Ch. 12 Notes---Covalent Bonds
Covalent Bonds
Sharing electrons between two atoms in order to fill the outer
• ____________
energy level (or shell)
one _________
pair
• Each bond involves the sharing of _____
of electrons.
2 e-’s Double Bonds= __
4 e-’s Triple Bonds=__
6 e-’s
Single Bonds= __
Sharing
Sharing
is Caring!!
Caring is Covalent!!!
Ways to Represent Covalent Bonds in Compounds
(1) Quantum Mechanical or Bohr Model of the Atom.
Ways to Represent Covalent Bonds in Compounds
(1) Quantum Mechanical or Bohr Model of the Atom.
Ways to Represent Covalent Bonds in Compounds
(2) “Dots” for bonds. (Lewis Structures)
a) H2
H· +
b) F2
..
:F..·
c) N2
·
:N· ·
d) NH3
·H
+
+
..
H:N:H
..
H
 H:H
..
·..F:
·
·N:
·
.. ..
 :F:F:
.. ..
··
 :N::N:
(triple bond)
Ways to Represent Covalent Bonds in Compounds
(3) “Lines” for bonds.
a) H2
H–H
b) F2
.. ..
:F–F:
.. ..
c) N2
:N≡N:
d) NH3
H–N–H
¨
‫׀‬
H
e) H2O
..
H–O:
‫׀‬
H
Carbon’s Hybrid Orbital
↑↓
C …___
↑
___
↑
___
2s
C …___
↑↓
___
(Before)
___
↑
(After: 4 covalent bonds available)
2p
___
↑
___
↑
2sp3
Practice Problem: Draw CH4 using arrows, dots, and lines for bonds.
↑
C …___
↑
___
↑
___
↑
___
2sp3
↑ H ___
↑
H ___
1s
1s
↑
H ___
1s
H ___
↑
1s
The 7 Diatomic Elements
• Some elements will covalently bond to themselves to form a
molecule composed of ____
two atoms.
• These elements are never found in nature as single atoms.
Instead,
they will be bonded as a ________
pair when they are in the
“_________________”
state.
elemental
• The 7 diatomic elements are the gases H, O, N,
_________________,
(Group 7A).
halogens
H2, O2, N2, Cl2, Br2, I2, F2
“HONClBrIF”
and all of the
Air contains N2 and O2 molecules.
The decomposition of two water molecules
Octet Rule
8 e-’s in their outer shell when forming compounds.
• Atoms want ___
• This will mean ___
8 dots around them all together. This is the stable
noble
gas
e- configuration of a __________
_______!
2 to be full (like He).
• Important exception: Hydrogen = only needs __
• Other Exceptions:
PCl5 (___
10 e-)
SF6 (___
12 e-)
BF3(___e
6 -)
VSEPR Theory: Molecular Shapes
• Most shapes are based on a __________________.
tetrahedral
Examples: CH4
CCl4
• Removing the top of the tetrahedral makes the ________________
pyramidal
shape.
Examples: NH3
PCl3
VSEPR Theory: Molecular Shapes
• Removing one side of the pyramid makes the _____________
bent
shape.
Examples: H2O
H2S
• If there are only two atoms bonded, it is ______________.
linear
Examples: O2 HCl CO2 (linear because of its double bonds.)
VSEPR Theory: Molecular Shapes
•Another we will need to know is called “trigonal planar”.
“Trigonal”
means that the central atom is bonded to ___
3 other atoms. “Planar”
plane
means that the 3 atoms all lie in the same ______________.
Example:
BF3
• (Notice that Boron will only have ___
6 e-’s around it.
The missing
pyramidal
pair of electrons will make it planar instead of ________________.)
Polar and Nonpolar Bonds
• Even though the electrons in a covalent bond are shared, sometimes
the attraction for the bonded pair, (the _____________________),
is
electronegativity
uneven. This gives rise to 3 bond types.
• nonpolar covalent bonds: ____________
sharing of the e- pair
equal
• polar covalent bonds: ________________
unequal
sharing of the e- pair
transfer of e-’s from the metal to the nonmetal
• ionic bonds: a ___________
How To Determine the Bond Type
difference
• Bond type is based on the electronegativity _____________
between
the two bonded atoms.
Figure 12.4
The three possible
types of bonds.
nonpolar
polar
ionic
Figure 12.4: Electronegativity values for selected
elements.
How To Determine the Bond Type
nonpolar
0 to 0.4 = ______________
covalent bond
polar
0.5 to 2.0 = _____________
covalent bond
ionic
Above 2.0 = _______________
bond
•Practice Problems:
Determine the type of bond that forms between
the atoms in the following compounds.
2.5 3.5
0.9 3.0
a) CO2
b) NaCl
1.0 = polar covalent
2.1 = ionic
2.5 2.1
c) CH4
0.4 = nonpolar covalent
Polarity of Molecules
• One side is slightly (__)
+ and the other side is slightly (__).
–
dipole
• Polar molecules are also known as _______________.
shape
• Polarity depends on the __________
and symmetry of the molecule.
• symmetrical molecules (looks the same on all sides)= ___________
nonpolar
• asymmetrical molecules = ___________
polar
• Polar molecules are moved by ____________
static
charges.
(DEMO!)
Molecular Polarity
Practice Problems: Determine if the following molecules are polar or
nonpolar based on their shape.
a) CH4
b) NH3
symmetrical
tetrahedral
asymmetrical
pyramid
nonpolar
polar
c) H2O
d) HCl
e) BF3
asymmetrical
bent
asymmetrical
linear
symmetrical
trigonal planar
polar
polar
nonpolar
Dipole of NH3
Dipole of H2O
Bond Dissociation Energy
• This is the energy needed to ___________
break
the bond.
• Generally, the longer the bond, the _____
less energy it takes to break it.
• Single bonds take ________
less energy to break than double bonds and
most energy to break.
triple bonds require the _________
released
• When bonds form, energy is _____________.
(Breaking bonds requires the addition of energy.)
Bond Dissociation Energy
Intermolecular Attractions
• The __________
weak
attractions between one molecule and another are
called _______
______
________ forces.
Van
der Waals
• They cause gas particles to stick together and _______________
at
condense
low temperatures.
Dispersion Forces
There are two types of intermolecular forces:
Dispersion
(1) ____________________
forces: (the weaker type)
– caused by random _______________
motion
electron
stronger
more electrons in the
– generally _____________
with ________
molecule
− exist between all
types of molecules
− This force causes
Br2 to be a liquid
and I2 to be a solid
at room temperature.
Dipole Interaction Forces
(2) ____________
Dipole
interactions: (the stronger force)
+ side of one polar molecule
– caused by the attraction of the (__)
and the (__)
– side of a different polar molecule
Hydrogen Bonds
•________________
Hydrogen
“Bonds” are a special type of dipole interaction.
• This attraction between molecules is not a chemical bond. Electrons
are not being shared or transferred.
•They occur between the hydrogen of one polar molecule and the
____,
N ___
O or ___
F of another polar molecule.
Hydrogen
Bonding
in Water
Hydrogen Bonds
• The ladder rungs in a DNA molecule are hydrogen bonds between
the base pairs, (AT and GC).
Hydrogen
Bonds in
DNA
Intermolecular Forces At Work
•Substances that contain stong intermolecular forces have a ________
higher
melting point and a _________
higher boiling point.
• Liqids containing strong intermolecular forces have higher surface
tension and a higher viscosity.
Surface Tension
Ionic Bonding & Ionic Compounds
Ionic Bonds
•
•
metals transfer their _____________
valence
Form when ___________
electrons
to a _______________.
nonmetal
cation
The forces of attraction between the ____________
(+) and the
_____________
anion
(-) bind the compound together.
How to Represent an Ionic Bond
(1) Electron Configuration:
Na 1s2 2s2 2p6 3s1
Na… ___
↑
3s
Cl 1s2 2s2 2p6 3s2 3p5
↑ ↓ ___
↑ ↓ ___
Cl… ___
↑ ↓ ___
↓
3s
3p
How to Represent an Ionic Bond
2) Bohr Model
Lithium
Fluorine
How to Represent an Ionic Bond
3) Electron Dot Notations:
Na +
Cl
 [ Na+1] [ Cl -1]
Practice Problems: (1) Draw the electron dot notation for the
formation of an ionic compound between sodium and oxygen.
(2) Draw the electron configuration notation for the formation of an
ionic compound between magnesium and fluorine.
Practice Problems:
3)
a) Draw the electron dot notation for a potassium atom.
K
b) Draw the electron dot notation for a potassium ion.
[K+1]
(4)
a) Draw the electron dot notation for a sulfur atom.
S
b) Draw the electron dot notation for a sulfur ion.
[S
-2]
Properties of Ionic Compounds and Covalent Molecules
Ionic:
•
•
•
•
•
Conductors
_______________
of electricity when dissolved water or melted.
formed between __________
metals and _________________
nonmetals
high melting points
have _________
usually ________
very soluble in water
ionic crystalline
form ___________________
solids
(dissolved salt)
Crystalline Patterns
Pyrite
• mineral form of the iron disulfide (FeS2)
with a gold-like appearance, making it
also known as "fool's gold"
Gypsum
• Gypsum is a very soft mineral
composed of calcium sulfate dihydrate,
with the chemical formula CaSO4·2H2O.
Properties of Ionic Compounds and Covalent Molecules
Molecular:
• ________________
of electricity
Insulators
nonmetals
• formed between two _______________
low melting points
• usually have ________
• solubility in water _______:
(polar =dissolve; nonpolar = insoluble)
varies
covalent crystalline
•forms ______________________solids.
For a compound to to conduct electricity it must have:
ions
(1) Charged Particles (________)
(2) Particles Free to Move (___________
or __________
liquid
aqueous phase)
Quartz
• Quartz is the common mineral form of
silicon dioxide (SiO2). It is the dominant
mineral in most sands and sandstones.
Demonstration
great
conductor
poor
conductor
good
conductor
Pure
H2O
nonconductor