Chapter 8 Sec. 1-3: Covalent Bonding and Lewis Dot Structures NOTES
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Chemical Bonds
o Intramolecular force that holds 2 atoms together
o 3 Types of Chemical Bonds:
 (1) Ionic
 (2) Metallic
 (3) Covalent – nonpolar and polar
o GOAL OF BONDING:
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Sec. 1 The Covalent Bond
o Form molecules (neutral group of atoms held together by covalent bonds)
 Molecular compound – compound whose smallest unit is a molecule
 Ways to represent a molecular compound:
 (1) Chemical formula – indicates the relative # of atoms of each kind in a compound
 (2) Molecular formula – chemical formula of a molecule
o Ex) H2O – water
 (3) Structural formula – uses letter symbols and bonds to show relative positions of
atoms
o Easy to get structural formulas by drawing Lewis dot structures
o Covalent Bond:
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Examples of covalently bonded molecules: Cl2 (chlorine), O2 (oxygen), N2 (nitrogen), H2O (water),
CO2 (carbon dioxide), CH4 (methane)
Single Covalent Bonds
o ________________________________ pair of electrons is shared
o Single covalent bonds are also called sigma bonds (σ)
o Example of single bonded molecule: H2
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Double Covalent Bonds
o ________________________________ pairs of electrons are shared
o Consist of one sigma and one pi bond
 Pi bond (π) – forms when parallel orbitals overlap and share electrons below and above where
the two atoms are joined together
 Drawing of a sigma and pi bond:
o
Example of double bonded molecule: O2
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Triple Covalent Bonds
o __________________________________ pairs of electrons are shared
o Consist of one sigma and two pi bonds
o Example of triple bonded molecule: N2
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Strength of Covalent Bonds
o Bond Length:
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o
Bond Length Trends
 (1) The shorter the bond length, the _______________________________ the bond
 (2) Triple bonds are shorter and stronger than double bonds and double bonds are
shorter and stronger than single bonds
Bond-dissociation Energy (Bond Energy):
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Bond Energy Trends:
 (1) The smaller the bond length, the stronger the bond, and the greater the bond energy
 (2) A triple bond is the shortest, is the most difficult to break, and has the highest bond
energy.
 (3) A single bond is the longest, is the easiest to break, and has the lowest bond energy.
The sum of the bond-dissociation energy values for all of the bonds in a molecule is the amount
of chemical potential energy in a molecule of that compound
Total energy change of a chemical reaction is determined from the energy of the ____________
broken and formed
 Must ____________________ energy to _____________________ bonds – endothermic
 Must ____________________ energy to _____________________ bonds – exothermic
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Endothermic reaction
o Greater amount of energy is required to break the existing bonds in the
reactants than is released when the new bonds form in the products
Exothermic reaction
o More energy is released during product bond formation than is required to
break bonds in the reactants
Sec. 3 Molecular Structures
o Electron-dot Structures: show valence electrons of atoms
 Valence Electrons:
 Determine chemical properties of element
 Involved in chemical bonding
 Electrons in outermost energy level (s & p orbitals)
 DRAW THE ELECTRON DOT STRUCTURES FOR NITROGEN AND FLUORINE BELOW:
o
o
Lewis Dot Structures: show arrangement of electrons in a molecule
 Steps to drawing a Lewis Dot Structure:
 (1) Calculate total # of valence electrons
o Ex) CO2 = 4 + 2(6) = 16 valence electrons
 (2) Determine central atom
o Usually listed first or is the least electronegative (furthest to the left on the
periodic table)
 (3) Draw skeletal structure
 (4) Connect every bonded pair of atoms by a dash (represents 2 electrons)
 (5) Distribute remaining electrons to atoms surrounding the central atom to satisfy the
Octet Rule
 (6) Distribute remaining electrons to central atom (may require multiple bonds)
Know that there are a few EXCEPTIONS to the octet rule:
 Suboctets
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o
Expanded octets
Lewis Dot Structure Practice Problems
 (Example #1) Draw the Lewis Dot Structure for ammonia.
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(Example #2) Draw the Lewis Dot Structure for ammonium.
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(Example #3) Draw the Lewis Dot Structure for hydrocyanic acid.
Resonance Structures
 Possible to have more than one correct Lewis dot structure
 Show all Lewis dot structure possibilities for a molecule by drawing resonance structures
 Resonance – occurs when more than one valid Lewis dot structure can be written for a molecule
or ion
 Examples of Resonance Structures:
IONIC VS. MOLECULAR COMPOUNDS
o Forces in ionic compounds are very strong.
o Forces in molecular (covalent) compounds are strong, but forces between molecules are weak.
Characteristic
Hardness
Melting Point (MP)
Boiling Point (BP)
Solubility
Conductivity
Bond Formed
Examples
Ionic Compounds
Molecular (Covalent)
Compounds