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

Package

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

1. Add up total number of valence e- 2. Pick central atom and create the bonds3. Surround the adjacent atoms.4. Put extra electrons on the central atom.5. 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!

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 6- hexa

2- di 7- hepta

3- tri 8- octa

4- tetra 9- nona

5- penta 10- deca

Examples: NO

SiCl4

Practice

Formulas to names

1. SO3

2. ICl33. 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 and Pi bonds

• Sigma ( bonds are single bonds

• Pi ( 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?

t

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)

Oxyacids-Acids containing H,O, and a Nonmetal.

(Polyatomic ion)

If the poly ends in ate-

change the end to ic and add “acid”

H3PO4

If the poly ends in ite-

change 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