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Covalent Bonding
Covalent Bonding Molecule: neutral group of atoms that are
held together by covalent bonds Covalent Bond: sharing of electrons
between two atoms, “owned” by the two bonded atoms. Occurs most commonly between nonmetal
elements
Covalent bonding: Fluorine
F F
Fluorine has seven valence electrons A second Fluorine atom also has seven
By sharing electrons…Both atoms end up with full orbitals (stable octets)
8 Valence electrons
8 Valence electrons
Covalent Bonding: Oxygen
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n = 1
O1s22s22s22p4
n = 2
+
O2
Atoms share electrons to achieve a stable octet (8 electrons in valence shell).
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Octet Rule
The Octet Rule applies to covalent bonds: atoms bond to achieve 8 valence electrons Exceptions:
Hydrogen is satisfied with 2 valence electrons
Beryllium is content with 4 valence electrons
Boron is satisfied with 6 valence electrons
Bond Strength The strength of a bond is determined by how
many electrons are shared between two atoms.
Single Bond - Atoms share one PAIR of electrons (2 e-) Weakest bond, most flexible
Double Bond – Atoms share TWO pairs (4 e-)of electrons
Triple Bond – Atoms share THREE pairs (6 e-)of electrons Strongest bond, most rigid
(Pg. 182)Relationship between Bond Length and Bond Energies
Bond Energy = Energy required to break a chemical bond Unit: kJ High bond energy = High bond strength
Plot Bond length on the x-axis, Plot bond energy on the y-axis
Result: Bond length decreases as the strength of the bond _____________. Answer: Increases
Covalent Bonds: Lewis Structures Lewis Structure: It shows the molecular arrangement of covalent molecules, using the electron-dot notation. Lone Pair electrons = Unpaired electrons
Q: Do we use lewis structures to illustrate ionic bonds?
Cx
xx
x
x x
F
x x
x
x x
F x
x
xx
x F x
x
xx
x x
F x
x
How To: Lewis Structures (Ex: CH3I)Step 1. Determine the type and number of atoms in
the molecule.Step 2. Determine the total number of valence
electrons available in the molecule.Step 3. Arrange the atoms.
Q: Which atom is central? *(next slide)Step 4. Start by putting two electrons between
atoms for each covalent bond. Then place electrons around each atom to fulfill the Octet Rule
Step 5. Count the electrons to check your work. Ask yourself, does it equal the number of electrons in step 2?
How to: Lewis StructuresQ: Which atom is central? A: If carbon is present, it is the central atom.
Hydrogen is never the central atom. Otherwise, the central atom is the least-electronegative atom.
Q: What does “electronegative” mean?A: Electronegativity: The ability of an atom to
attract electrons in a chemical compound. If an atom is highly electronegative, it is the more “dominant” atom and “hogs the electrons.”
Lewis Structure
o
Co
o o
x
Ho
Co
o oH x
x
H
xH
x H CH
H
H
H
x
xxx
x x
I x
o
No
o o
o o
No
o ox
xxx
x x
I x
x x
xx
x x
I x
xxx
x x I
x
x
o o
Nx
xxx
x x
I
x xx
x x
I x
xx
x x I
x
x
o
o
Co
o o x
xxx
xO x
x
xxx
xO x
x
xxx
xO x
o
Co
o o O = C = O
x x
x x x x
x x
methane (CH4)
carbon dioxide (CO2)
nitrogen triiodide (NI3)
Lewis Structures: Practice
Ammonia, NH3
Hydrogen Sulfide, H2S Silane, SiH4
Phosphorus Trifluoride, PF3
Naming Covalent Molecules
Greek prefixes are used to indicate how many atoms of each element are present in the molecule.
P4O10Prefix needed if first element contributes more than one atom
Root Name of 2nd element + ide
Prefix indicating number of atoms
Name of first element
+ +
tetraphosphorus decoxide
Naming Covalent MoleculesNumb
erPrefix
1 Mono-2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octo-9 Nona-
10 Deca-
The “o” or “a” at the end of a prefix is usually dropped when another vowel follows it. “monooxide”
becomes “monoxide” “pentaoxide”
becomes “pentoxide”
Examples…Name the following - SO3: Sulfur ______?________
Answer: Sulfur trioxide PBr5: _____?_____ _______?________
Answer: Phosphorus pentabromide As2O5: ______?_____ Pentoxide
Answer: Diarsenic Pentoxide
Examples… Write the chemical formulas - Carbon tetriodide
Answer: CI4
Dinitrogen trioxide Answer: N2O3
Silicon dioxide Answer: SiO2
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