1. Chapter 16: Covalent Bonding
The Nature of Covalent Bonds

2. 4 Types of Covalent Bonds
1. Single Covalent bonds
2. Double Covalent bonds
3. Triple Covalent bonds
4. Coordinate Covalent bonds

3. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Single Covalent Bonds
Two atoms share one pair of electrons
Each atom ideally achieves an octet in a covalent bond so that they resemble the electron configuration of a noble gas
Structural formula is a chemical formula showing the arrangment of atoms in a molecule

4. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --

5. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Array of sodium ions and
chloride ions: Collection of water molecules:
Formula unit of
sodium chloride: Molecule of water:
Na Cl H O H
Chemical formula: NaCl Chemical formula: H2O

6. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Single Covalent Bonds
Covalent bonds result from combinations of nonmetals (I.e., group 4A, 5A, 6A, and 7A elements)
Unshared pairs
Also known as lone pairs
Pairs of valence electrons that are not shared between atoms of a molecule
Unshared pairs do not change form in a structural formula

7. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Single Covalent Bonds - Halogens

8. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Single Covalent Bonds – Larger Molecules

9. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Single Covalent Bonds – Larger Molecules

10. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Single Covalent Bonds – Larger Molecules
Spreading out the electrons
More stability
Less energy required
Preferred arrangements

11. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Double Covalent Bonds
Bonds that involve two shared pairs of electrons
Used to attain stable noble-gas configurations

12. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Double Covalent Bonds

13. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Double Covalent Bonds -- Exceptions
Oxygen gas (O2)
Expectation: formation of a double-bond to achieve octets
Evidence: formation of a single-bond with two electrons in the gas being unpaired

14. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Triple Covalent Bonds
Bonds that involve three shared pairs of electrons
Used to attain stable noble-gas configurations

15. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Coordinate Covalent Bonds
Covalent bond in which an atom contributes both bonding electrons
Structural formulas of coordinate covalent bonds show the bonds as arrows that point from the atom donating the pair of electrons to the atom receiving them
Examples
Carbon monoxide (CO)
Ammonium ion (NH4+)
Sulfur dioxide (SO2)

16. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Coordinate Covalent Bonds – Carbon Monoxide (CO)
An octet has been achieved for each molecule, but oxygen contributes the electrons needed.

17. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Coordinate Covalent Bonds – Ammonium Ion (NH4+)
An octet has been achieved for each molecule, but nitrogen contributes the electrons needed.

18. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Bond Dissociation Energies
Total energy required to sever the bond between two covalently bonded atoms
High in carbon compounds, resulting in high stability of carbon compounds
Table 16.3, page 448
Example: H – H kJ  H + H
This means that it would require 435 kJ of energy to break the bond between the two atoms in a hydrogen gas molecule (H2).

19. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Resonance
Structures that occur when it is possible to write two or more valid Lewis dot structures that have the same number of electron pairs for a molecule or ion
Structures are in constant resonance
NOTE: Single bonds are longer than double bonds; double bonds are longer than triple bonds

20. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Exceptions to the Octet Rule
Impossibilities occur where using the octet rule does not work.
Examples:
Nitrogen dioxide (NO2)
Oxygen gas (O2)
Phosphorus pentachloride (PCl5)
Sulfur hexafluoride (SF6)

21. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Exceptions to the Octet Rule – Nitrogen Dioxide (NO2)

22. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Exceptions to the Octet Rule – Phosphorus Pentachloride (PCl5)

23. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Exceptions to the Octet Rule – Sulfur Hexafluoride (SF6)

24. Chapter 16: Covalent Bonding -- The Nature of Covalent Bonding --
Exceptions to the Octet Rule
Cases for exceptions
More than 8 valence electrons
Less than 8 valence electrons
How to draw
Typically, the central atom will be the first one listed in the formula.
Hydrogens and halogens will typically surround the central atom.
Diamagnetic
Substance weakly repelled by a magnetic field
Paramagnetic
Substance strongly attracted to a magnetic field
These substances have molecules containing two or more unpaired electrons.
Not to be confused with ferromagnetism (as with magnets)
Mass if offset in a magnetic field