Chapter 9: Chemical Bonding I: Lewis Theory

1. Chapter 9: Chemical Bonding I: Lewis Theory CHE 123: General Chemistry I Dr. Jerome Williams, Ph.D. Saint Leo University

2. Overview Lewis Structures Examples of Lewis Structures

3. Lewis Structures Using electron-dot (Lewis) structures, the valence electrons in an element are represented by dots. Valence electrons are those electrons with the highest principal quantum number (n).

4. Lewis Structures Two Global Concepts 1. Lewis structures - valence electrons are our focus. We divide valence electrons into two groups. Bonding electrons connect atoms (these are called bonds) Nonbonding (Lone Pairs) are found on atoms 2. A bond = a pair of electrons ( represented as : or - ).

5. Figure: 09-04-01UN Title: Valence Electrons Caption: Before drawing a Lewis structure, we need to know the number of valence electrons.Figure: 09-04-01UN Title: Valence Electrons Caption: Before drawing a Lewis structure, we need to know the number of valence electrons.

6. Figure: 09-04-02UN Title: Oxygen's Lewis Structure Caption: Before drawing a Lewis structure, we need to know the number of valence electrons. Oxygen will have six dots.Figure: 09-04-02UN Title: Oxygen's Lewis Structure Caption: Before drawing a Lewis structure, we need to know the number of valence electrons. Oxygen will have six dots.

7. Figure: 09-06-08UN Title: Bonding pairs Caption: In covalent bonding, bonding pairs are generally formed when an electron from each atom participating in the bond is shared by both atoms.Figure: 09-06-08UN Title: Bonding pairs Caption: In covalent bonding, bonding pairs are generally formed when an electron from each atom participating in the bond is shared by both atoms.

8. Lewis Structures How to Draw Lewis Structures 1. Determine total number valence electrons in molecule or ion. Remember to account for charges. 2. Find central atom and place in center. Do not choose hydrogen since it only forms 1 bond (Duet rule) First atom in formula (except H) usually central atom

9. Figure: 09-06-07UN Title: Duets Caption: Hydrogen is an exception to the octet rule: it requires only two electrons to be at low energy.Figure: 09-06-07UN Title: Duets Caption: Hydrogen is an exception to the octet rule: it requires only two electrons to be at low energy.

10. Lewis Structures How to Draw Lewis Structures 3. Draw skeletal structure by surrounding central atom with other atoms in as symmetrical a pattern as possible. 4. Connect atoms with single bonds. Be sure to subtract valence electrons used from the total.

11. Lewis Structures How to Draw Lewis Structures 5. Distribute remaining electron pairs around exterior atoms as lone pairs so everyone (except H) is FDH. Subtract these electrons from your total. 6. Put remaining pairs on central atom. Share lone pairs between bonded atoms to create multiple bonds.

12. Figure: 09-06-10UN Title: Octets in an oxygen molecule Caption: In oxygen, a double bond forms when two electrons from each atom are shared by both atoms.Figure: 09-06-10UN Title: Octets in an oxygen molecule Caption: In oxygen, a double bond forms when two electrons from each atom are shared by both atoms.

13. Figure: 09-06-12UN Title: Octet in hydronium Caption: The hydronium ion is stable in aqueous solutions because its oxygen has an octet.Figure: 09-06-12UN Title: Octet in hydronium Caption: The hydronium ion is stable in aqueous solutions because its oxygen has an octet.

14. Lewis Structures

15. Examples of Lewis Structures ammonia carbon dioxide ammonium cation

16. Figure: 09-13-01UN Title: EXAMPLE 9.5 Writing Lewis Structures - Hydrogen Caption: Write a Lewis Structure for NH3.Figure: 09-13-01UN Title: EXAMPLE 9.5 Writing Lewis Structures - Hydrogen Caption: Write a Lewis Structure for NH3.

17. Figure: 09-13-03UN Title: Ammonia molecule featuring its lone pair Caption: Ammonia's lone pair helps the N atom to achieve its octet.Figure: 09-13-03UN Title: Ammonia molecule featuring its lone pair Caption: Ammonia's lone pair helps the N atom to achieve its octet.

18. Figure: 09-13-04UN Title: Double bond in carbon dioxide Caption: Pairs of electrons from the oxygen will form double bonds in carbon dioxide that lead to atoms having octets.Figure: 09-13-04UN Title: Double bond in carbon dioxide Caption: Pairs of electrons from the oxygen will form double bonds in carbon dioxide that lead to atoms having octets.

19. Figure: 09-13-05UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - Skeletal Structure Caption: Write the Lewis structure for the NH4+ ion.Figure: 09-13-05UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - Skeletal Structure Caption: Write the Lewis structure for the NH4+ ion.

20. Figure: 09-13-06UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - Lewis Structure Caption: Write the Lewis structure for the NH4+ ion.Figure: 09-13-06UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - Lewis Structure Caption: Write the Lewis structure for the NH4+ ion.

21. Figure: 09-13-07UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - 8 of 8 electrons used Caption: Write the Lewis structure for the NH4+ ion.Figure: 09-13-07UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - 8 of 8 electrons used Caption: Write the Lewis structure for the NH4+ ion.

22. Figure: 09-13-08UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - Lewis structure in brackets with charged ion Caption: Write the Lewis structure for the NH4+ ion.Figure: 09-13-08UN Title: EXAMPLE 9.6 Writing Lewis Structures for Polyatomic Ions - Lewis structure in brackets with charged ion Caption: Write the Lewis structure for the NH4+ ion.

23. Examples of Lewis Structures

24. Examples of Lewis Structures

25. Examples of Lewis Structures

26. Examples of Lewis Structures Exceptions to Octet Rule Polyatomic molecules with central atoms below the second row can break octet rule due to available empty d-orbitals. Free radicals that contain odd number valence electrons. Electron deficient species that prefer to not have an octet (for examples see elements Be or B).

27. Figure: 09-14-17UN Title: Chemical Structure - Octet Violators Caption: Elements in the third row of the periodic table and beyond often exhibit expanded octets of up to 12 (and occasionally 14) electrons.Figure: 09-14-17UN Title: Chemical Structure - Octet Violators Caption: Elements in the third row of the periodic table and beyond often exhibit expanded octets of up to 12 (and occasionally 14) electrons.

28. Figure: 09-14-13UN Title: Chemical structure BF3 Caption: Boron forms compounds with only six electrons around B, rather than eight.Figure: 09-14-13UN Title: Chemical structure BF3 Caption: Boron forms compounds with only six electrons around B, rather than eight.

29. Examples of Lewis Structures Draw electron-dot structures for: C3H8 H2O2 CO2 N2H4 CH5N C2H4 C2H2 Cl2CO

30. Examples of Lewis Structures Draw electron-dot structures for: SF4 SF6 XeOF4 XeF5+ XeF4 H3S+ HCO3�