Covalent Bonds Study Guide - Chapter 9
Chemistry - Dr. Hazlett
1
I. Diagrams for Inorganic Molecules
A. Lewis Dot diagrams
1. Monatomics, Diatomics and Polyatomics
2. Term Abbreviations (KNOW THESE)
a. Ve - valence electrons
b. BP - bonding pair of electrons
c. LP - lone pair (unbonded pair) of electrons
d. TA - terminal atom, also called Peripheral or Ligand Atoms
e. FC - formal charge
B. Steps in Diagramming (Summary)
1. Determine compound type
a. Ionic - metal w/ nonmetal
b. Covalent - nonmetal w/ nonmetal
c. Metallic - metal w/ metal
2. Determine Ve and possible BP by dividing by 2
a. Adjust for -/+ charges if ionic compound
3. CA - one w/ lowest χ value
a. Can never be H since can form only one bond
4. Add Ve and BP remembering octect/duplet rule
5. FC = Ve - (n + b/2)
a. Must equal 0 to be correct
6. Simplify w/ lines representing bond numbers
7. If ionic, in brackets w/ charge indicated
II. Covalent Bonds
A. Form when pair(s) of Ve are shared to complete atom’s octects
1. Atoms attempt to attain noble gas configuration [octect/duplet]
2.
Group
IVA
VA
VIA
VIIA
VIIIA
Ve
4
5
6
7
8
# Bonds to Make Octet
VSEPR / Θ
4
Tetrahedral / 109.5
3
Trigonal Planar / 120
2
Linear, Bent / 180, 109.5
1
0
5
Trigonal Bipyramidal / 120, 180
6
Octahedral / 90, 180
a. Bent shape is due to paramagnetism of TAs
3. Single cov. bond also called a sigma bond (σ) since a HO
a. Double cov. bond is 1σ and 1 π bonds; triple is 1 σ and 2 π bonds
Covalent Bonds Study Guide - Chapter 9
Chemistry - Dr. Hazlett
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III. Covalent Properties
A. Comparison w/ Ionics
Ionics
Form crystalline solids – crystal lattice
(salts)
Covalents
Form g, l, and/or s
Exothermic Reactions
Endothermic reactions (mainly)
High melting/boiling points due to strong
Bonds (e- transfer)
Low melt/boil points since atoms
remain somewhat independent
High Do needed to break bonds
Lower Do needed
Conduct thermal/electrical energy (e- can
be transferred or lost)
Poor conduction, insulators - no
“free” e-‘s to leave
Properties due to electrostatic attraction
among atoms
Properties due to IMF bonds
Hard, brittle
Soft, malleable, flammable
Soluble in H2O (like dissolves like)
Nonsoluble in nonpolar solutions
Nonsoluble in nonolar liquids
Soluble in polar liquids like H2O
Metal cation to Nonmetal anion bond
Nonmetal to nonmetal bond
Large difference in χ values
Little/No difference in χ values
IV. Naming Covalent Compounds
A. See previous Study Guides for detailed rules!
B. In general:
1. Name CA first using appropriate prefix and full name
a. This is usually the least abundant atom in molecule
b. Mono is often not used – but is not incorrect is done
2. 2nd word is other atom/polyatomic w/ “ide” attached to its root
a. Again, use appropriate prefix to denote how many
3. Remember – many have common names (LEARN THEM)
4. Halogens and other atoms are naturally diatomic (LEARN THEM)
Covalent Bonds Study Guide - Chapter 9
Chemistry - Dr. Hazlett
V. IMF
A. Inter/Intramolecular Forces
1. KE of molecules
a. Vibration
b. Rotation
c. Translation
2. Intermolecular Force
a. van der Waals/London/Dispersion Forces and Bonds
(1) Dipole-Dipole
(2) Induced Dipole
(3) Induced Dipole – Induced Dipole
b. H Bonds
c. Effects of IMF on molecules
3. Polarity
a. Results from δ+ and δ- charges in a molecule
b. Higher the χ, negative; and lower the χ, positive charges
(1) If χ = 0, then no dipole and nonpolar molecule
(2) ex. Most diatomics are nonpolar
c. Separation of charges creates a dipole (2 poles)
d. Molecular shape and angles (geometry) affect polarity
(1) Dipole moment is sum of all bond dipole charges
(2) Know VSEPR shapes and angles
VII. Molecular Structures
A. Determining shape and angles of molecular bonds (VSEPR shapes)
1. Predicted using Lewis Dot Diagrams
2. Use element symbols, lines for bonds, and dots for Ve
B. Procedures
1. Find the CA and TA
a. H is always a TA, never a CA
b. CA is usually least abundant and/or lowest χ value
2. Find total # of Ve available for bonding (Σ of all Ve)
3. # BP = # Ve divided by 2
4. Place 1 BP between CA and each TA
5. Subtract # of e- pairs used in Step 4 from total # of BP found in Step 5
a. Remaining e- pairs include LP and double/triple bonds
b. Place LP around TA to complete their octets
c. Remining pairs go to CA
6. If CA is not surrounded by 4 pair of e-, no octet. . .
a. Must convert 1 or more LP on TA to double/triple bonds w/ CA
C. Hypervalence or Expanded Octets – remember some atoms (S, P, Xe. etc.) can have
more than 8 valence electrons
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Covalent Bonds Study Guide - Chapter 9
Chemistry - Dr. Hazlett
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1. This creates a weird Lewis Dot Structure – KNOW ABOUT THIS!
D. Resonance Structures – same molecule can be correctly drawn in different shapes
E. Know these diatomics and polyatomics:
1. Halogens, F2, Cl2, Br2, I2 and O2, N2, H2, P4, S8
F. Know EN Chart to determine if covalent or ionic, and non/polar covalent bonds
Electronegativity
Difference
Percent Ionic
Character
Bond
Type
0.2
1%
Non-polar
0.4
4
Covalent
0.5
-------------------------------------------------------------------------0.6
9
0.8
15
1.0
22
Polar
1.2
30
Covalent
1.4
39
-------------------------------------------------------------------------1.6
47
Ionic if metal/nonmetal
1.8
55
Polar Cov. If Non/Nonmetal
2.0
63
-------------------------------------------------------------------------2.2
70
2.4
76
Pure Ionic
2.6
82
2.8
86
3.0
89
3.2
92