Chemistry 103

Lecture 11

Outline

I. Ionic Compounds (in review)

II. Covalent Compounds Lewis Dot Diagrams/Lewis structures Properties predicted Nomenclature Bond Polarity

Ionic vs. Covalent

NaCl (sodium chloride) CH4 (methane)

Nomenclature - Naming Compounds

FIRST QUESTION: IONIC or COVALENT????

IONIC NOMENCLATURE RULES

(Metal + Nonmetal)

Periodic Table and Some Ions

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

6

Learning Check

Select the correct name for each:1. Fe2S3

A) iron sulfide B) iron(II) sulfide C) iron (III) sulfide

2. CuO A) copper oxide B) copper(I) oxide C) copper (II) oxide

Polyatomic Ions

Polyatomic ion An ion formed from a group of atoms (held together by

covalent bonds) through loss or gain of electrons Can be the positive or the negative ion in an ionic

compound

8

Learning Check

Name the following compounds:

A. Ca3(PO4)2 Calcium Phosphate

B. FeBr3 Iron (III) Bromide

C. Al2S3 Aluminum Sulfide

D. MgSO4 Magnesium Sulfate

9

Learning Check

Write the formulas for each of the following:

A. calcium nitrate Ca(NO3)2

B. iron(II) hydroxide Fe(OH)2

C. aluminum carbonate Al2(CO3)3

D. lithium phosphate Li3PO4

Molecules and Covalent Compounds

11

Diatomic Elements

• These elements share electrons to form diatomic, covalent molecules.

Electron-Dot Diagrams (Lewis Structures)

Electron-dot diagrams show

• The order of bonded atoms in a covalent compound.

• The bonding pairs of electrons between atoms.

• The unshared (lone) valence electrons. (nonbonding)

• A central atom with an octet.

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

Multiple Bonds in N2

In nitrogen N2,

• Octets are achieved by sharing three pairs of electrons, which is a triple bond.

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

Lewis Structures continued…

H2O

C2H4

C2H2

Properties of Bonds

Bond Length Distance between 2 nuclei Triple bond < Double Bond < Single Bond

Bond Strength Energy required to separate 2 nuclei Triple bond > Double Bond > Single Bond

Lewis Dot Structures

Example: CO

:C : : : O:

Coordinate Covalent Bonds - bond in which there is an uneven contribution of the shared electron pairs.

Lewis Dot Structures extended As long as all the atoms in your molecule are

satisfied under the octet rule (exception is H with only 2 electrons), then you have an acceptable Lewis Dot Structure.

Not always easy to decide how to position electrons in a molecule to form the “stable 8” configuration for each atom.

Drawing Lewis Structures

Example: SO3

1. Determine the arrangement of the atoms in the molecule. (Symmetry is key - first atom usually is the central atom unless it is an H)

O

S

O O

Drawing Lewis Structures,

continued 2. Determine the total number of valence electrons present.

O

S

O O S = 6 valence electrons O = 6 valence electrons x 3 = 18 TOTAL = 24

Drawing Lewis Structures,

continued… 3. Determine the total number of valence electrons the molecule (or ion) will need to have a noble gas configuration.

Nobel Gas Count H 2 S, O, F, … 8

Drawing Lewis Structures,

continued… 3. Determine the total number of valence electrons the molecule (or ion) will need to have a noble gas configuration.

O

S

O O

Valence count = 24

Noble Gas count = 8 x 4 = 32

Drawing Lewis Structures,

continued… 4. Determine the number of bonding electron pairs needed:Noble Gas count (step 3) - Valence (step 2)

2= Total number of bonds

SO3 32 - 24 = 4 bonds 2

Drawing Lewis Structures,

continued… 5. Write in the skeletal structure, the bonding electron pairs and the nonbonding pairs of electrons to satisfy octet rule.

6. Check the electron dot structure to confirm that the total number of electrons present is the same as the valence count in step 2

THIS ONLY WORKS FOR SYSTEMS THAT FOLLOW THE OCTET RULE - NO EXCEPTIONS!!!!

Resonance Structures

Two or more Lewis Dot structures that have the same arrangement of atoms and the same number of electrons, but differ in the location of the electrons (bonds)

Lewis Dot Structure

Draw the Lewis Dot Structure for Nitrate (NO3

-)

Resonance structures for NO3− are

− − −

:O: :O: :O: ║ │ │

N N N

:O : :O: :O: :O : :O: :O:

Resonance Structures

NOMENCLATURE

Naming covalent compounds

Nomenclature - Naming Compounds

FIRST QUESTION: IONIC or COVALENT????

IONIC RULES COVALENT RULES

(Metal + Nonmetal) (Nonmetals)

Naming Covalent Compounds Covalent Compounds

Greek Prefixes Common Names H-first(BINARY = 2 ELEMENTS)

Naming Binary Covalent Compounds First word of name:

Greek prefix + name of first element Note: if the prefix would be “mono” for the first element,

the prefix is not included Note: when an element name begins with a vowel, an a

or o at the end of the Greek prefix is dropped for phonetic reasons

Second word of name Greek prefix + stem of name of second element

with “-ide” ending

Greek Prefixes

Table in text

1 mono 6 hexa

2 di 7 hepta

3 tri 8 octa

4 tetra 9 nona

5 penta 10 deca

Naming Covalent Compounds Examples:

P4O10

CO

CO2

NCl3

N2O5

Naming Covalent Compounds Covalent Compounds

Greek Prefixes Common Names H-first

Common Names

H2O water

H2O2 hydrogen peroxide

CH4 methane

NH3 ammonia

PH3 phosphine

Naming Covalent Compounds Covalent Compounds

Greek Prefixes Common Names H-first

Hydrogen First in compound

HCl hydrogen chloride H2SO4 hydrogen sulfate

H3PO4 hydrogen phosphate

When in water (aq) has very different properties – ACIDS

HCl(aq) hydrochloric acid

H2SO4(aq) Sulfuric Acid

H3PO4(aq) Phosphoric Acid