Chapter 16: Covalent Bonding

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 + 435 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