1. Chapter 8
Covalent Bonding

2. Molecular Compounds
8.1

3. Molecules and Molecular Compounds
Atoms that are held together by sharing electrons are joined by a covalent bond
A molecule is a neutral group of atoms joined together by covalent bonds
A diatomic molecule contains two atoms
Rule of Thumb: Hydrogen 7, make a 7
H2, O2, N2, F2, Cl2, Br2, I2
A compound composed of molecules is called a molecular compound
A molecular formula is the chemical formula of a molecular compound

4. What information does a molecular formula provide?
Key Question
What information does a molecular formula provide?
The amount of atoms of each element a substance contains.
Molecular compounds are made up of nonmetals
Molecular compounds typically have low melting and boiling points, this is due to the intermolecular forces; which will be discussed later in the chapter
The arrangement of the atoms within a molecule is called its molecular structure

5. The Nature Of Covalent Bonding
8.2

6. The Octet Rule in Covalent Bonding
Key Question What is the result of electron sharing in covalent bonds? The atoms attain an electron configuration of a noble gas by sharing a pair of electrons. Atoms may also form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons. REMEMBER… The octet rule states that an atom will gain or lose electrons to become stable (8 valence electrons) like a noble gas!

7. A bond formed by sharing three pairs of electrons is a triple bond
Two atoms held together by sharing one pair of valence electrons are joined by a single covalent bond
A structural formula represents the covalent bonds as dashes and shows the arrangement of covalently bonded atoms
A pair of valence electrons that is not shared between atoms is called an unshared pair
An unshared pair is also referred to as a lone pair or nonbonding pair
A double covalent bond is a bond that involves two shared pairs of electrons
A bond formed by sharing three pairs of electrons is a triple bond

8. Exceptions To The Octet Rule
Key Question What are some exceptions to the octet rule? The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number. There are also molecules in which an atom has less, or more, than a complete octet of valence electrons.

9. DRAWING LEWIS DOT STRUCTURES (electron dot structures)
In Class ONLY!

10. Rules For Drawing Lewis Dot Structures
Sum valence electrons from all atoms
Place least electronegative in the center, except H!
WHY?
Write the symbols for the atoms to show which atoms are attached to which, and connect them with a single bond to the central atom
Complete octets around all the atoms bonded to the central atom, starting with the most electronegative atom
Place left over electrons on the central atom
If there are not enough electrons to give the central atom an octet, try multiple bonds
Begin shifting from the most electronegative
OLD RULE OF THUMB
O likes double bonds, N likes triple bonds

11. Model and Practice Drawing Lewis Dot Structures
See Study Guide
Model and Practice Drawing Lewis Dot Structures
In Class ONLY!

12. Bond Dissociation Energies
The energy required to break the bond between two covalently bonded atoms is the bond dissociation energy
Key Question
How is the strength of a covalent bond related to its bond dissociation energy?
A large bond dissociation energy corresponds to a strong covalent bond.

13. See Study guide
You will need Table 8.3 on page 236. Model and Practice Calculating Bond Dissociation Energy
In Class ONLY!

14. Bonding Theories
8.3

15. VSEPR Theory VSEPR Valence Shell Electron Pair Repulsion Theory
Key Question
What do scientists use the VSEPR theory for?
To explain the three-dimensional shape of molecules.
VSEPR theory states that the repulsion between electron pairs causes molecular shapes to adjust so that the valence electron pairs stay as far apart as possible
The sum of the bonding electrons and lone pair electrons makes up what is called the electron domain geometry
The electron domain geometry can be predicted by using summing the number of bonding electrons and lone pair electrons

16. Model and Practice Predicting the Electron Domain Geometry
See Study Guide
Model and Practice Predicting the Electron Domain Geometry
In Class ONLY!

17. The molecular geometry of a substance is predicted by separating the bonding electrons from the lone pair of electrons

18. Model and Practice Predicting Molecular Geometry
See Study Guide
Model and Practice Predicting Molecular Geometry
In Class ONLY!

19. Polar Bonds and Molecules
When the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally, and each bond formed is a nonpolar covalent bond
H2, O2, N2, F2, CO2 all have nonpolar covalent bonds
Polar covalent bond (polar bond) is a covalent bond between atoms in which the electrons are shared unequally
Whether a substance is polar or not depends on electronegativity
REMEMBER…
Electronegativity increases from the bottom to the top and from left to right.

20. Key Question How do electronegativity values determine the charge distribution in a polar bond? The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less-electronegative atom has a slightly positive charge. See page 248 for the symbols that are used to denote polarity.

21. Model and Practice Predicting the Polarity of a Substance
See Study Guide
Model and Practice Predicting the Polarity of a Substance
In Class ONLY!

22. A molecule that has two poles is called a dipolar molecule or a dipole
A polar molecule has one end that is slightly negative, and another end that is slightly positive
A molecule that has two poles is called a dipolar molecule or a dipole
Why do the following substances have dipole moments?
SiCl, H2O, HCl
Does CO2 have a dipole moment? Explain.

23. Attractions Between Molecules
Key Question How do the strengths of intermolecular attractions compare with ionic and covalent bonds? Intermolecular attractions are weaker than either ionic or covalent bonds.

24. The two weakest attractions between molecules are collectively called van der Waals forces
Van der Waals forces consists of dipole interactions and dispersion forces
Dipole interactions occur when polar molecules are attracted to one another
The slightly polar negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule
Dipole interactions are similar to, but much weaker than ionic bonds
See page 250 (could go way more in depth ion-dipole, dipole-dipole)
Dispersion forces are the weakest of all molecular interactions and are caused by the motion of electrons
They occur between nonpolar molecules
CH4

25. Do the following exhibit hydrogen bonding? Explain.
Hydrogen bonds are attractive forces in which hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom
In order for hydrogen bonding to take place a covalent bond must already exist between hydrogen and either N, O, or F, and a lone pair of electrons must be present on the central atom (N, O, F)
Do the following exhibit hydrogen bonding? Explain.
NH3, CH4, CH3F, H2S, H2O

26. Intermolecular Attractions and Molecular Properties
Key Question Why are the properties of covalent compounds so diverse? Intermolecular attractions!