Chemical Bonding
Chapter 6
Covalent Compounds
Nonmetal bonding with another nonmetal
Electronegativity difference less than 1.7
Electrons being shared
Draw the MO diagram for
Chlorine and Hydrogen…
Diatomic Molecules
You must memorize these!!
H2 N2 O2 F2 Cl2 Br2
I2
(At2)
Magnificent 7—
I won’t hold you responsible for astatine, just
know that trends in a group apply!
Formation of Covalent Bond
Bond stability
Octet Rule
• Noble gases: have filled valence shells =
2 (He) or 8 e• Octet Rule tells us that chemical
compounds tend to form so that atoms
obtain an octet of e- in its highest energy
level.
Visual Concepts
Exceptions
• Boron trifluoride BF3
• PF5 and SF6 can expand the shell and
share more electrons. (10 and 12
respectively)
Electron – Dot Notation
• Dots are used to represent valence electrons around
an atom.
• Visual Concepts
Lewis Structure Rules
Add up total number of valence ePick central atom and create the bonds
Surround the adjacent atoms.
Put extra electrons on the central atom.
Beg, borrow or steal so that all the atoms are
stable (have a complete octet).
6. Make sure the number of valence e- you
started with are the number you used!
1.
2.
3.
4.
5.
Lets do…
CH4
SiF4
NCl3
Forming Multiple Bonds
CO2
N2O
Warm Up
Draw the Lewis Structure for CS2
Circle each atom showing a complete octet.
Exceptions
• Boron trifluoride BF3
• PF5 and SF6 can expand the shell and
share more electrons. (10 and 12
respectively)
Let’s talk about your WS
Remind me to talk about the polyatomic
ions!!
Let’s add some Dipoles!
Polyatomic ions
Examples
Naming Covalent Compounds
Covalent compounds are molecules or
molecular compounds…
Indicate the number of each atom using
prefixes…..
…change the end of the name to “ide”
Covalent Prefixes
Use the prefixes!
1- mono
2- di
3- tri
4- tetra
5- penta
Examples: NO
SiCl4
6- hexa
7- hepta
8- octa
9- nona
10- deca
Practice
Formulas to names
1. SO3
2. ICl3
3. PBr5
4. CO
5. CO2
Names to formulas
1. Carbon tetrachloride
2. Dinitrogen monoxide
3. Dinitrogen tetroxide
4. Phosphorus triiodide
5. Sulfur heptafluoride
Homework…
Name all the molecular compounds on the
Lewis Structure WS….
Remember to get your ions names from the
polyatomic ion sheet!
Multiple Covalent Bonds
• Bond length and strength
– Triple bonds are the shortest (pm) and have
the most Energy (kJ/mol)
– Single bonds are the longest (pm) and have
the least amount of Energy (kJ/mol)
Sigma s and Pi p bonds
• Sigma (s) bonds are single bonds
• Pi (p) bonds are the bonds that follow in a
multiple bond situation
Resonance Structures
• Some molecules cannot be correctly
identified by a single Lewis structure
• When you can draw two mirror images,
you probably have a resonance structure
– For example: Ozone O3
Visual Concepts
Draw the Resonance Structures for
Silicon Trioxide
Ionic vs covalent
Visual Concepts
Properties of Covalent
Compounds
– low melting point
– low boiling point
– many are gas and liquid at room temp
– typically do not conduct electricity when
dissolved in water
This is due to the fact that forces of attraction
between molecules are much weaker when the
electrons are being shared.
Conductivity Demo
Types of Bonds Lab
Pre-lab- 8 minutes
1. Make a list of the characteristics of
ionic and covalent compounds.
2. Discuss what makes the
compounds different.
Purpose- To classify 3 unknown samples as
being either ionic of molecular using the
known characteristics.
Procedure: Design an experiment that
would help you identify if an unknown
sample is ionic or covalent.
Would it be helpful to test your known compounds
and compare results?
Materials Available
Equipment
Bunsen Burner
Ring Stand
Wire holder
Test tubes
Test tube racks
Conductivity meter
Chemicals
Distilled water
Sodium Chloride
Sugar (C6H12O6)
Unknown 1
Unknown 2
Unknown 3
Warm Up
Determine if the following are ionic or
covalent… name them correctly.
CF4
NaCl
CoF2
SO2
Would they be considered molecules or
formula units?
Naming Acids
Acids are molecular compounds that have
hydrogen atoms…
Binary Acids- have 2 elements
HCl- Hydrochloric Acid
Oxyacids- Acids containing H,O, and a
Nonmetal. (Polyatomic ion)
OxyacidsAcids containing H,O, and a Nonmetal.
(Polyatomic ion)
If the poly ends in atechange the end to ic and add “acid”
H3PO4
If the poly ends in itechange the end to “ous” and add “acid”
HNO2
Metallic Bonding
d-orbital electrons
• This is an extremely strong bond
Gives metal: luster, malleability, ductility,
conduct electricity and heat
Metals
Share a sea of electrons…
Explains why so many of them are good
conductors of electricity.
Alloys
• Combination of metals
– Bronze: copper and tin
– Brass: zinc and copper
– Coin metal: copper and nickel
– Solder: lead and tin
Substitutional Alloy
• Some of the main metal atoms are
replaced by other metal atoms of similar
size. An example is brass where one-third
of the atoms of the host copper are
replaced with zinc atoms.
Interstitial Alloy
• Formed when some of the holes in the
closest packed metal structure are
occupied by small atoms.
• Steel is an interstitial alloy, containing
carbon atoms in the holes of an iron
crystal.
Stainless steel is a substitutional/interstitial alloy