7
Unit 12 Notes: Chemical Bonding &
Molecular Geometry
Chemical Bonds
A. Chemical Bonds
B. Types of Chemical Bonds
1. Ionic
2. Covalent Bonds
3. Metallic Bonds
C. Octet rule (Rule of 8)
D. Examples of Bonding Types
1. Ionic Bonding
2. Covalent Bonding
3. Metallic Bonding
Lewis Dot Diagrams (Ionic Compounds)
A. Lewis Dot Diagrams
A Lewis dot diagram depicts ______.
Ex.) Carbon
B. Drawing Lewis Dot Diagrams
Electrons are placed one at a time in a clockwise manner around the symbol in the north, east, south and west positions, ______
______.
Same group # = ______
Ex.)
When it comes to bonding, atoms tend to ______.
o A bond that forms when one atom gives an unpaired electron to another atom is called an ______.
o A bond that forms when atoms share unpaired electrons between each other is called a ______.
C. Writing Lewis Dot Structures for Ions
Uses either 0 or 8 dots, brackets and a superscript charge to designate ion charge
o Ex.) Li1+, Be2+, B3+, C4+, N3-, O2-, F1-
Lewis Dot Diagrams of Ionic Compounds
o Ex.) NaCl
o Ex.) MgF2
Lewis Dot Diagrams (Covalent Compounds)
A. Covalent Lewis Dot Diagrams
A substance made up of atoms which are held together by covalent bonds is a covalent compound.
o They are also called molecules.
Diagrams show bonds in a covalent compound and tells us how the atoms will combine
o Shared e- = ______
o Non-shared e- = ______
Ex.) F2
B. Types of Covalent Bonds
1. Single Bond
a) ______are shared in a bond (___ from each atom)
2. Double Bond
a) ______of e- are shared (_____ total, ______from each atom)
3. Triple Bond
a) ______of e- are shared (_____ total, ______from each atom)
C. Rules for Drawing Lewis Dot Diagrams
1. Add up the total number of valence e- for each atom in the molecule.
a. Each (-) sign counts as 1 electron added to the total, each (+) sign subtracts one electron from the total.
2. Write the symbol for the central atom, then use one pair of electrons to form bonds between the central atom and the remaining atoms.
3. Count the number of electrons remaining and distribute to the surrounding atoms according to the octet rule (or the duet rule for hydrogen).
4. If there are not enough pairs, make sure the most electronegative elements are satisfied. Then, start shifting pairs into double bonds and triple bonds to satisfy the octet rule.
5. If there are extra electrons, stick them on the central atom.
*****But Remember....The Structure MUST Have: the right number of atoms for each element, the right number of electrons, the right overall charge, and 8 electrons around each atom (ideally)*****
Examples
F2 NH3
Examples (cont.)
H2O NH4+
CO2 NO3-
VSEPR: Shapes of Molecules
A. VSEPR Theory (definition)
B. Using the VSEPR Model
o Electron Pair
Any two valence e- around an atom that repel other e- pairs
o Lone pair e- = ______
o Shared e- pair = ______
o Can be single e- pair, two e- pairs together (double bond), or three e- pairs together (triple bond)
C. Basic Shapes and Bond Angles
Total # ofe- Pairs / # of Bonded e- Pairs / # of Unshared (Lone) Pairs / Molecular Shape / Bond Angles / Ex.
1
2
3
4
****See VSEPR handout for shapes of all of the molecular geometry options!!!!
D. Examples: What shape would the following compounds have according to VSEPR Theory?
CH4 CO2
***Draw the Lewis dot diagram for the molecule then determine its VSEPR shape based on the number of total pairs – shared and unshared.
Bond and Molecule Polarity
A. Polar Bond
B. Non-polar Bond
C. Predicting Bond Polarity
o Calculate the electronegativity difference between the Pauling electronegativity values for the 2 elements involved in the bond
Type of Bond / IONIC / CovalentPOLAR / NON-POLAR
Types of Atoms
Electronegativity Difference
0 – 0.4 è Non-polar covalent bond
0.4 – 1.7 è Polar covalent bond (more e/n element has greater pull)
1.7 and up è Ionic bond (electrons are transferred between atoms)
D. Polar Molecules (dipole)
o
o In other words, molecules are polar if the pull in any one direction is not balanced out by an equal & opposite pull in the opposite direction
E. Drawing Polar Molecules
F. Rules for Determining the Polarity of a Molecule
o Shape is crucial è determine the ______first!!
o All non-polar bonds = ______
o Polar bonds à see if they cancel each other out
o If they all cancel = ______
o If they are unbalanced = ______
Ex.) Determine if the following molecular are polar or nonpolar.
H2S
F2
H2O
Special Types of Bonding
A. Hydrogen Bonding
o Elements that undergo H-bonding
o Effects on Physical Properties
B. Van der Waals (London Dispersion) Forces
o ______force between the molecules of a substance
o Force of attraction between an instantaneous and induced dipole
Solids
A. Classes of Solids
o Molecular
o Ionic
o Network Covalent
o Metallic
B. Comparison of Solids
Hardness / Malleability / Conductivity / Melting Point / Ease of Phase ChangeMolecular
Ionic
Network Covalent
Metallic