Pre-Activity Problem Set: Activity 6a
Score:
Name:
pts
1) What is a covalent bond? How is a covalent bond like peanut butter between two slices of
bread?
2) What is a molecule?
.^.0™PJ5.te_t_n? !r.^wJs dot symbols for the following elements:
a)
-----~j~ c )'~"
C
^
O
i
i
i
j
.-.,--.--.
N
i
i
F
4) Indicate which electrons are shared as bonds and which electrons are the nonbonding lone
pair(s) in the following drawings:
,
____
H:"F":
• •
i
H:'O':H
••
.........
5) Distinguish between theLsjna.le_, double, and triple bonds in the following molecules:
„
..
H-C^C—H
H—C—O—H
• •
6) Look at the puzzle pieces on the next four pages (don't forget to cut them out before
class). What factor determines how many dots are on each puzzle piece?
Explorations in Conceptual Chemistry: Activity 6a
157
Lewis dot puzzle pieces (page 1)
C
c
S
^
Explorations in Conceptual Chemistry: Activity 6a
159
^
Lewis dot puzzle pieces (page 2)
Explorations in Conceptual Chemistry: Activity 6a
161
Lewis dot puzzle pieces (page 3)
-
N
N
N
N
Explorations in Conceptual Chemistry: Activity 6a
163
~
Lewis dot puzzle pieces (page 4)
O
Explorations in Conceptual Chemistry: Activity 6a
165
'
Part A\s dot structures (for molecules with single bonds)
Instructions: Working in pairs, use the puzzle pieces you cut out to build, one at a time, the
Lewis dot structures for the covalent molecules below. In each of these compounds only one
pair of electrons is shared by any two atoms (this is called a "single bond"). The remaining
electrons are called "nonbonding lone pairs" or "unpaired electrons".
Questions: From your completed puzzle, draw what each molecule looks like by replacing each
pair of shared electrons with a line (bond). Use the HF example below as a guide.
becomes:
Example: HF
H-F:
NH3
H3CCH3
CH2CIBr
H2S
(usually written C2H6)
..
CH4
H20
PH3
H2NNH2
^
Explorations in Conceptual Chemistry: Activity 6a
(usually written N2H4)
Instructions'. When the class is done with Part A, your instructor will have students draw each
of the final molecules on the board. You will use these sample molecules to determine some of
the rules governing the formation of covalent compounds.
Questions:
1) How many bonds does C typically form?
2) Does the answer to question 1 make sense based on the number of valence electrons that C
needs to share to obtain a full valence shell? Explain.
3) How many bonds does N typically form?
4) Does the answer to question 3 make sense based on the number of valence electrons that N
needs to share to obtain a full valence shell? Explain.
5) How many bonds does O typically form?
6) Does the answer to question 5 make sense based on the number of valence electrons that O
needs to share to obtain a full valence shell? Explain.
7) How many bonds do H, F, C\, and Br typically form?
8) Does the answer to question 7 make sense based on the number of valence electrons that H,
F, C\, and Br need to share to obtain full valence shells? Explain.
9) Based on your answer to question 7, explain why H, F, C\, and Br are most likely to be end
(terminal) atoms rather than central (bridging) atoms in a molecule.
168
Explorations in Conceptual Chemistry: Activity 6a
Part B'. Lewis dot structures (for molecules with double and triple bonds)
Instructions: Working in pairs, use the puzzle pieces you cut out to build, one at a time, the
Lewis dot structures for the covalent molecules below. In each of these compounds, two pairs
(a "double bond") or even three pairs (a "triple bond") of electrons may be shared between any
two atoms.
Questions: From your completed puzzle, draw what each molecule looks like by replacing each
pair of shared electrons with a line (bond). If two atoms share four electrons, then draw two
lines (double bond). Use the O2 example as a guide.
Example:
becomes:
0=0
• •
HCICCHCI
(usually written C2H2CI2)
• •
N2
"
HCN
HNNH
H2CCH;
(usually written N2H2)
(usually written C2H4)
HCOOH
Explorations in Conceptual Chemistry: Activity 6a
169
Instructions: When the class is done with Part B, your instructor will have students draw each
of the final molecules on the board. You will use these sample molecules to determine some of
the rules governing the formation of covalent compounds.
Questions:
1) If a "double bond" counts as two bonds and a "triple bond" counts as three bonds, do these
compounds all follow the rules you determined from the molecules in Part A? Explain.
2) In summary, what is the typical number of bonds that each of the following elements ends
up with in a covalent compound?
a. nonmetal elements in group 14 (C, Si)
b. nonmetal elements in group 15 (N, P, As)
c.
nonmetal elements in group 16 (O, 5, Se, Te)
d. hydrogen and elements in group 17 (H and F, C\ Br, I)
170
Explorations in Conceptual Chemistry: Activity 6a