Bonding and Moles unit

Questions:
1.) What properties in general do covalent-bonded substances have? Describe at least four properties based on
information from your experiment. See your data table.

a.
b.
c.
d.
2.) What general properties do ionic-bonded substances have? Describe at least four properties based on
information from your experiment. See your data table.
a.
b.
c.
d.
3.) Which compound melted most easily-salt or sugar? Explain why one melts easily and the other does not
melt at all.

4.) Using the Periodic Table explain how the position of the elements that make up sugar (the formula for sugar
is C12H22O6 and Ethanol is C2H5OH) can be used to tell if the bonds are ionic or covalent. (HINT: ionic
compounds are made of a metal plus a non-metal; covalent compounds are made of non-metals combined with
other non-metals)

5.) Using the Periodic Table explain how the position of the elements that make up the salts (NaCl, CaCl2 and
KCl) can be used to tell if the bonds are ionic or covalent. (HINT: ionic compounds are made up of two or more
elements that are far apart on the Periodic Table)

51

Dot
 Structures
 and
 Molecular
 Model
 Building
 Lab
 

Purpose - To investigate the three-dimensional shapes of molecules by building molecular
models.

Introduction
You can represent a molecule on paper with either a molecular formula or a structural formula.
However, molecular formulas, such as NH3, provide no information concerning the actual
arrangement of atoms in the molecule. Structural formulas give some information about the
arrangement of atoms in the molecule.
However, structural formulas provide only limited information because they are two-
dimensional. Actual molecular shapes are three-dimensional. A molecular model is far superior
to a structural formula when it comes to visualizing atomic arrangement. Compared to
molecular formulas and structural formulas, molecular models provide much more information
about the true shapes of the molecules.

Example: NBr3 1) Max e- 32
1) The max. # of electrons is equal to 32 (8×4 = 32) 2) Valence e- 26
3) Bonding e- 6
2) The # valence electrons is 5 for N, and 3×7 = 21 for
4) Bonds 3
the 3 Br atoms; 5 + 21 = 26 valence electrons

3) The # of bonding electrons is equal to the maximum electrons 5) Nonbonding e- 20

minus the valence electrons, (32 – 26 = 6).

4) The # of bonds is equal to the # of bonding electrons divided by 6) Nonbonding pairs 10
two (6/2 = 3), because there are two electrons per bond. As a result,

the # of bonds is 3.

5) If we arrange the molecule so that the atoms are held together by three bonds (3 single

bonds).
6) The number of nonbonding e- = the # of valence electrons minus the # of bonding electrons,
26 - 6 = 20. The number of nonbonding pairs of e- is 20/2 = 10.

In this experiment, you will use ball-and-stick models to help you visualize the shapes of
molecules. The balls are color-coded and sized to represent different atoms. The balls are also
drilled with holes to accept sticks and springs; the number of holes in a ball reflects the
maximum number of bonds a given atom can form. Single bonds are represented by short
wooden sticks; double and triple bonds are represented by two or three springs.

Procedure
1. Dot Structures – In the table, draw dot structures for the following compounds/ions – H2O,
NH3, CH4, CCl4, CCl2F2, HCN, CO(NH2)2, C4H10, SO2, PCl3, SF2, and N2.
2. Using the ball-and-stick model set, construct models of the molecules above. Take a picture
of each model being sure to label the model with the formula of the molecule.
3. Calculate the ΔEN of each bond using the electronegativity values from your periodic table.
Always subtract the lesser number from the greater number to be sure the answer is a positive

52

number, and then decide if the overall molecule is polar or nonpolar. Remember, for a

molecule to be polar, it must have polar bonds AND be asymmetric. See 8.4 notes.

Name _____________________________
Draw the dot structures below the formula. Use pencil in case you have to redo any of them.
The instructor must check all before you can move on to the models.

H2O NH3 CH4

CCl4 CCl2F2 HCN

CO(NH2)2 C4H10 SO2
SF2 N2
O
HNCNH

HH

PCl3

53

Data Analysis Table

Molecule/ion Bond ΔEN Polar/Nonpolar?
H2O O−H 3.44-2.20 = 1.24 Polar molecule
NH3 N−H
CH4 C−H
CCl4 C−Cl
C−Cl
CCl2F2 C−F
H-C
HCN C-N
C−O
CO(NH2)2 C−N
N−H
C4H10 C−H
SO2 S−O
PCl3 P−Cl
SF2 S−F
N2 N−N

Conclusion
What do the polar molecules have in common?

What do the nonpolar molecules with polar bonds have in common?


 

 

54

Moles,
 atoms,
 grams
 oh
 my!
 Lab
 

GOAL: To understand the concept of a mole and to calculate mole ↔ gram ↔ atom/molecules conversions.
OBJECTIVES:

• Measure out in grams of in various substances and calculate the amount of moles.
• Calculate the amount of atoms in various substances.
Materials for each group
• Electronic balance
• Three capped test tubes labeled “NaCl”, “water”, and “ammonium sulfate” and filled with the

corresponding substances. (One at each station)
• Spatula for dispensing chemicals
• plastic pipettes to use with the water. (One at each station)
• Empty colorless/clear plastic cup, red plastic cup, and blue plastic cup - Labeled with you group

number.
• Take your lab calculation sheet and proceed with your activity. You must go up to the instructor’s desk

after each task to check for accuracy.
Procedure:

Take your lab sheet and proceed with the instruction on it. Remember that you must go up to the
instructor’s desk after each task to check for accuracy.

55

Group #__

Group members: ________________________________________________________________________
Complete task A through E, but you must go up to the instructor’s desk after each test to check for accuracy.
You will be awarded points based on your accuracy. Your group will be allowed one “do-over”. YOU MAY
NOT ask other groups for help. If so, you will be disqualified and will receive a zero for the lab.
Use the sheet for your group and measure the amount for your group. When you have completed the task, bring
the cup to me for checking. Remember, the cup has mass too!
Each task that you complete within 2% of the correct answer, you will receive 8 points. If you complete the
task within 5% of the correct answer, you will receive 6 points, and if you are within 10% accuracy, you will
receive 4 points for the task. Any measurement above 10% error will only receive 2 points for trying. You will
get one “do over” in the entire lab. You MUST show all work AND UNITS for each calculation.

A. Measure out ______________________ moles of salt (NaCl) into a clear, dry cup.

Show work:

B. Put _______________________ molecules of water into a red dry cup.

Show work:

C. Obtain a sample of copper metal from your teacher. Determine how many atoms it contains. Show your
work and bring the sample to teacher to check for accuracy.

Show work:

D. Measure out and check for accuracy with your instructor _________________ atoms of aluminum.

Show work:

E. Measure out ______________________ moles of ammonium sulfate into a blue, dry cup.

Show work:

56

Mole
 conversions
 summary
 sheet
 

All mole conversions work on the principle that one mole is equal to all of the following quantities:
6.02×1023 representative particles (u) = 22.4L of gas (at STP) = molar mass (g)

Because of this, you can convert between any two quantities using H × W = W
H

particles to moles moles to particles
moles to volume of gas (L)
3.5molAu × 6.02 × 1023atomsAu = 2.1× 1024 atomsAu
moles to mass (g) 1molAu

volume of gas (L) to moles

6.34 LNO2 × 1molNO2 = 0.283molNO2
22.4 LN2O4

mass (g) to moles

particles to mass (g) mass (g) to particles

4.05 × 1021uH2O × 18.0 gH 2O = 0.121gH 2O 40.0gNaCl × 6.02 × 1023uNaCl = 4.12 × 1023uNaCl
6.02 × 1023uH2O 58.5gNaCl

particles to volume of gas (L) volume of gas (L) to particles

4.57 × 1023uH2 × 22.4 LH2 = 17.0LH2 86.3LN2O4 × 6.02 × 1023uN2O4 = 2.33 × 1024 uN2O4
6.02 × 1023uH2 22.4 LN2O4

mass (g) to volume of gas (L) volume of gas (L) to mass (g)

63.5gSO2 × 22.4 LSO2 = 22.2 LSO2
64.1gSO2

When given a formula Percent Composition
When given experimental data

Empirical Formula

(Ex. – What is the empirical formula with a composition by mass of 17.5 g N and 3.75 g H?)

17.5gN × 1molN = 1.25molN / 1.25 = 1molN
14.0gN
NH3
3.75gH × 1molH = 3.75molH /1.25 = 3molN
1.0gH

57

Unit
 Test
 Setup
 

20 matching on the vocabulary (7 from chapter 7, 7 from chapter 8, and 6 from chapter 10)
20 multiple choice on the objectives (6 from chapter 7, 7 from chapter 8, and 7 from chapter 10)

Short Answer – Complete any two.

Write the formulas obtained when each of these atoms loses or gains valence electrons and becomes an ion. Tell whether
each is a cation or an anion.

a. Cl b. Na c. Be

Write the electron dot structures for each of the following atom-ion pairs.

Atom Ion

a. Na, Na ion
b. Cl, Cl ion
c. P, P ion

The following covalent molecules have only single covalent bonds. Draw an electron dot structure for each one.

a. HBr b. PCl3 c. H2O2

The polymer used for the nonstick surface of cooking utensils is 24.0% C and 76.0% F by mass. What is the empirical
formula of this polymer?

Essay – Complete any two.

Use electron dot structures to predict the structure of the ionic compound composed of aluminum and chlorine.

Explain the difference between a nonpolar covalent bond, a polar covalent bond, and an ionic bond. Use electronegativity
to explain the differences.

Explain how the mass of a single atom in an element (in amu), the mass of one mole of atoms of that element, and
Avogadro’s number are related.

If you have 3.53 moles of carbon monoxide, calculate the number of molecules, the mass (g), the volume at STP (L), and
the total number of atoms.


 

 

58

Unit
 Review
 Materials
 

Chapter
 7
 vocabulary
 review
 

Match the correct vocabulary term to each numbered statement. Write the letter of the correct term on the line.

Column A Column B

1. compounds composed of cations and anions a. chemical formula
2. the attraction of free-floating valence electrons for b. valence electrons
c. electron dot structure
positively charged metal ions d. octet rule
3. the lowest whole-number ratio of ions in an ionic e. halide ion
f. formula unit
compound g. ionic bonds
4. the electrostatic attraction that binds oppositely charged h. coordination number
i. metallic bonds
ions together j. ionic compounds
___h____ 5. the number of ions of opposite charge that surround the k. alloy
l. anions
ion in a crystal m. cations
6. negatively charged ions
7. shows the kinds and numbers of atoms in the smallest

representative unit of a substance
8. a diagram that shows valence electrons as dots
9. a negative ion formed when a halogen atom gains an

electron
10. In forming compounds, atoms tend to react so as to

acquire the stable electron configuration of a noble gas.
11. electrons in the highest occupied energy level of an

element’s atoms.
12. a mixture of two or more elements, at least one of which

is a metal
13. positively charged ions

59

Chapter
 10
 vocabulary
 review
 

Select the term from the following list that best matches each description.

mole percent composition
Avogadro’s number empirical formula
molar mass standard temperature and pressure (0° C, 1 atm)
22.4 L

1. a description of the relative amounts of each element in a compound

2. the lowest whole-number ratio of the atoms of the elements in a compound

3. the volume occupied by one mole of any gas at STP

4. the mass (in grams) of one mole of a compound

5. the SI unit representing 6.02 × 1023 representative particles of a substance

6. 6.02 × 1023 particles

7. the temperature and pressure at which one mole of gas occupies a volume of 22.4 L


 

 

60

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Chapter 8
62

Chapter 10
63