Module 8

Question 1

Counting valence electrons in a molecule

Answer 1

1. Count valence electrons on each atom
2. Add them up
3. If molecule/polyatomic ion has a charge, add electrons based on the charge

Question 2

Valence Shell Expansion Exception

Answer 2

“Atoms of elements in Period 3 and higher can sometimes fit more than 4 pairs of valence electrons around them.”

Question 3

Draw SF6
(Include lone pairs)

Answer 3

Valence Shell Expansion
Molecule should have:
6 bonds
3 lone pairs on every F atom
S is the central atom

Question 4

Draw XeF4
(Include lone pairs)

Answer 4

Valence Shell Expansion
Molecule should have:
4 bonds
3 lone pairs on every F atom
Xe should have 4 bonds PLUS 2 lone pairs

Question 5

When is a Lewis structure reasonable?

Answer 5

It passes:
Test 1: Each atom has the correct number of valence electrons
Test 2: It passes the octet rule (with exceptions).

Question 6

Finding Ionic/Covalent Character of a Molecule/Ion

Answer 6

1. Subtract the electronegativity of one atom of an element against the other. (This the electronegativity difference.)
2. Determine if w.in these ranges:
   <0.5 – Covalent non-polar
   0.5-2.0 – Covalent polar
   >2.0 – Ionic

Question 7

Exceptions to the Octet Rule

Answer 7

1. Valence shell expansion
2. Electron deficient molecules (not enough elecrons to give)
3. Odd electron exception (molecule has odd-numbered electrons, thus needs a place to put single electron. happens in Periods 2 and 3)

Question 8

methyl

Answer 8

chemical group
-CH3

Question 9

methylene

Answer 9

chemical group
-CH2-

Question 10

hydroxy

Answer 10

chemical group
-OH

Question 11

carbonyl

Answer 11

chemical group
-CO-

Question 12

amino

Answer 12

chemical group
-NH2