10/8/2014

Today:

◦ Lewis Dot Structures:
 Following Octet Rule
 Drawing & Recognizing Correct
Lewis Dot Structures
 Bonding & Lone Pair e Double & Triple Bonds
Complete Course Survey by at
at 11 pm for BONUS POINTS
◦ Nomenclature
Diatomic Molecules:
Understanding why certain elements pair up
OCTECT RULE:
Each atom shares enough electrons with its neighboring atoms to
arrive at a noble gas configuration with 8 ELECTRONS
• Write the Lewis Dot Structures for diatomic chlorine gas, oxygen
gas, & nitrogen gas
Electron orbitals overlap on adjacent atoms to share
electrons and reach a STABLE noble gas configuration
Bonding vs. NON-Bonding Electron Pairs:
+
+
• Bonding Electrons: 2 electrons SHARED between atoms
written as a single line
• Lone Pair Electrons: reside exclusively on one atom,
NOT shared between atoms
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10/8/2014
Predicting the Formula of Covalent Molecules with Lewis Theory
Using only the concepts of Lewis Bonding Theory:
Predict the likely covalent molecule that would form
between Phosphorus & Chlorine.
A. PCl
B. PCl2
C. PCl3
Hint: They may combine in any ratio as
needed so that each atom arrives at a
COMPLETE OCTET (through mutually
sharing electrons with neighboring atoms).
D. P3Cl
E. P2Cl3
Lewis Dot Structures for More Complex Molecules:
H
H
C
H
H
• Write the Lewis Dot Structure for Carbon Dioxide.
Lewis Dot Structures for Neutral Molecules:
A Systematic Approach to Predict Bonding Arrangements
6.
If needed, move lone pairs from outer atoms to bond with the
central atom to form an octet on the central atom.
 This will make double or triple bonds.
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10/8/2014
Electronegativity: Measuring an element’s pull on electrons
Ionic Bonds form between elements with a large difference in electronegativities:
• …typically when METALS combine with NON-METALS
Covalent Bonds occur between elements with similar electronegativities:
• …when NON-METALS bond with other NON-METALS
Table of Electronegativities
Examples:
CO
CH2O
ClF3
In an industrial accident, a spill of 900 kg of chlorine trifluoride BURNED
through 12 inches of concrete & almost 3 feet of gravel beneath!
Writing the Lewis Dot Structure for Polyatomic Ions
How many TOTAL electrons would be involved in bonding
in the polyatomic anion, NITRATE: NO3- ?
A. 11 electrons
B. 12 electrons
C. 22 electrons
D. 23 electrons
E. 24 electrons
Polyatomic Ions are just
CHARGED molecules
 For each negative (-) charge:
add one electron.
 For each positive (+) charge:
subtract one electron.
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10/8/2014
Lewis Dot Structures for Polyatomic Ions:


6.
For each negative (-) charge: add one electron.
For each positive (+) charge: subtract one electron.
If needed, move lone pairs from outer atoms to bond with the
central atom to form an octet on the central atom.
 This will make double or triple bonds.
CO32-
Examples:
NH4+
NO2BF4-
Recognizing CORRECT & INCORRECT Lewis Dot Structures
Select the Lewis Dot Structures below that are VALID.
A.
B.
C.
D. ALL of these Lewis Dot Structures are VALID
E. NONE of these Lewis Dot Structures are VALID
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10/8/2014
Sapir–Whorf hypothesis: a principle of linguistic
relativity that holds that the structure of a language
affects the ways in which its speakers conceptualize
their world.
Sami people, who live in the northern tips of Scandinavia
and Russia, use at least 180 words to describe snow and
ice (according to Ole Henrik Magga, a linguist of Norway)
Nomenclature:
A systematic language for describing the
regularity and bonding patterns found in chemical
substances
Names and Formulas for
BINARY Molecular COVALENT Compounds

Binary molecular compounds are composed of two
non-metals.

The ratios in which they combine are not as
predictable as they are for IONIC compounds.

For example, C and H can form compounds with
many different formulas, including CH4, C3H8,
C50H102.
Formulas & Naming: Binary Covalent Compounds
Rules for naming molecular compounds:
1. The first element in the formula is named by its name on
the periodic table.
2. The second element is named as it would be if it were
the anion of the element. (Though it is not the anion!)
3. Use prefixes to indicate how many of each element is
present.
Exception: If only one of the FIRST element in the
formula is present, do NOT use the prefix mono-. Just
leave it off.
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10/8/2014
Binary Covalent Compounds – Examples

Write the name or formula:
1.
CO
2.
CO2
3.
N2O5
4.
N2O
5.
NO2
6.
P4O10
7.
Sulfur trichloride
8.
Oxygen difluoride
9.
Disulfur trioxide
Prefixes for Naming Covalent compounds:
# of atoms of element
Prefix
1
mono-
Commit prefixes
1-10 to memory
2
di-
3
tri-
4
tetra-
5
penta-
6
hexa-
7
hepta-
8
octa-
9
nona-
10
deca-
11
undeca-
12
dodeca-
6