Worksheet

Atoms Under the Wheels: Modeling a Skate Park

Grade 7 physical science: use model-kit rules and a viewer app to model wax and water molecules and the networks in quartz, grip-tape grit and steel.

Grade 7ScienceInteractive · Printable

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Single worksheet
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1 NGSS standard
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10 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Short answer

About this worksheet

What students practice

Students use model-kit rules to build and count atoms in simple molecules and long-chain molecules.
Students work out the atom ratio and formula of an extended structure from how its atoms are joined.
Students tell molecules from extended structures using descriptions of atomic models.

How to use

If a model kit is available, let students build water and a short wax chain before Section 1. For Section 2, have them sketch a few joined atoms to see how each oxygen is shared.

Curriculum

NGSS standard covered

MS-PS1-1

Model the atoms in simple molecules and in extended structures such as crystals.

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Atoms Under the Wheels: Modeling a Skate Park

Build models of wax and water, then work out the formulas of the networks in sand, grit and steel.

Molecules from the model kit

Read the passage, then answer the questions.

Modeling the Makeover

1The Westbrook skate park is getting a makeover, and the city asked teens from the park's skate club to help on work days. Volunteer coordinator Ms. Fenna de Vries, who works as a chemist, brought along a molecule model kit and a tablet with a model viewer app. She challenged skaters Mateus Oliveira and Keziah Thorne to model the materials around them, from the wax on the ledges to the concrete in the bowl. This month the crew is patching the concrete bowl, putting in a new steel rail and sticking fresh grip tape on the club's loaner boards. On every work day, the skaters also fill a cooler with ice and water bottles.

2In the kit, black balls stand for carbon (C) atoms, white balls for hydrogen (H), red balls for oxygen (O) and gray balls for silicon (Si). Each rod stands for a bond that joins two atoms. Every ball has holes for rods: a black ball has 4 holes, a white ball has 1, a red ball has 2 and a gray ball has 4. In a finished model, every hole holds a rod. Two rods between the same two balls make a double bond.

3Skaters rub wax on ledges and rails so their boards slide. Ledge wax is paraffin, which is made of separate molecules. Each molecule is a straight chain of carbon atoms. Each carbon is joined to the one or two carbons next to it in the chain, and all of its other holes hold hydrogen atoms. A common paraffin molecule has 25 carbon atoms in its chain.

4Some materials have too many atoms to build with a kit, so Ms. de Vries opened the viewer app. Table 1 shows what it displayed for five materials at the park. She pointed out that the formula of a molecule, such as CO₂, counts the atoms in one molecule. An extended structure has no separate molecules, so its formula shows the ratio of the kinds of atoms in its repeating pattern.

Use paragraphs 2 and 3. Mateus builds one paraffin molecule with 25 carbon atoms.

His model needs white balls, and it has balls in all.

Keziah looks for a rule that works for any straight paraffin chain. Which formula fits a chain with 18 carbon atoms?

A. C₁₈H₅₄
B. C₁₈H₃₈
C. C₁₈H₃₆
D. C₁₈H₇₂

Mateus tries to build a water molecule (H₂O) for the club's water bottles as a row: white, white, red. Using the kit rules, why can't this model be right?

A. The two white balls need a double bond, and the kit does not allow one.
B. A row of three balls has too many atoms to be a water molecule.
C. The red ball has 4 holes, so it would need four white balls around it.
D. The middle white ball has 1 hole, so it cannot join both of its neighbors.

The bubbles in sparkling water are carbon dioxide, CO₂. In the model, the black ball sits between the two red balls. Use paragraph 2.

A finished CO₂ model uses rods.

Extended structures in the viewer app

Use Table 1 and paragraph 4.

Table 1. What the Viewer App Shows
Material	Kinds of atoms	How atoms are joined	Separate groups?
Concrete sand (quartz)	Si, O	Each Si to 4 O; each O to 2 Si	None
Grip-tape grit	Si, C	Each Si to 4 C; each C to 4 Si	None
Steel rail	Mostly Fe (iron)	Each Fe packed against 8 Fe	None
Ice in the cooler	H, O	Each O to 2 H	Yes: H₂O groups
Ledge wax	C, H	Chains of 25 C with H	Yes: chains

In the materials with no separate groups, the pattern repeats in every direction out to the edges of the sample. In the ice, the H₂O groups are lined up in a repeating pattern, but they are only held near each other, not joined by bonds like the ones inside each group.

Which formula describes the quartz in the concrete sand?

A. SiO₂
B. Si₂O
C. Si₄O₂
D. SiO₄

Grip-tape grit is silicon carbide. Which formula describes it?

A. Si₄C
B. Si₂C
C. SiC
D. SiC₄

Keziah zooms in on a tiny chunk of the quartz pattern that holds 3,000 atoms in all.

The chunk has silicon atoms and oxygen atoms.

Match each tiny piece from the skate park to what the models say it contains.

A grain of concrete sand
A flake of ledge wax
A chip of ice
A shaving from the steel rail

A. Iron atoms packed in a pattern, with no molecules
B. Separate water molecules lined up in a pattern
C. Many separate chains of carbon and hydrogen
D. Silicon and oxygen atoms joined in one network

On a hot afternoon, the wax on a sunny ledge turns soft and smeary, but the sand grains in the concrete under it stay hard. Which explanation fits the models best?

A. Wax chains are separate and can slide past each other, but sand atoms are all joined.
B. Each grain of sand is a single small molecule, so it heats up more slowly than wax.
C. The heat breaks each wax molecule apart into loose carbon and hydrogen atoms.
D. Wax atoms are much larger than the atoms in sand, so they soak up more heat.

10.

Keziah says, "Grip-tape grit is made of SiC molecules, each one with one silicon atom and one carbon atom, just like sparkling water has CO₂ molecules." Do you agree? Write a claim, use evidence from Table 1 and the passage, and explain your reasoning with the models.