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Ch. 16 Covalent Bonding
VSEPR Theory, Polarity, and using Electronegativity
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Covalent Bonds– Forms when 2 atoms share a pair of valence e-
A. Types of Covalent Bonds1. Single Covalent Bond – two atoms share one pair of electrons
Ex: F2
F F● ●
●●
●●
● ●●●●
●● ●F F● ●
●●
●●
● ●●●●
●● ●or F F
● ●●●
●
●●●●
●● ●
Unshared pair – e- not shared between atoms
What makes this bonding work?Atoms have 8 e- in their outer level to make them stable
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Ex: H2
H● H● H ● H● or H H
Why does H2 only need 2 e- to be stable?first energy level only contains 2 e-
Covalent Bonds (cont.)
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Covalent Bonds (cont.)
2. Double Covalent Bond – 2 pairs of electrons are shared between atomsEx: O2
O●●
●●●
●●O
●●●●●
●O● ●
● O or●●●
● ● ●
● ●O● ● O
● ●
● ●●
●
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Covalent Bonds (cont.)
3. Triple Covalent Bond – 3 pairs of electrons are shared between atomsEx: N2
NN●●
●●
●N●●
●●
●N●
● N●● or N●
●●●● ●● ●● ●
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Covalent Lewis Dot Structures
1. Determine the # of valence e- in each atom in the molecule
(# valence e- = roman numeral for group A atoms)
2. The central atom is often the first atom written & is usually the atom with the least # of e-. (Exception – H can’t be the central atom). This is going to be the atom that needs to share the most electrons.
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Lewis Dot Structures for Compounds
3. Place the electrons around the atoms so each is stable (8 around it, except H – only 2)
Examples:1. Br2
Br● ●
● ●●
●
●Br● ●
●●
●
●
●Br● ●
●●
●
●Br● ●
●
●●
●
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2. NH3
N●
● ●
●
●
H●
H●
H●
N● ●
HH
H
3. CO2
C●
●
●
●
O
O● ●
● ●●●
●●●
●
●●
CO O● ●
●●
● ●
●●
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4. CCl4
C ●
●
●
Cl●
Cl●
Cl●C ClCl
Cl
5. H2O
H●
O● ●●
●●
●
●
Cl
● ●
● ●● ●
● ●
● ●● ●
● ●
●●
●●
●●
●●●
● ●
Cl● ●
● ●● ●
●●
● ●
● ●
●●
● ●
●●
●●
●●
●●
H●
O
H
H● ● ●
●
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Covalent Bond Practice Problems:
1. CH4 4. OF2
2. H2 5. CHI3
3. PH3 6. CO2
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VSEPR Theory
• Explains the shapes of molecules. • The VSEPR theory states: b/c electrons repel each
other, molecules adjust their shapes so that the valence e- pairs are as far apart from each other as possible.
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Shape Formula Bond Angle ElectronsLinear AX2 180o 4 shared
0 unshared
Linear AX 180o 1 shared3 unshared
Bent AX2 105o 2 shared2 unshared
Trigonal Pyramidal
AX3 107o 3 shared1 unshared
Tetrahedral AX4 109.5o 4 shared0 unshared
Trigonal Planar AX3 120o 4 shared0 unshared
Contains a double bond
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Bond Polarity
Polar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are not shared equally
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Nonpolar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are shared equally
Bond Polarity (cont.)
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Differences between polar, nonpolar, and ionic bonds
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How do you determine if a bond is polar, nonpolar, or ionic?
Subtract the electronegativities of the bonding atoms (p. 405 in textbook)
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Electronegativity Differences & Bond Type
Type of BondElectronegativity Difference Range
Nonpolar Covalent Bond 0.0 – 0.4
Polar Covalent Bond 0.5 – 2.0
Ionic Bond greater than 2.0
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Tell if the bonds between the following atoms are polar, nonpolar, or ionic:
H 2.1C 2.5 0.4 Nonpolar
1. Hydrogen and Carbon
2. Oxygen and Carbon
3. Potassium and Chlorine
4. Fluorine and Fluorine
5. Nitrogen and Oxygen
O 3.5C 2.5 1.0 Polar
K 0.8Cl 3.0 2.2 Ionic
F 4.0F 4.0 0.0 NonpolarN 3.0O 3.5 0.5 Polar
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Polar Molecule – a molecule with a positive and negative end. Polar bonds must be present.
Polarity of Molecule
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Polarity of Molecule (cont.)
It is possible to have polar bonds but not a polar molecule!• Carbon dioxide has 2 polar bonds and is linear.• Bond polarities cancel out b/c they are in opposite directions.
CarbonOxygen Oxygen
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Practice:
Write the dot structure of the following molecules – then predict the shape and polarity
1. I2
2. PCl3
3. H2S
4. CHI3
5. SiO2
6. CH2O