) -2



6 + 4(6) + 2 = 32 electrons
VSEPR and Molecular Shape

To predict molecular shape, assume valence
electrons repel each other.

Molecule adopts 3D geometry that minimizes
this repulsion.

Valence Shell Electron Pair Repulsion
(VSEPR) theory.
Predicting Molecular
Geometries




Draw Lewis structure
Count total number of electron pairs around
the central atom (both shared and unshared)
Arrange electron pairs to minimize e-repulsion
Multiple bounds count as one bonding pair
Molecular Shapes

Regents Shapes to Know:
Tetrahedral
 Pyramidal
 Bent
 Linear

Is a Molecule Polar?

If the centers of negative and positive
charge do not coincide, then the
molecule is polar.
Look for Symmetry

Polar Molecules:

Have polar bonds and are not symmetrical
 Positive


& negative “partial charges” don’t overlap
They have a “dipole moment”
Nonpolar Molecules

Have nonpolar bonds
OR

Have polar bonds and are symmetrical
 Centers
of positive & negative charge overlap
Example:
In CO2, the polarity of each C-O bond is cancelled
because the molecule is linear.
In H2O, the polar H-O bonds do not cancel because
the molecule is bent.

Tetrahedral

Has 4 atoms bonded
(no free pairs)
Symmetry?
Depends on
what atoms
are attached.
Can be polar
(asymmetrical)
or nonpolar
(symmetrical)

Pyramidal

Three atoms bonded (one free pair)
Symmetry?
All pyramids are asymmetrical.
 These molecules are always POLAR!


Bent
 Two atoms attached (2 free pair)
The 2 free pair make it bent and not linear.
These are
always
asymmetrical
so are always
polar.
H2O
Hey, Water is Polar!!!!!
Never forget this!!!
Without polar water NO LIFE!!

The polar nature of water molecules
allows them to bond to each other in
groups and is associated with the
high surface tension of water.

The polar nature of the water molecule
has many implications. It causes water
vapor at sufficient vapor pressure to
depart from the ideal gas law because of
dipole-dipole attractions. This can lead to
condensation and phenomena like cloud
formation, fog, the dewpoint, etc.

It also has a great deal to do with the
function of water as the solvent of life in
biological systems

Linear
2 atoms in molecule
 Ex:
Cl
Cl (nonpolar bond, sym., nonpolar molecule)

H
Br
(polar bond, asym., polar molecule)
3 atoms in molecule
 Ex: CO2

GOOD FOR REVIEW


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Crash Course Chemistry: Polarity of Molecules
http://www.youtube.com/watch?v=PVL24HAesnc
Dipole Moment:
https://www.khanacademy.org/science/organicchemistry/gen-chem-review/electronegativitypolarity/v/dipole-moment
Properties of Covalent
Compounds
Melting Point
Lower than Ionics
 To melt, you are only separating the weak
bonds between molecules (not within).

Melting Point

Polar Molecules (dipoles/”mini-magnets”):

Have higher melting points than non-polars
because they are harder to separate.
Solubility

Polar Molecules dissolve in
polar solvents as they are
attracted to them


like H2O, CHCl3, NH3 etc.
Non-polar Molecules
dissolve in non-polar solvents

like hexane, CCl4
“Like Dissolves Like”
Oil and water
don’t mix!

How does soap work?
Conductivity

Covalent Molecules do not conduct well as
they do not form ions.


They are “nonelectrolytes”
Except Acids!!!!
 Acids are covalently bonded but in water (aqueous)
they will ionize and conduct current.
 (Acids are not on this test)
Decompose

If the heat gets high enough
covalent compounds will
break down and decompose.

(Remember the lab, sugar
melted first, then it burned and
turned into black carbon)
Other Types of Covalent
Bonds
Coordinate Covalent Bonding
Covalent bond in which one of the
bonding atoms donates both of the
electrons to the bond.
 The other atom donates nothing.

Ex: Forming Hydronium Ion

To form this type of
bond you must have:

A molecule with a free
pair of electrons

Something that needs
to gain 2 electrons
H+1
Ex: Forming Ammonium Ion
Network Solids
Giant network of covalently bonded atoms.
 Large macromolecules
 Extremely strong structures

Unusually high M.P.
 Do not dissolve

Diamonds are a
giant network of
carbon atoms.
Ex: C (s) (graphite, diamond, buckyball),
SiO2 (quartz), GeO2
“Buckyball”
Bonding in Pure Metals
Metallic Bonding

Happens in pure metals or alloys.


Ex:
Mg, Fe, Brass, Au, Ni, Cu
“Delocalized” valence electrons move
about between all the metal atoms.
http://www.youtube.c
om/watch?v=XHV9L
zCH2KA
Metallic Bonding
Properties
 Conducts heat and electricity very well
Conducts as a solid too!

Does not dissolve in solvents

Malleable and Ductile
Properties 2:00:
http://www.youtube.co
m/watch?v=srxNJ03W_
qM

Relatively high melting point.
 Higher MP than covalents.
 Similar MP to most ionics
What is a metal? 4:30
https://www.youtube.co
m/watch?v=Xto88gMm
Dzw
Metallic Bonding

http://www.drkstreet.com/resources/metallic-bondinganimation.swf
EXTRA VIDEO LINKS FOR
FUN AND LEARNING
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Ionic vs. Covalent Bonding
http://youtu.be/QqjcCvzWwww
http://youtu.be/yjge1WdCFPs
Electronegativity
http://youtu.be/Kj3o0XvhVqQ
Bonding Dance Party
http://www.youtube.com/watch?v=w
BCmt_pJTRA
It’s a chemical bond baby”
http://youtu.be/wWUYHHo-zB0
Dancin Queen (Ionic/Covalent
Bonds)
http://youtu.be/BCYrNU-7SfA
Isn’t it Ionic
http://youtu.be/rwRtfrgJL5E