ch. 16 covalent bonding vsepr theory, polarity, and using electronegativity
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Ch. 16 Covalent Bonding
VSEPR Theory, Polarity, and using Electronegativity
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
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.)
Covalent Bonds (cont.)
2. Double Covalent Bond – 2 pairs of electrons are shared between atomsEx: O2
O●●
●●●
●●O
●●●●●
●O● ●
● O or●●●
● ● ●
● ●O● ● O
● ●
● ●●
●
Covalent Bonds (cont.)
3. Triple Covalent Bond – 3 pairs of electrons are shared between atomsEx: N2
NN●●
●●
●N●●
●●
●N●
● N●● or N●
●●●● ●● ●● ●
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.
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● ●
●
●●
●
2. NH3
N●
● ●
●
●
H●
H●
H●
N● ●
HH
H
3. CO2
C●
●
●
●
O
O● ●
● ●●●
●●●
●
●●
CO O● ●
●●
● ●
●●
4. CCl4
C ●
●
●
Cl●
Cl●
Cl●C ClCl
Cl
5. H2O
H●
O● ●●
●●
●
●
Cl
● ●
● ●● ●
● ●
● ●● ●
● ●
●●
●●
●●
●●●
● ●
Cl● ●
● ●● ●
●●
● ●
● ●
●●
● ●
●●
●●
●●
●●
H●
O
H
H● ● ●
●
Covalent Bond Practice Problems:
1. CH4 4. OF2
2. H2 5. CHI3
3. PH3 6. CO2
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.
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
Bond Polarity
Polar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are not shared equally
Nonpolar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are shared equally
Bond Polarity (cont.)
Differences between polar, nonpolar, and ionic bonds
How do you determine if a bond is polar, nonpolar, or ionic?
Subtract the electronegativities of the bonding atoms (p. 405 in textbook)
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
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
Polar Molecule – a molecule with a positive and negative end. Polar bonds must be present.
Polarity of Molecule
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
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