1. Chapter 8: Molecular Compounds
Chemistry

2. Covalent Bonding Covalent Bond: atoms held together by sharing e
Neither atom has the electronegativity to over power the other atom and take its electrons
“tug of war” between electrons
Co: with
Valent: refers to outermost electrons
Covalent: sharing of the outermost electrons between two atoms

3. Nomenclature - Covalent
Covalent bonds usually occur between two or more NONMETALS.
Named using Greek prefixes

4. Nomenclature - Covalent
In naming binary covalent compounds:
The first element retains its name and a prefix is used ONLY if there is more than one in the compound
The second element drops its ending and adds “-ide”; The second element ALWAYS gets a prefix
Ex: CO2 = Carbon dioxide

5. Practice Draw electron dot structures for each diatomic molecule:
Chlorine molecule
Bromine molecule
Iodine molecule
Oxygen
Fluorine molecule
Hydrogen
Nitrogen
H2O2
PCl3
NH3

6. Molecules and Molecular Compounds
Monatomic: elements existing in singular form.
Ex: Noble Gases (He, Ne, Ar, Kr…)

7. Molecules and Molecular Compounds
Molecule: neutral group of atoms joined by covalent bonds (neutral)
Diatomic Molecules: Molecule consisting of two atoms
Molecular Compounds: Compound composed of molecules
Low MP and BP
Gas and Liquid at room temp
Nonmetal + Nonmetal etc…
Ex: C + O  CO
Pg 214 good contrast between Ionic Compound and Molecular
NaCl and H2O

8. Molecules and Molecular Compounds
Molecular Formulas: chemical formula for a molecular compound
Shows # atoms of each element
Ex: H2O (2-H’s and 1-O)
Ex: C6H12O6 (6-C’s and 12-H’s and 6-O’s)

9. Molecules and Molecular Compounds
Diagrams and Models
Structural Formula
represents the covalent bonds by dashes

10. Molecules and Molecular Compounds
Diagrams and Models
Ball and stick Model

11. Molecules and Molecular Compounds
Diagrams and Models
Perspective Drawing

12. Molecules and Molecular Compounds
Diagrams and Models
Space Filling Molecular Model

13. 8.1 - Key Concepts
How are the MP’s and BP’s of molecular compounds different from those of ionic compounds?
What information does a molecular formula provide?

14. The Nature of Covalent Bonding
The Octet Rule: electrons tend to be transferred or shared so that each ion or atom acquires a noble gas e- configuration
Covalent bonds – atoms SHARE to attain a noble gas configuration

15. Covalent Bonding
Single Covalent Bonds: 2 atoms held together by sharing a pair of electrons
Ex: H2 H• + H•  H••H 1s1 + 1s1  1s2 (both look like He)
Halogens form SINGLE covalent bonds and DIATOMIC molecules

16. Covalent Bonding
Unshared pair: pair of valence e- not shared between atoms
AKA: lone pair or nonbonding pair
Ex: H2O contains 2 lone pairs
Ex: Ammonia NH3 contains 1 lone pair
Ex: Methane CH4 contains 0 lone pairs
PRACTICE: Draw e- Dot Structures for a)Chlorine b)Bromine c)Iodine
PRACTICE: Draw e- dot structure for compounds a)H2O2 b)PCl3

17. Covalent Bonding
Double Covalent Bonds: 2 atoms held together by 2 shared pairs of electrons
Ex: Oxygen O2

18. Covalent Bonding
Triple Covalent Bonds: 2 atoms held together by 3 shared pairs of electrons
Ex: Nitrogen N2

19. Covalent Bonding
Coordinate Covalent Bonds: a covalent bond in which one atom contributes both bonding electrons
The shard e- pair comes from one bonding atom
Ex: CO
Polyatomic Ion
Ex: NH4+
Ex: SO3 + 2e-  SO32-

20. Covalent Bonding
Bond Dissociation Energies: the energy required to break the bond between two covalently bonded atoms
A large bond dissociation energy corresponds to a strong covalent bond
BIG ENERGY = STRONG BOND

21. Covalent Bonding
Resonance: structure that occurs when it is possible to draw two or more valid e- dot structures that have the same # of e- pairs
Ex: Ozone O3 (protective layer that absorbs UV radiation from lower elevations it is a pollutant contributing to smog)

22. Covalent Bonding
Octet Rule Exceptions: cannot be satisfied in molecules whose:
Total # of Valence e- is an odd #
An atom has fewer or more than a complete octet of valence e-
NO2
PCl5
SF6

23. 8.2 - Key Concepts
What is the result of electron sharing in covalent bonds?
How do electron dot structures represent shared electrons?
How do atoms from double or triple covalent bonds?
How are coordinate covalent bonds different from other covalent bonds?
How is the strength of a covalent bond related to its bond dissociation energy?
How are oxygen atoms bonded in ozone?
What are some exceptions to the octet rule?

24. Bonding Theories
Molecular Orbitals: orbitals that apply to the entire molecule.
Molecular orbital belongs to the whole molecule
Bonding Orbital: molecular orbital that can be occupied by 2 e- of a covalent bond
Where the bonding occurs**
Sigma Bond: 2 atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting 2 atomic nuclei (σ)
‘s’ orbitals or ‘p’ orbitals

25. Bonding Theories
Sigma Bond

26. Bonding Theories
Pi Bond: bonding electrons are most likely found above/below axis
Weaker than sigma
Pi overlap less than Sigma

27. VSEPR Theory VSEPR Theory: explains 3D shapes
Repulsion between e- pairs causes molecular shapes to adjust so that the valence e- pairs stay as far apart as possible.
Unshared Pairs – important predictors of the molecular shapes

28. VSEPR Theory
Linear Triatomic
AX2
Trigonal Planar
AX3
Tetrahedral
AX4

29. VSEPR Theory
Pyramidal
AX3
Trigonal bipyramidal
AX5
Octahedral
AX6

30. VSEPR Theory
T-shaped
AX3
Bent triatomic
AX2
Square planar
AX4

31. Polar Bonds and Molecules
Nonpolar Covalent Bond:
Bond is pulled equally
Bonding e- are equally shared
H2, O2… Diatomic

32. Polar Bonds and Molecules
Polar Covalent Bond:
Bond is unequal
Bonding e- are unequally shared
The more electronegative atom attracts electrons more strongly and gains a slightly negative charge

33. Polar Bonds and Molecules
Polar molecules: one end is slightly negative and other is slightly positive
Dipole: molecule that has two poles (dipolar)
When polar molecules are placed between opp. Charged plates, they orient with respect to positive and negative plates pg. 239

34. Polar Bonds and Molecules
Intermolecular Attractions:
Weaker than ionic or covalent bonds
1)Van der Waals Forces:
Dipole interactions
Dispersion forces
WEAKEST
2) Hydrogen Bonds
Attractive forces in which a H covalently bonded to a very electronegative atom is weakly bonded also to an unshared e- pair.