1. Bonding & Molecular Shapes
Dr. Ron Rusay
Spring 2004
© Copyright 2004 R.J. Rusay

2. Chemical Bonds Definition:
Attraction between atoms that hold them together. Bonds provide a particular arrangement of atoms in a molecule which provides it with new chemical properties.

3. Table salt: Sodium chloride
Water

4. Ionic vs. Covalent Bonding

5. Electron Configurations Noble Gases and The Rule of Eight
A nonmetal and a metal react to form an ionic compound: Valence electrons of the metal are lost and the nonmetal gains these electrons. (Ionic Bonding)
When two nonmetals react: They share electrons to achieve a Noble Gas Configuration. (Covalent Bonding)
Where are metals and non-metals located in the
Periodic Table?

6. Lewis Electron-Dot Symbols for Elements in Periods 2 & 3
How many valence electrons does each element have in each of the vertical columns (families)?

7. Ionic Bonds
Result from electrostatic (positive-negative) attractions of closely packed, oppositely charged ions.
Form when an atom which can easily lose electrons (low electronegativity) reacts with one which can easily gain electrons (high electronegativity).
Na and Cl; Fe and O

8. Covalent Bond Lengths The distance between atoms.
It is the distance that provides the most stable arrangement of the atoms where the bond energy is at a minimum.

9. Covalent Bonding & Bond Length

10. Bond Lengths and Covalent Radius

11. Bond Lengths : Bond Strengths
The Periodic Table
Bond Lengths : Bond Strengths

13. Actual vs. Expected Bond Length
Actual = nm
Expected = nm

14. Electronegativity

15.  = (H  X)actual  (H  X)expected
Electronegativity
The ability of an atom in a molecule to attract shared electrons to itself.
 = (H  X)actual  (H  X)expected

17. Periodic Trend

18. Electronegativity Differences & Polar Covalent Bonds
A molecule with a relatively high difference in electronegativities, such as HF, has a center of positive charge and a center of negative charge. It is polar, having an experimentally measureable dipole moment.

19. The spectrum of bond differences: Ionic at one extreme : Non-polar covalent at the other.

20. Bond Shapes

21. Lewis Structure
Shows how valence electrons are arranged among atoms in a molecule.
Reflects central idea that stability of a compound relates to noble gas electron configuration.

22. Lewis Structure of Water

25. Fundamental Bonding Patterns
Carbon has a total of four bonds:
4 single bonds
2 single bonds plus 1 double bond
1 single bond plus 1 triple bond
Oxygen has a total of 2 bonds plus 2 “free pairs of electrons”:
2 single bonds
1 double bond

26. Fundamental Bonding Patterns
Nitrogen has a total of three bonds plus 1 “free pair of electrons”:
3 single bonds
1 single bonds plus 1 double bond
1 triple bond
Hydrogen only has 1 single bond.
This is the total of almost all bonding arrangements in organic molecules.

27. Lewis Structures of Simple MoleculesH H H N
. . H H
. .
. . N N
Ammonia H H C
. . O
. .
Urea

29. Carbonate Ion CO32- :
The carbonate polyatomic ion has two coordinate bonds, resonance forms and two electrons from a cation!

30. The Lewis Structure for Sulfur trioxide

31. Where to draw the sulfur-oxygen double bond? There are three options.
Simplified drawings without free pairs of electrons:
Experimental data shows that each of the three sulfur-oxygen bonds are the same length.

32. Resonance
Occurs when more than one valid Lewis structure can be written for a particular molecule.
These are resonance structures. The actual structure is an average of the resonance structures.

33. Delocalized Electron-Pairs
Resonance:
Delocalized Electron-Pairs
Ozone : O3 .. .. .. .. .. O O .. .. .. .. .. .. O O .. O O II I
Resonance Hybrid Structure .. O .. .. .. .. O O
One pair of electron’s resonates
between the two locations!!

34. Ozone and CFCs
CCl2F2 O .. .. .. .. O O C Cl F .. ..
Freon 12 ..

35. VSEPR Model Valence Shell Electron Pair Repulsion

36. VSEPR Model
The molecular structure which surrounds a given atom is determined principally by minimizing electron pair repulsions through maximizing separations.

37. Molecular Models Computer Generated Models
Ball and stick models of ammonia, water and methane. For many others see: