1 / 28

Lecture 9

Lecture 9. Lewis Structures and Covalent Bonds 2.5-2.8 10 -September Assigned HW 2.33, 2.34, 2.35, 2.36, 2.38, 2.43, 2.48, 2.50, 2.52 Due : Monday 13-Sept. Review 2.1-2.4. Ions interact in specific ways that form crystal lattices

binta
Télécharger la présentation

Lecture 9

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 9 Lewis Structures and Covalent Bonds 2.5-2.8 10-September Assigned HW 2.33, 2.34, 2.35, 2.36, 2.38, 2.43, 2.48, 2.50, 2.52 Due: Monday 13-Sept

  2. Review 2.1-2.4 • Ions interact in specific ways that form crystal lattices • The energy that stabilizes these lattices, called lattice energy is dependent on • The charges of the ions • The ionic radius • Madelung constant (A)  dependent on the orientation of the ions • Including an additional term allows us to accurately predict the lattice energy • Lewis Representation of atoms and Ions • Valence electrons are represented by dots • Single dot = unpaired electron • Pair of dots = paired electrons within an atomic orbital

  3. Compounds Compound Bond Type Inorganic Compound Organic Compound Covalent Composed of Charged components Ionic Bonds Contains Carbon Cations Anions

  4. Lewis Representation – Ionic Bond • American chemist G.N. Lewis had a profound impact on our understanding of chemical bonding. One of his many contributions was a simple way to represent chemical bonds. We call these Lewis Symbols. • Valence Electrons are represented by dots. • A single dot represents an electron • A pair of dots represents two paired electrons sharing an orbital H He N O Cl K Mg I 1s1 1s2 2s22p3 2s22p4 2s22p5 3s1 5s25p5 3s2

  5. Ionic Bonds – CaCl2 Ion Ca2+Cl- Electron Configuration [Ar] [Ne]2s22p6 Lewis Symbol Ionic bonds do not share electrons – bond due to coulombic attraction

  6. Lewis Representation – Covalent Bonds Covalent bonds  electrons shared between two atoms. This involves an overlap of atomic orbitals Let’s consider H2 - two hydrogen atoms share electrons. H• H H + H• Commonly represented as: H H Solid line represents covalent bond

  7. Lewis Representation – Covalent Bonds F2 Only the unpaired electron is involved in bonding. F• F F + F• F F How would this look if we were making Cl2?

  8. Lewis Representation – Covalent Bonds HF Start Finish The Octet Rule – non-metals share electrons until each has a complete octet (or duplet for H and He).

  9. Lewis Representation – Covalent Bonds CH4 Start Finish C H H H H Have we satisfied the octet rule?

  10. Common Representations of Compounds

  11. Common Representations of Compounds Ethanol Chemical Formula: C2H6O Tells us what is there Molecular Formula: CH3CH2OH Gives us information about the arrangement of the atoms OH Stick Ball and stick Spacefill

  12. Lewis Structures

  13. Lewis Structures Ethanol CH3CH2OH C  4 x 2 = 8 H  1 x 6 = 6 O  6 x 1 = 6 20

  14. Lewis Structures Ethanol CH3CH2OH C  4 x 2 = 8 H  1 x 6 = 6 O  6 x 1 = 6 20 20 – 16 = 4 left

  15. Lewis Structures – common groups

  16. Lewis Structures Formaldehyde CH2O C  4 x 1 = 4 H  1 x 2 = 2 O  6 x 1 = 6 12 Make skeleton Fill boxes with electron pair Fill terminal atoms octet Make multiple bonds 12 – 12 = 0 left Are all octets full? Are all octets full?

  17. Lewis Structures Ethyl Aldehyde CH3CHO 1 C  4 x 2 = 8 H  1 x 4 = 4 O  6 x 1 = 6 18 2 4 3 18 – 18 = 0 left Are all octets full?

  18. Bond Order Bond Order  the number of bonds that link a specific pair of atoms. BO = ½ x (# of shared electrons) 1  single bond 2  double bond 3  triple bond 1 1 1 1 1 2 3 1

  19. Lewis Structures Carbonic Acid H2CO3 C 4 x 1 = 4 H  1 x 2 = 2 O  6 x 3 = 18 24 When you see hydrogen first in molecular formula, think acid. H is attached to an Oxygen Make skeleton Fill boxes with electron pair Fill terminal atoms octet Fill central atoms octets 24 – 16 = 8 left 24 – 24 = 0 left Are all octets full? Are all octets full?

  20. Lewis Structures Carbonic Acid H2CO3 24 – 24 = 0 left Are all octets full? Make a double bond

  21. Formal Charge We’ll determine which structure is the most stable by inspecting the charge on each atom. Formal Charge = V – (LP + B) # valence electrons in free atom Total Bond Order # electrons in lone pair

  22. Formal Charge We’ll determine which structure is the most stable by inspecting the charge on each atom. Formal Charge = V – (LP + B) # valence electrons in free atom Total Bond Order # electrons in lone pair +1 0 0 0 0 0 -1 -1 0 0 0 0 0 0 0 +1 0 0

  23. Formal Charge We’ll determine which structure is the most stable by inspecting the charge on each atom. Formal Charge = V – (LP + BO) # valence electrons in free atom Total Bond Order # electrons in lone pair Carbon and Hydrogen same 3 types of Oxygens in these structures +1 0 0 0 -1 -1 0 0 0 0 +1 0

  24. Formal Charge Carbonic Acid H2CO3 Most stable structure has minimized charge Net charge on the molecule is the sum of all formal charges. +1 0 0 0 0 0 -1 -1 0 0 0 0 0 0 0 +1 0 0

  25. Formal Charge We’ll determine which structure is the most stable by inspecting the charge on each atom. Most stable structure has minimized charge 0 0 0 0 0 0

  26. Formal Charge and Ions What happens when we remove 2 H+? Carbonate CO32- 2H+

  27. Formal Charge and Ions What happens when we remove 2 H+? Carbonate CO32- 2H+ So the 2- charge on carbonate is localized to two oxygens?

  28. Formal Charge and Ions Carbonate CO32- We can draw this structure three equivalent ways! RESONANCE STRUCTURES We can conclude that 2- charge on carbonate is SHARED amongst the oxygens

More Related