chemistry 103 lecture 11. outline i. ionic compounds (in review) ii. covalent compounds lewis dot...
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Outline
I. Ionic Compounds (in review)
II. Covalent Compounds Lewis Dot Diagrams/Lewis structures Properties predicted Nomenclature Bond Polarity
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
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
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)
Resonance structures for NO3− are
− − −
:O: :O: :O: ║ │ │
N N N
:O : :O: :O: :O : :O: :O:
Resonance Structures
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