1. Chemical Bonding
The Covalent Bond

2. Covalent or Ionic ???
Electronegativity – the attraction that an atom has for the electrons that it is sharing w/ another atom
Scale devised by Nobel Prize winner Linus Pauling
Based on scale with fluorine assigned 4.0, the highest value
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H. Stephen Stoker

3. Forming Chemical Bonds
According to the Lewis model
an atom may lose or gain enough electrons to acquire a filled valence shell and become an ion. An ionic bond is the result of the force of attraction between a cation and an anion.
an atom may share electrons with one or more other atoms to acquire a filled valence shell. A covalent bond is the result of the force of attraction between two atoms that share one or more pairs of electrons.
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4. Covalent Bonds H + H H : H = HH = H2 hydrogen molecule
Two nonmetal atoms form a covalent bond because they have less energy after they bonded
H H H : H = HH = H2
hydrogen molecule
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5. Double Covalent Bond 2 pairs of electrons are shared between 2 atoms
Example O2
       
 O   O   O::O
double bond
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6. Triple Covalent Bond 3 pairs of electrons are shared between 2 atoms
Example N2
       
 N   N   N:::N
 
triple bond
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7. Diatomic Elements
Elements that are naturally in molecules with 2 atoms each.
H, O, N, Cl, Br, I, F
Existing as diatomic molecule yields a stable octet
Gases that exist as diatomic molecules are H2, F2, N2, O2, Cl2, Br2, I2
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8. Learning Check
Use the name of the element to name the following diatomic molecules.
H2 hydrogen
N2 nitrogen
Cl2 _______________
O2 _______________
I2 _______________
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9. Solution
Use the name of the element to name the following diatomic molecules.
H2 hydrogen
N2 nitrogen
Cl2 chlorine
O2 oxygen
I2 iodine
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10. Lewis Structures Other molecules having single covalent bonds H2O
The hydrogens share their electrons w/ oxygen so that O has 8 e- and each H has 2 e-
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11. Covalent Bonds in NH3 Bonding pairs H   H : N : H
Lone pair of electrons
(unshared pair)
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12. Chemical Bonding: The Covalent Bond Model
Fig. 5.10
Linus Pauling received the Nobel Prize in chemistry in 1954 for his work on the nature of the chemical bond.
© Bettman/CORBIS
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H. Stephen Stoker

13. Bond Polarity: Nonpolar
Nonpolar covalent bond
Electrons are shared between atoms with the same or very close electronegativity values.
Examples:
N Br2
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14. Bond Polarity: Polar Polar covalent bond
Electrons are shared between different nonmetal atoms; Examples:
O-Cl O-S N-Cl
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15. Differences in E-Negativity
Your covalent bond will be Non-polar if the e-negativity difference is between 0 & .4
Your covalent bond will be polar if the e-negativity difference is between >.4 < 1.7

16. Chemical Bonding: The Covalent Bond Model
Fig. 5.12
(a) In the nonpolar covalent bond present, there is a symmetrical distribution of electron density. (b) In the polar covalent bond present, electron density is displaced because of its electronegativity.
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17. Learning Check Identify the type of bond between the following atoms
A. K-N
1) nonpolar ) polar 3) ionic
B. N-O
1) nonpolar 2) polar 3) ionic
C. Cl-Cl
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18. Solution A. K-N 3) ionic B. N-O 2) polar, covalent
C. Cl-Cl 1) nonpolar, covalent
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19. Electronegativity Material from karentimberlake.com and
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20. Writing Formulas Nonmetal/Nonmetal
In covalent bonds, the element with the lowest electronegativity is written first
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21. Chemical Bonding: The Covalent Bond Model
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22. Chemical Bonding: The Covalent Bond Model
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23. Naming of 2 Nonmetals Name each element End the last element in –ide
Add prefixes to show more than 1 atom
Prefixes
mon 1 hexa 6
di 2 hepta 7
tri 3 octa 8
tetra 4 nona 9
pent 5 deca 10
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24. Learning Check
Fill in the blanks to complete the following names of covalent compounds.
CO carbon ______oxide
CO2 carbon _______________
PCl3 phosphorus _______chloride
CCl4 carbon ________chloride
N2O _____nitrogen _____oxide
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H. Stephen Stoker
© Karen Timberlake

25. Learning Check P2O5 Cl2O7 Cl2 Material from karentimberlake.com and
H. Stephen Stoker

26. MOLECULAR GEOMETRY

27. Molecule adopts the shape that minimizes the electron pair repulsions.
MOLECULAR GEOMETRY
Molecule adopts the shape that minimizes the electron pair repulsions.
VSEPR
Valence Shell Electron Pair Repulsion theory.
Most important factor in determining geometry is relative repulsion between electron pairs.

28. Some Common Geometries
Linear
Tetrahedral
Trigonal Planar

29. VSEPR charts
Use the Lewis structure to determine the geometry of the molecule
Electron arrangement establishes the bond angles
Molecule takes the shape of that portion of the electron arrangement
Charts look at the CENTRAL atom for all data!
Think REGIONS OF ELECTRON DENSITY rather than bonds (for instance, a double bond would only be 1 region)

31. Structure Determination by VSEPR
Water, H2O
The electron pair geometry is TETRAHEDRAL
2 bond pairs
2 lone pairs
The molecular geometry is BENT.

32. Structure Determination by VSEPR
Ammonia, NH3
The electron pair geometry is tetrahedral.
The MOLECULAR GEOMETRY — the positions of the atoms — is TRIGONAL PYRAMID.