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Ch. 12 Notes---Covalent BondsCovalent Bonds
• ____________ electrons between two atoms in order to fill the outer energy level (or shell)
• Each bond involves the sharing of _____ _________ of electrons.
Single Bonds= __ e-’s Double Bonds= __ e-’s Triple Bonds=__ e-’s
Sharing
one pair
2 4 6
Sharing is Caring!!
Caring is Covalent!!!
Sharing
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.
a) H2 H · + · H H:H
b) F2 :F· + ·F: :F:F:
c) N2 :N · + ·N: :N :: N: (triple bond)
d) NH3 H:N:H
..
......
.. ..
.. ..
·
·
·
·
· ·
..
..H
Ways to Represent Covalent Bonds in Compounds
(3) “Lines” for bonds.
a) H2
b) F2
c) N2
d) NH3
e) H2O
.. ..
.. ..
׀H
׀H
..
H–H
:F–F:
:N≡N:
H–N–H
H–O:
Octet Rule
• Atoms want ___ e-’s in their outer shell when forming compounds.
• This will mean ___ dots around them all together. This is the stable e- configuration of a __________ _______!
• Important exception: Hydrogen = only needs __ to be full (like He).
• Other Exceptions:
PCl5 (___ e-) SF6 (___ e-) BF3(___e-)
8
8 noble gas
2
10 12 6
The 7 Diatomic Elements
• Some elements will covalently bond to themselves to form a molecule composed of ____ atoms.
• These elements are never found in nature as single atoms. Instead, they will be bonded as a ________ when they are in the “_________________” state.
• The 7 diatomic elements are the gases H, O, N, and all of the _________________, (Group 7A).
H2, O2, N2, Cl2, Br2, I2, F2
“HONClBrIF”
two
elementalpair
halogens
Air contains N2 and O2 molecules.
The decomposition of two water molecules
Resonance
• Resonance is the ability to draw 2 or more different e- dot notations that obey the octet rule.
Examples: O3 (ozone) and SO2
Practice Problem: Draw the resonance structures for CO3-2.
VSEPR Theory: Molecular Shapes
• Most shapes are based on a __________________.
Examples: CH4 CCl4
• Removing the top of the tetrahedral makes the ________________ shape.
Examples: NH3 PCl3
tetrahedral
pyramidal
VSEPR Theory: Molecular Shapes
• Removing one side of the pyramid makes the _____________ shape.
Examples: H2O H2S
• If there are only two atoms bonded, it is ______________.
Examples: O2 HCl CO2 (linear because of its double bonds.)
bent
linear
VSEPR Theory: Molecular Shapes
• The last shape we will need to know is called “trigonal planar”. “Trigonal” means that the central atom is bonded to ___ other atoms. “Planar” means that the 3 atoms all lie in the same ______________.
Example: BF3
• (Notice that Boron will only have ___ e-’s around it. The missing pair of electrons will make it planar instead of ________________.)
3plane
6pyramidal
Figure 12.4 The three possible
types of bonds.nonpolar
polar
ionic
Polar and Nonpolar Bonds
• Even though the electrons in a covalent bond are shared, sometimes the attraction for the bonded pair, (the _____________________), is uneven. This gives rise to 3 bond types.
• nonpolar covalent bonds: ____________ sharing of the e- pair
• polar covalent bonds: ________________ sharing of the e- pair
• ionic bonds: a ___________ of e-’s from the metal to the nonmetal
This last type of bond will be discussed in detail in Chapter 15.
How To Determine the Bond Type
• Bond type is based on the electronegativity _____________ between the two bonded atoms.
(See p.402 for electronegativity values.)
electronegativity
equal
unequal
transfer
difference
How To Determine the Bond Type
0 to 0.4 = ______________ covalent bond
0.5 to 2.0 = _____________ covalent bond
Above 2.0 = _______________ bond
•Practice Problems: Determine the type of bond that forms between the atoms in the following compounds.
a) CO2 b) NaCl c) CH4
nonpolar
polar
ionic
2.5 3.5 0.9 3.0 2.5 2.1
1.0 = polar covalent 2.1 = ionic 0.4 = nonpolar covalent
Polarity of Molecules
• One side is slightly (__) and the other side is slightly (__).
• Polar molecules are also known as _______________.
• Polarity depends on the __________ and symmetry of the molecule.
• symmetrical molecules (looks the same on all sides)= ___________
• asymmetrical molecules = ___________
• Polar molecules are moved by ____________ charges. (DEMO!)
+ –
dipole
shape
nonpolar
polar
static
Molecular Polarity
Practice Problems: Determine if the following molecules are polar or nonpolar based on their shape.
a) CH4 b) NH3 c) H2O d) HCl e) CO2
Dipole of NH3
symmetrical tetrahedral
asymmetrical pyramidal
asymmetrical bent
asymmetrical linear
symmetrical linear
nonpolar nonpolarpolar polar polar
Bond Dissociation Energy
• This is the energy needed to ___________ the bond.
• Generally, the longer the bond, the _____ energy it takes to break it.
• Single bonds take ________ energy to break than double bonds and triple bonds require the _________ energy to break.
• When bonds form, energy is _____________.
(Breaking bonds requires the addition of energy.)
released
less
lessmost
break
Intermolecular Attractions
• The __________ attractions between one molecule and another are called _______ ______ ________ forces.
• They cause gas particles to stick together and _______________ at low temperatures.
weak Van der Waals
condense
Dispersion Forces
There are two types of intermolecular forces:
(1) ____________________ forces: (the weaker type)
– caused by random _______________ motion
– generally _____________ with ________ electrons in the molecule
Dispersion
electronstronger more
− 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) ____________ interactions: (the stronger force)
– caused by the attraction of the (__) side of one polar molecule and the (__) side of a different polar molecule
Dipole-Dipole
+–
Hydrogen Bonds
• “________________ Bonds” are a special type of dipole interaction.
• They occur between the hydrogen of one polar molecule and the ____, ___ or ___ of another polar molecule.
Hydrogen Bonding in Water
Hydrogen
N O F
Hydrogen Bonds
• The ladder rungs in a DNA molecule are hydrogen bonds between the base pairs, (AT and GC).
Hydrogen Bonds in
DNA
Naming Molecular Compounds
• You do not use the ion sheet for molecules because no __________ are needed. They ______________ electrons instead of transferring them.
• Use ________________ to indicate the # and kind of atom in the compound.
mono=1 di=2 tri=3 tetra=4 penta=5 hexa=6 hepta=7 octa=8 non=9 deca=10
• Use the general format shown below…
prefix-(except mono)-name the 1st element prefix-name the 2nd element ending with -ide
Practice Problems: Name the following molecules.
N2O5 CO Cl4F7 SO3
chargesshare
prefixes
dinitrogen pentoxide
carbon monoxide
tetrachlorine heptafluoride
sulfur trioxide
Writing Molecular Formulas
• The prefixes in the name tell you the # of atoms of each element there are. (Those become the _________________ in the formula!)
Practice Problems: Write the formula for each molecule.
nitrogen monoxide carbon tetrachloride diphosphorous pentoxide
subscripts
NO CCl4 P2O5