Dublin High School • Chemistry

Smells:

ovalent Com Let's Build It! - Prelab

Introduction: (Complete in your lab notebook) 1) Describe IN YOUR OWN WORDS what a molecular formula is: 2) Describe IN YOUR OWN WORDS what a structural formula is: 3) How are molecular formulas and structural formulas similar? 4) How are molecular formulas and molecular structures different? 5) Describe what each part of the model represents: (1) the wooden balls, (2) the wooden sticks, (3) the springs, and (4) the number of holes. 6) What is the one exception to the relationship between holes and bonds in our molecular models? How will you deal with this? (Look at Table 1) 7) What is the purpose of this lab? 8) What three structures will you be making in step 2? 9) What four structures will you be making in step 3? 10) What four structures will you be making in step 4? (What are the formulas?) 11) What does the hint say about carbon (C) in step 6? 12) What structure will you be constructing in step 5? What is "urea"? 13) In step 6, how is a "structural isomer" defined in general? (Not just about butane, but in general.) 14) Do isomers have the same physical and chemical properties?

Let's Build It! Lab Instructions Introduction A molecule can be represented on paper by either a molecular or a structural formula. A molecular formula indicates the number and kind of each atom present in a molecule. Some familiar molecular formulas are shown below. CH4 NH3 H20 These molecular formulas do not provide any information concerning the actual arrangement of atoms in a molecule. Such information is given by structural formulas such as the following. H

I I

H-C-H

H-N-H

H

H

H-O-H

I

These structural formulas are two-dimensional. The angles shown are not true to the shape of the molecule. Structural formulas can be made to convey more information by indicating the effect lone pairs of electrons have on the overall shape of the molecule. Lone pairs take up more space around an atom than bonded pairs resulting in the bonded pairs being "pushed" closer together. To convey the molecular shape, structural formulas can be redrawn in the following fashion:

__.....0...__ H

H H In this lab activity, you will construct three-dimensional models to help you visualize the shapes of molecules. You will use ball-and-stick models, in which colored balls represent atoms and short gray plastic sticks represent the bonds. Double and triple bonds are represented by the longer and thinner gray plastic sticks. The plastic colored balls have holes to accept the gray plastic sticks. The number of holes in the ball represents the maximum number of bonds that a given atom can have. The balls are also color-coated as indicated in Table 1 so that atoms of different elements can be distinguished.

Table 1 Atom Hydrogen Carbon Oxygen Nitrogen Haloqen Sulfur Phosphorous •

Symbol

Color of ball

Electron Domains

H

White Black Red Blue Green Yellow Purple

4 6 3 1 6 3

c

0 N F, Cl, Br, I

s

p

1

Maximum# of bonding locations 1 4 2 3 1 6 3

Not all the holes in each atom will necessarily be used in the model of a particular compound.

Let's Build It! Lab Instructions Purpose

The purpose of this activity is to construct molecular models, using a ball-and stick model set and to create Lewis dot structures as guides for building these molecules. Students will gain practice in describing the shapes of the molecules that they build. Student will also practice recognizing organic functional groups and relate those functional groups to "smells."

Procedure

1. For the molecules listed in Table 1, write the molecular formula, structural formula, Lewis Dot structure, Ball-and-Stick model and the shape of each of the given molecules. 2. For the molecules listed in Table 2, write the molecular formula (if not already given), structural formula, Lewis Dot Structure and the name of the functional group in each of the different molecule. 3. Construct a model of butane,

~H 10 •

(Hint: The carbons are bonded to one another in a continuous,

unbranched chain.) Draw a sketch of this molecule in your laboratory notebook. Can you construct a model of a different molecule having the same molecular formula as butane? Make a model of such a molecule and sketch its structure in your laboratory notebook. Hint: The two different compounds having the molecular formula

~H 10

are called structural isomers. They have identical molecular

formulas, but different structural formulas. They also have different physical and chemical properties. 4. Complete the Post-lab Questions in your laboratory notebook.

Let's Build It! Data Table Data Table 2 Molecule

Ethene

Molecular Formula

CaH4

. Ethyne

CaH2

Ethane

CaH&

Methanol

CH,OH

Methyl Methanoate

CaH40z

Acetone or Dimethyl

c,H.o

Ketone

Dimethyl Ether

C,HoO

Methylamine

CHsN

Methanoic

CzH40z

Acid

Methyl Bromide

CH,Br

Structural Formula

Lewis Dot Structure

Ball-and-Stick Model

Functional Group

Dublin High School • Honors Chemistry

Smells·

valent Co

d Let's Build It! Data Table

Data Table 1 Molecule

Molecular Formula

Hydrogen Cyanide

Boron Trifluoride

Sulfur Difluoride

Silicon Tetrabromide

Phosphorous Trichloride

Phosphorous Pentachloride

Sulfur Hexabromide

Oxygen

Benzene

C&H&

Structural Formula

Lewis Dot Structure

Ball-and-Stick Model

Shape