1. Chemical Bonding

2. Outline for Chemical Bonding
General bonding information
Ionic compounds and their properties.
1.naming ionic compounds.
Covalent compounds
Lewis dots
Shapes of molecules
Polar and nonpolar molecules
Summary of covalent compounds.
Metals and metallic bonding

3. General information
All bonds are the result of a (+) and (-) attraction.
Only valence e- are directly involved in bonding
A pair of valence e- makes one bond.
Transitional metals may have their valence e- come from the last two E.L.

4. Properties of ionic compounds
An atom which loses electrons combines with an element that gains electrons.
A cation and an anion are formed in ionic bonds.
Ionic charges are used to determine the empirical formula. Ex CaCl2, K2S
Ionic compounds form crystals
have a distinct geometric arrangement
are brittle and so shatter when hit.

5. Properties of Ionic crystals continued
high melting points.
When dissolved in water - form free moving ions which conduct electricity.
molten state - semi conductors, ions can only slide over each other very slowly.
not conductive as solids- no movement in the ions.

6. Model of an NaCl crystal

7. Photos of ionic crystals

8. Photos ionic crystals

9. Properties of most covalent compounds
Rarely break apart to form ions in water.
Usually they do not conduct electricity under any circumstance.

10. Molecular geometry The shape of a molecule depends on:
The number of outer atoms.
The central atom’s number of valence e-. Specifically, are there any unbonded valence e?

11. Some examples of shapes

12. Pyramidal shape molecule

13. Covalent compounds can be divided into 2 categories
Polar covalent
Molecules have a (+) and (-) end (dipole) to them.
A dipole is created when there is a difference of 0.5 or greater in electronegativity
A dipole is created when F,O,N, or Cl is in the molecule and they are not bonded to an identical element.
HI MRS.TURNER
Nonpolar covalent
Molecules have no charge on them
Either there are no dipoles, or the dipoles cancel out.
dumb

14. Determining whether a covalent compound is polar or nonpolar.
First: determine if there are any bonds with dipoles in the molecule.
Second: determine the shape of the molecule.
Third: determine if the dipoles cancel on the molecule. If they cancel, the molecule is nonpolar. If they add up to create a (+) or (-) end, then the molecule is polar.

15. First step: determining dipoles
A dipole is a bond with a (+) end and a (-) end.
Dipoles are created when F,O,N, and Cl, are bonded to any other element other than itself.
Exception: N bonded to Cl does not make a dipole.

16. Dipoles continued Determine which bonds have dipoles;
N-F, C-S, N-Br, O=O, N-Cl, H-S, N-H, H-O
The bonds with dipoles are: N-F, N-Br, N-H, H-O
The element which is more electronegative will have a partial (-) charge, the other element will have a partial (+) charge.

17. Second step. Determine the shape
Use your chart on molecular geometry to determine the shape of the molecule.
Note the number of outer atoms and if the central atom has an unbonded pair of valence electrons. Example: BH3 and NH3 BH3 is planar, but NH3 is pyramidal because the “N” has an unbonded pair of e-

18. Third and final step. Determining whether a molecule is polar or nonpolar.
Applying the rules:
Example: NF3
Time to use the whiteboard!!!!!
Leave space in your notes to write several examples .

19. Differences between the physical properties of polar and nonpolar molecules
Not soluble in water, makes a separate layer from water.
Volatile- easily evaporate
Low melting and boiling points.
Not very dense
At room temp.: small molecules are gases, larger ones are liquids or soft solids.
Polar molecules
Soluble in water
Low volatility- do not evaporate easily
Relatively high melting and boiling points for their molar mass.
More dense than non polar
At room temp. very few are gases, most are liquids and solids.
Solids have crystal lattices

21. Examples of polar and nonpolar substances
Water
Vinegar
Blood
Alcohols
HCl
Acetone
Sugars
hair
Nonpolar substances
Oils
Waxes
Most fuels, ex. Gasoline, methane
paint thinner
Sulfur.
Oil base paints

22. Summary of the Two types of bonds
Ionic Bonds
Occur between metals and nonmetals
Occur between an element with a low IE and one with a high IE
Metal loses e- to the nonmetal
Attraction is between an anion and a cation, (so ions are present).
Covalent bonds
Occurs between nonmetals only
Both elements have high IE
Valence e- are shared
No ions are formed but dipoles may form.

23. Summary of the compounds
Ionic compounds
Form crystals
Compounds found in rocks, minerals, bones
Conduct only when molten or aqueous
Many compounds dissolve in water.
Covalent compounds
Only polar ones make distinct crystals
Found in living things
Rarely conductive electricity.
Only polar molecules dissolve in water

24. Van der Waals
Dipole-dipole interaction
Hydrogen bonding