1. Chemistry
Tuesday!!!!! 1/24/12
Bell Ringer
Schedule
1. Pick up the Ionic bond packet off the front demo table. Write down and answer the following questions on your packet somewhere.
A. Identify the valence electrons and electron dot drawing of the following elements:
Li Ca Al
C P S
F Ne
Bell Ringer
Ionic & Covalent Bonding Demo
Ionic/Covalent Bonding Notes
HOMEWORK: Practice problems in your packet
I CAN… compare and diagram ionic and covalent bonding.

2. Li Ca Al C P S F Na

3. Chemical Bonding and Molecular Structure
Cartoon courtesy of NearingZero.net

4. Bonding
Chemical Bond
attractive force between atoms or ions that binds them together as a unit
bonds form in order to…
decrease potential energy (PE)
increase stability

5. Intra VS Intermolecular Forces
INTRA within
INTER between, among
Intramolecular force: bonds between atoms or ions in molecules Examples: metallic, covalent, & ionic bonds
Hydrogen bonds to oxygen and forms water
Intermolecular force: attraction between molecules themselves Intermolecular forces are only associated with covalently bonded molecules (glucose & fructose hydrogen bridge to make sucrose)
3 different levels of strength:
1) Hydrogen Bridge (used to be called H bond) (strongest)
2) Dipole-dipole forces
3) London Dispersion forces
(weakest) (covalently bonded molecules have this)
Water molecule attracted to another water molecule

6. Review of Chemical Bonds
There are 2 main types of bonding:
IONIC—transfer of 1 or more valence electrons
COVALENT—sharing of valence electrons
“Between ionic and covalent most bonds are”

7. The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

8. Electronegativity Difference
If the difference in electronegativities is between:
1.7 to 4.0: Ionic
0.3 to 1.7: Polar Covalent
0.0 to 0.3: Non-Polar Covalent
Example: NaCl
Na = 0.8, Cl = 3.0
Difference is 2.2, so
this is an ionic bond!

9. Ionic Bonds
Ions are positively or negatively charged atoms due to the removal or addition of an ELECTRON
CATION (CAT – ION) is positively charged – electron removed.
ANION (AN – ION) is negatively charged – electron gained.
In general
metals (Mg) lose electrons ---> cations (+)
nonmetals (F) gain electrons ---> anions (-)

10. Ionic Bonds
Positive cations and the negative anions are attracted to one another (remember: Opposites Attract!)
Therefore, ionic compounds are usually between metals and nonmetals (opposite ends of the periodic table).

11. Comparison Ionic Compounds Covalent Compounds
Crystalline solids (made of ions)
High melting and boiling points
Conduct electricity when melted
Many soluble in water but not in nonpolar liquid
Metal and nonmetals bond
Gases, liquids, or solids (made of molecules)
Low melting and boiling points
Poor electrical conductors in all phases
Many soluble in nonpolar liquids but not in water
Nonmetals bond with other nonmetals

15. Covalent Bond
A chemical bond in which two or more electrons are shared by two atoms.
How should two atoms share electrons?
7e-
7e-
8e-
8e- F F + F
Lewis structure of F2
lone pairs F
single covalent bond
single covalent bond F

16. Lewis structure of water
single covalent bonds
2e-
8e-
2e- H + O + H O H or
Double bond – two atoms share two pairs of electrons
8e-
8e-
8e-
double bonds O C or O C
double bonds
Triple bond – two atoms share three pairs of electrons
triple bond
8e- N
8e- or N
triple bond

17. Polarity
A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment.

18. + - Dipole Moment H Cl Direction of the polar bond in a molecule.
Arrow points toward the more electronegative atom.
H Cl + -
Courtesy Christy Johannesson 18

19. Polar Covalent Bond Electrons are shared unequally
A covalent bond with greater electron density around one of the two atoms resulting in partial charges (dipole) H F
e- poor
e- rich
electron rich
region F H
electron poor
region d+ d-

20. Bond Polarity
HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity)
Cl has a greater share in bonding electrons than does H.
Cl has slight negative charge (-d) and H has slight positive charge (+ d)

21. Bond Polarity
This is why oil and water will not mix! Oil is nonpolar, and water is polar.
The two will repel each other, and so you can not dissolve one in the other

22. Bond Polarity “Like Dissolves Like” Polar dissolves Polar
Nonpolar dissolves Nonpolar

23. Determining Molecular Polarity
Nonpolar Molecules
-Electrons are shared equally
-Symmetrical electron density
-Often identical atoms
-Dipole moments are symmetrical and cancel out.
BF3 F 23

24. Polar Bonds .. .. .. F O N H Cl H H H B H H F F Polar Polar NonpolarXe Cl C C Cl F F Cl H F F Cl H
Polar
Nonpolar
Nonpolar
Polar
A molecule has a zero dipole moment because their dipoles cancel one another. 24

25. Hydrogen Bonding Occurs with polar structures only
Includes a positive Hydrogen ion bonding directly to a negative ion
Examples: H-O H-N H-F H2O
DNA, RNA, and enzymes have many Hydrogen bonding sites
Strongest intermolecular force 25

26. London Dispersion forces
Also known as van der Waals bonds
Occur only with nonpolar structures
Weakest intermolecular force
Electrostatic bonds between atoms or molecules
Temporary dipole moment 26

27. Lewis Dot Bonding
Write down examples on board

28. Double and even triple bonds are commonly observed for C, N, P, O, and S
H2CO
SO3
C2F4

29. 1/25/10 MONDAY
Bell Ringer:
Pick up the Molecular Geometry packet off the front green demo table.
Remember, we needs Dots candy and toothpicks if you want to perform the edible lab 

30. MOLECULAR GEOMETRY

31. VSEPR MOLECULAR GEOMETRY Valence Shell Electron Pair Repulsion theory.
Molecule adopts the shape that minimizes the electron pair repulsions.
VSEPR
Valence Shell Electron Pair Repulsion theory.
Most important factor in determining geometry is relative repulsion between electron pairs.

32. Some Common Geometries
Linear
Tetrahedral
Trigonal Planar

34. Other VSEPR charts

35. Structure Determination by VSEPR
Water, H2O
The electron pair geometry is TETRAHEDRAL
2 bond pairs
2 lone pairs
The molecular geometry is BENT.

36. Structure Determination by VSEPR
Ammonia, NH3
The electron pair geometry is tetrahedral.
The MOLECULAR GEOMETRY — the positions of the atoms — is TRIGONAL PYRAMID.