HS-PS2-6: How Molecular Structure Makes Designed Materials Work
In plain English: HS-PS2-6 is the NGSS high school performance expectation that asks students to communicate why the molecular-level structure of a designed material explains how it works. Students trace a property, such as conducting, stretching or binding, back to the attractive and repulsive electric forces between particles in a given structure. It is usually taught in Chemistry or Physics.
Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
Clarification Statement: Emphasis is on the attractive and repulsive forces that determine the functioning of the material. Examples could include why electrically conductive materials are often made of metal, flexible but durable materials are made up of long chained molecules, and pharmaceuticals are designed to interact with specific receptors.
Assessment Boundary: Assessment is limited to provided molecular structures of specific designed materials.
Next Generation Science Standards · Disciplinary Core Idea: Motion and Stability: Forces and Interactions · Official standard
Students explain how designed materials work by tracing each property back to the electric forces between the particles in a given molecular structure. They read provided structures of metals, polymers, gels and drug molecules, name where the attractive and repulsive forces act, connect those forces to a property such as conducting, stretching without breaking or binding to a receptor, and communicate the chain of reasoning in writing, in labeled diagrams and in short talks for different audiences.
The NGSS Clarification Statement says: "Emphasis is on the attractive and repulsive forces that determine the functioning of the material. Examples could include why electrically conductive materials are often made of metal, flexible but durable materials are made up of long chained molecules, and pharmaceuticals are designed to interact with specific receptors." The Assessment Boundary says: "Assessment is limited to provided molecular structures of specific designed materials." Every task on this page therefore gives students the structure; they are not asked to predict an unknown structure. Numerical data are invented but realistic, and the constants used are stated: copper resistivity 1.68 × 10-8 Ω·m and aluminum 2.65 × 10-8 Ω·m at 20 °C, atomic masses C 12.01, H 1.008, N 14.01, O 16.00, F 19.00 and Na 22.99 g/mol, a typical hydrogen bond of about 20 kJ/mol and a C-C bond of about 347 kJ/mol.
Learning Objectives
By the end of this lesson, students will be able to:
Identify, in a provided structure, where attractive and repulsive electric forces act: between ions and electrons, along covalent chains, and between chains or molecules
Explain why metals conduct electricity using the provided model of positive ions in a sea of shared electrons
Explain why long-chain and crosslinked polymers are flexible but durable, using the attractions summed along the chains and the covalent crosslinks
Explain why a drug molecule is designed to match a specific receptor, using the fit of charged, polar and nonpolar groups
Communicate a structure-force-property-function explanation to a stated audience, supported by data
Prior Knowledge Required
Students should already be comfortable with:
Atoms, molecules and extended structures MS-PS1-1
Using the periodic table to predict the outer electrons of an atom HS-PS1-1
Like charges repel and opposite charges attract, and the force grows as the charges get closer
Reading a simple structural formula with lines for covalent bonds
Hold up a phone charging cable with the end cut open, so students can see the copper strands and the plastic jacket.
Warm-Up Prompt
"This cable uses two very different materials. Why is the inside metal and the outside plastic? What would go wrong if the designers swapped them? Write your answer in two sentences for someone who has never taken chemistry."
Take three answers. Most will say that metal conducts and plastic does not. Ask the follow-up that drives the lesson: "What is different about the particles inside each material that makes this true?" Record student ideas without correcting them yet.
Direct Instruction15-20 minutes
Structure, force, property, function. Every property of a material comes from electric forces between its particles: opposite charges and partial charges attract, like charges and crowded electron clouds repel. Model an explanation in four links: the structure (what the particles are and how they are arranged), the force (which attraction or repulsion matters), the property that results, and the function it serves in the product. The same mobile electrons that carry charge through a metal also carry thermal energy through it quickly; in a material whose electrons are all held in bonds, energy spreads only as neighboring particles jostle one another, which is much slower. Repulsion matters as much as attraction: groups with the same charge push apart wherever a structure forces them close. Use Diagram 1 with Example 1 and Diagram 2 with Example 3.
Why wires are metal: copper core, PVC jacket
Provided structures: copper is a lattice of Cu+ ions whose outer electrons are shared by the whole lattice. PVC is made of chains -(CH2-CHCl)n- in which every electron sits in a covalent bond. Compare a 2.0 m wire of each with a 1.0 mm² cross-section.
Result: Copper: R = ρL/A = (1.68 × 10-8 Ω·m)(2.0 m) ÷ (1.0 × 10-6 m²) = 0.0336 Ω. PVC (ρ about 1013 Ω·m): R = 2 × 1019 Ω, about 6 × 1020 times larger. The shared electrons in copper feel attraction to all the ions, not one, so a small voltage moves them along the wire; PVC's bound electrons cannot move, so the jacket insulates.
Long chains: why polyethylene is tough and wax crumbles
Provided structures: candle wax is made of short molecules such as C25H52. A polyethylene milk jug is made of chains -(CH2-CH2)n- with about 20,000 repeat units. Both have only C-C and C-H bonds, and neighboring molecules attract through weak dispersion forces.
Result: Repeat unit C2H4 = 28.05 g/mol, so one chain is about 20,000 × 28.05 ≈ 561,000 g/mol, about 1,600 times the mass of a wax molecule (352.7 g/mol). Each chain touches many neighbors along its length and tangles with them, so the weak attractions add up: the jug bends without breaking, while wax molecules slide apart and crumble.
Hydrogen bonds between aligned chains: aramid (Kevlar) fiber
Provided structure: aramid chains are rigid, with flat benzene rings joined by amide groups -CO-NH-. The chains line up side by side, and each repeat unit forms 2 hydrogen bonds (N-H to O=C) with the next chain. Estimate for a segment of 500 repeat units, using about 20 kJ/mol per hydrogen bond.
Result: 500 × 2 = 1,000 hydrogen bonds × 20 kJ/mol ≈ 20,000 kJ/mol, about 58 times the energy of one C-C bond (347 kJ/mol). Sliding one chain past its neighbor would mean breaking all of them at once, so the load is shared along the chains: the fiber is very strong for its mass and is used in cut-resistant gloves and protective vests.
Attraction and repulsion in a gel: superabsorbent polymer
Provided structure: sodium polyacrylate chains carry many -COO- groups with Na+ ions nearby, and a few covalent crosslinks join the chains into a network. Invented test: 0.50 g absorbs 150 g of deionized water but only 25 g of 0.9% salt water.
Result: 150 ÷ 0.50 = 300 g of water per gram; 25 ÷ 0.50 = 50 g per gram, 6 times less. Polar water molecules are attracted to the ions, and the -COO- groups repel each other, spreading the network open. Dissolved salt ions crowd around the charged groups and weaken both effects, so the gel swells less.
Designed to fit: a drug and its receptor
Provided structures (simplified): a receptor pocket has a negatively charged -COO- group, a C=O group that can accept a hydrogen bond and a nonpolar pocket. Drug candidate A has an -NH3+ group, an -OH group and a nonpolar ring spaced to match; candidate B is the same but has a -CH3 where A has the -NH3+.
Result: A forms an ionic attraction, a hydrogen bond and a nonpolar contact; B loses the ionic attraction. By Coulomb's law the force between the charged groups grows as 1/r², so moving from 0.60 nm to 0.30 nm apart multiplies it by 4: a close, exact fit matters. A binds more strongly, which is why drug designers match groups to one specific receptor.
After each example, have students say the four links aloud: "The structure has ___, so ___ attracts or repels ___, which makes the material ___, so it can ___." Point out that a single idea, electric force between particles, explains all five materials.
Guided Practice15 minutes
Pairs get four structure cards and invented, realistic data for a drop of water on each surface. The contact angle is the angle between the surface and the edge of the drop: above 90° the drop beads up, below 90° it spreads.
Guided practice data: water contact angles (invented, realistic values)
Surface
Provided structure
Contact angle
PTFE tape
-(CF2-CF2)n-: chain covered by fluorine atoms
112°
Polyethylene film
-(CH2-CH2)n-: nonpolar chain
96°
Nylon-6,6 fabric
Chains with -CO-NH- groups every few atoms
70°
Clean glass
Si-O network with -OH groups at the surface
25°
Rank the surfaces from most to least water-repellent and mark which two make water bead up.
For each surface, find the groups on the provided structure that water could attract: N-H, C=O and O-H groups can form hydrogen bonds with water; the fluorine-covered and C-H surfaces cannot.
Explain the ranking with forces: for each surface, decide which attraction is stronger, water to water or water to surface, and connect that to the shape of the drop.
Write a 40-word explanation for the back of a PTFE tape package that names the structure, the force and the property.
Independent Practice10-15 minutes
Each student writes a one-paragraph technical note and draws a labeled sketch about rubber for a bicycle tire company. Provided structure: natural rubber is polyisoprene, -(C5H8)n-, with about 5,000 repeat units per chain. Heating it with sulfur (vulcanizing) adds covalent S-S crosslinks between chains about every 100 repeat units.
Independent practice data: strips stretched to 3.0 times their length, then released (invented)
Sample
Length after release
Rubber without crosslinks
1.8 times the original
Vulcanized rubber
1.05 times the original
Students compute the permanent stretch (80% against 5%) and the mass of one chain (C5H8 = 68.11 g/mol, so about 340,600 g/mol). The note must explain, with forces, why coiled chains can straighten when pulled, why chains without crosslinks slide past each other and stay stretched, and why the crosslinks pull the network back. It ends with one sentence on why tires are vulcanized.
Closure5 minutes
Exit ticket: give students the provided structures of aluminum foil (Al3+ ions sharing their outer electrons) and plastic food wrap (polyethylene chains). "In two sentences for a grade 6 student, explain which one would light an LED tester and why, naming the particles that move." Collect and sort the answers into complete four-link explanations and partial ones to plan the next lesson.
Differentiation Strategies
For Struggling Students
Give a four-box organizer (structure, force, property, function) and fill in the first box for each material
Color-code the structure cards: blue for full or partial positive charges, red for negative, gray for nonpolar regions
Provide word banks for each material, such as shared electrons, hydrogen bond, crosslink, repel, attract
For Advanced Students
Compare the density-adjusted strength of aramid fiber and steel wire from published data, and write a design memo for a lightweight rope
Research one real drug and its receptor from a public database, and draw the provided structures with each attraction labeled
Explain why graphite conducts along its layers but not between them, using its provided layered structure
Assessment Guidance
What to Look For
Check that explanations name particles and forces, not only properties: "copper conducts because it is a metal" restates the claim, while "the shared outer electrons can move through the lattice of positive ions" explains it. Listen for students who say that atoms or ions flow in a wire, that polymer chains are held to each other by covalent bonds everywhere, or that a drug is shaped like a key with no mention of attractions. Check that each written piece fits its audience: accurate words for a technical note, plain words with no loss of accuracy for a customer.
02
Classroom Activities
3 Activities
1
Material Property Stations: Collecting Evidence for Structure
25 minGroups of 3-4
Groups rotate through four stations, test a property of everyday designed materials and match each result to a provided structure card. Each group then makes one poster that explains two of the materials with the four links: structure, force, property, function.
Procedure
Station 1, conductivity: touch the LED tester clips to copper wire, aluminum foil, a plastic straw, a rubber band and PTFE tape. Record which light the LED.
Station 2, stretch: stretch a rubber band and a strip cut from a thin plastic bag to about three times their length, release, and compare the lengths after release.
Station 3, absorb: weigh 1.0 g of superabsorbent crystals into each of two cups, add tap water to one and salt water (1 teaspoon of salt per cup of water) to the other a little at a time, and record the mass of liquid each can hold.
Station 4, water drops: put one drop of water on PTFE tape, plastic wrap and printer paper, and sketch each drop from the side.
Safety: wear goggles at Station 3, do not inhale or taste the crystals, wipe up spilled gel at once because it is slippery, wash hands afterward, and put used gel in the trash, never down the sink, where it can swell and block the drain. Use only the battery testers, never a wall outlet.
Sample Data (invented)
Station 1: the LED lit for copper wire and aluminum foil only. Station 3: 1.0 g of crystals held 200 g of tap water and 35 g of salt water. Station 2: the rubber band returned almost to its original length; the plastic strip stayed longer and thinner.
Discussion Questions
Only the two metals lit the LED. What do their provided structures have that the other three lack?
The crystals held about 5.7 times more tap water than salt water. Use the words attract and repel to explain the difference.
Which station gave the weakest evidence for its structure card, and what extra test would make it stronger?
Modification for Distance Learning
Show short teacher videos of each station with the sample data on screen. Students complete the evidence table at home and build the poster as a shared slide.
2
Design Brief Pitch: Choose the Structure for the Job
20 minGroups of 3
Each group draws one design brief and a set of six provided structure cards: copper, PVC, PTFE, sodium polyacrylate, vulcanized polyisoprene and nylon-6,6. They choose the material or pair of materials for the brief and give a two-minute pitch to a mock client, with a labeled structure sketch.
Design Briefs
A headphone cable that carries a signal and is safe to hold.
A frying pan surface that eggs do not stick to.
The absorbent core of a disposable diaper.
A bicycle tire that stretches over bumps and springs back.
Toothbrush bristles that bend without snapping and dry quickly.
Pitch Requirements
Name the chosen structure and point to the feature that matters on the sketch.
Name the force: which particles attract or repel, and where.
Link the force to the property and the property to the brief.
Answer one question from the client group, which uses a checklist to score each of the four links.
Discussion Questions
Which briefs needed two materials, and why could one structure not do both jobs?
Which pitch explained a force most clearly, and what made it clear?
How would your pitch change if the client were an engineer instead of a store buyer?
Modification for Distance Learning
Groups record a two-minute video pitch with a sketch on screen and post it; each student scores two other pitches with the checklist.
3
Fix the Ad: Correcting Claims About Materials
20 minPairs
Pairs read four invented advertisements that each misuse a molecular idea. With the provided structure beside each ad, they find the error and rewrite the ad in 40 words or fewer so that it is accurate and still appealing to a customer.
Ad Cards (invented)
Ad 1, frying pan: "Our PTFE coating is so sticky to itself that nothing else can get a grip."
Ad 2, extension cord: "Pure copper atoms race through the wire to carry power to your tools."
Ad 3, pain reliever: "Works on every receptor in your body, so it helps everywhere."
Ad 4, cut-resistant gloves: "Every aramid fiber is welded to its neighbors by covalent bonds, making one giant molecule."
Checklist for Each Rewrite
The rewrite names the real feature of the provided structure.
It names the attraction or repulsion that matters, and between which particles.
It connects that force to the product's job.
It uses words a customer understands and makes no claim the structure cannot support.
Discussion Questions
Which ad's error could lead a customer to a wrong or unsafe decision?
How did you keep the rewrite short without losing accuracy?
Swap rewrites with another pair. Which of their sentences would you change, and why?
Challenge Variation
Pairs write a fifth ad of their own for a material from Activity 1 or 2 with one hidden error, then trade it with another pair to fix.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Where the Electrons Are in a Metal Wire and in Its Plastic Jacket
Simplified models, not to scale. Left: in copper, positive ions sit in a regular lattice and their outer electrons (blue dots) are shared by the whole lattice, so a voltage makes them drift along the wire. Right: in PVC, -(CH2-CHCl)n-, every electron is held in a covalent bond along the chain, so the jacket does not conduct.
Diagram 2: Hydrogen Bonds Between Aligned Aramid Chains
Simplified model of two aramid (Kevlar) chains, not to scale, with three repeat units each. Each link between rings is really an amide group, -CO-NH-, whose C=O and N-H point to opposite sides; for clarity only the half that faces the other chain is drawn (the C with its O, or the N with its H). Each repeat unit has one C=O and one N-H group facing the other chain, giving 2 hydrogen bonds per repeat unit (6 dashed lines). The partial negative O on one chain attracts the partial positive H on the other, so the rigid chains stay lined up and share a pulling load.
04
Homework Assignment
~30 min
HS-PS2-6 Homework: Explaining Designed Materials from Their Structures
Directions: Each problem gives the molecular structure you need; do not look up others. Data are invented but realistic. Show calculations with units, and in every explanation name the structure, the force (which particles attract or repel) and the property it causes.
Part 1: Structure and Properties from Data (Problems 1-2)
Two kinds of polyethylene have the same repeat unit, -(CH2-CH2)n-. In low-density polyethylene (LDPE) the chains have many short branches; in high-density polyethylene (HDPE) they are almost unbranched. Data: density 0.92 and 0.96 g/cm³; tensile strength 10 and 30 MPa. (a) How many times stronger is HDPE, and by what percent is it denser? (b) Explain both differences using how closely the chains can pack and the attractions between them. (c) Write one sentence for a dairy explaining why HDPE suits a milk jug that must not split when dropped.
Aluminum is a lattice of Al3+ ions with shared outer electrons, like copper. A power company compares 10 m wires with a 2.0 mm² cross-section: ρ = 2.65 × 10-8 Ω·m for aluminum and 1.68 × 10-8 Ω·m for copper. (a) Find the resistance of each wire. (b) What cross-section would the aluminum wire need to match the copper wire's resistance? (c) Explain, using the provided structure, why both metals conduct and why the wire's coating is a polymer.
Part 2: Communicating Structure and Function (Problems 3-4)
Farmers mix hydrogel beads into dry soil. Provided structure: crosslinked chains with many -COO- K+ groups. In a test, 1.0 g of beads holds 180 g of rainwater but only 45 g of water containing dissolved fertilizer salts. (a) Find the percent decrease in water held. (b) Write a 100-word explanation for a farmers' newsletter that uses the words attract and repel. (c) Explain what would happen to the beads without crosslinks.
Provided structures (simplified): a receptor pocket has an -NH3+ group, an O-H group and a nonpolar pocket. Candidate X has a -COO- group, a C=O group and a nonpolar ring spaced to match. Candidate Y has an -NH3+ group where X has its -COO-. Candidate Z matches X but has an -OH where X has its ring. (a) Rank the candidates from strongest to weakest binding. (b) Explain each place in the ranking with attractions and repulsions. (c) Write two sentences for a patient leaflet on why the drug acts on this receptor and not on others.
Part 3: Design Choices (Problems 5-6)
Provided structures: nylon-6,6 has flexible chains joined to neighbors by hydrogen bonds; ultra-high-molecular-weight polyethylene (UHMWPE) has extremely long, aligned -(CH2-CH2)n- chains held only by dispersion attractions; aramid has rigid aligned chains with hydrogen bonds. Fiber data: strength 0.9, 3.4 and 3.6 GPa; density 1.14, 0.97 and 1.44 g/cm³; nylon melts at 264 °C, UHMWPE at 147 °C, and aramid breaks down near 500 °C without melting. (a) Find each fiber's strength divided by density. (b) Choose a fiber for a sailing line that must float and one for a firefighter's rescue rope. (c) Write a short memo that justifies each choice from the structures.
A soft contact lens is made of a lightly crosslinked polymer whose chains carry many -OH groups. A dry lens has a mass of 31 mg and the same lens fully hydrated has a mass of 50 mg. (a) Find the water content as a percent of the hydrated mass. (b) Explain, with the force involved, why the -OH groups hold water. (c) Explain why the lens keeps its shape instead of dissolving, and write one sentence an eye doctor could say to a patient about it.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Uses the Provided Structure
Points to the specific feature (shared electrons, chain length, crosslinks, charged or polar groups) that matters
Names the material type but not the feature
Forces
Names which particles attract or repel and connects that force to the property
Mentions a force without saying where it acts or what it causes
Data and Calculations
Correct values with units, used as evidence in the explanation
Correct method with one error, or values not used as evidence
Communication
Accurate, complete and suited to the stated audience
Accurate but missing a link, or not suited to the audience
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Every question gives the structure you need. Data are invented but realistic. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Provided structure: a metal is a lattice of positive ions whose outer electrons are shared by the whole lattice. Why does this structure make metals good electrical conductors?
Answer: A
Each shared electron is attracted to many ions at once rather than bound to one, so a small push from a voltage moves it along. Choice B is a common misconception: the ions stay in place. Choice D describes a covalent network, not the provided metal structure.
Question 2 of 20 · Multiple Choice
Two samples have the same repeat unit, -(CH2-CH2)n-. Sample 1 has chains of about 30 repeat units; sample 2 has chains of about 30,000. Which is tougher, and why?
Answer: C
Dispersion attractions are weak one by one, but a chain 1,000 times longer has about 1,000 times more contacts with its neighbors, and long chains knot around each other. Pulling them apart takes much more force. Choice B ignores chain length. Choice D is wrong for this structure: nothing but weak attractions joins the chains.
Question 3 of 20 · Multiple Choice
Provided structure: PTFE is -(CF2-CF2)n- (repeat unit C2F4, 100.02 g/mol). About what is the molar mass of a chain of 5,000 repeat units?
Answer: B
5,000 × 100.02 g/mol = 500,100 g/mol ≈ 5.0 × 105 g/mol. Choice A is off by a factor of 100. Choice D uses CF2 (about 50 g/mol) as the repeat unit instead of C2F4.
Question 4 of 20 · Multiple Choice
Provided structure: nylon-6,6 chains contain -CO-NH- groups every few atoms, and neighboring chains line up with these groups facing each other. Which force mainly holds neighboring chains together?
Answer: D
The partially positive H on N is attracted to the partially negative O of a C=O group on the next chain. Choice A confuses the bonds along a chain with the attractions between chains. Choice B names ions that are not in the structure.
Question 5 of 20 · Multiple Choice
Provided structures: gels H and L are made of the same chains with -COO- Na+ groups, but gel H has many more covalent crosslinks between chains than gel L. Which prediction is best supported?
Answer: A
The charged groups pull water in and push each other apart in both gels, but the crosslinks are covalent ties that stop the chains from moving far apart. More ties mean a tighter network that opens less. Choice B treats crosslinks as the water-attracting part, when the -COO- groups do that. Choice C ignores the crosslinks.
Question 6 of 20 · Multiple Choice
Provided structures: a cured epoxy glue is one network of chains joined by many covalent crosslinks; a hot-melt glue is made of long chains with no crosslinks. Which glue softens and flows again when reheated, and why?
Answer: B
Heat makes chains move more; chains held only by attractions between chains can then slide past each other and flow. The covalent crosslinks in epoxy tie every chain into one network, so it does not flow. Choice A reverses the roles, and choice D forgets that the bonds between hot-melt chains are not covalent.
Question 7 of 20 · Multiple Choice
A receptor pocket is lined with nonpolar -CH3 groups and has no charged or polar groups. A chemist can put one of four groups on a drug at the spot that sits in this pocket. Which choice fits best?
Answer: C
A nonpolar ring is attracted to the nonpolar pocket by dispersion forces. Charged or polar groups (choices A, B and D) are strongly attracted to water outside the pocket and would give up those attractions for nothing, because the pocket has no charges or partial charges to attract them.
Question 8 of 20 · Multiple Choice
A copper wire (ρ = 1.68 × 10-8 Ω·m) is 5.0 m long with a cross-section of 0.50 mm². What is its resistance?
Answer: D
0.50 mm² = 0.50 × 10-6 m², so R = (1.68 × 10-8)(5.0) ÷ (0.50 × 10-6) = 0.168 Ω. Choice A is 10 times too small, from dividing by 5.0 × 10-6 m² instead. Choice B is the resistivity, not a resistance, and choice C uses 0.50 as if the area were in m², skipping the conversion from mm².
Question 9 of 20 · Multiple Choice
A rain jacket has a coating whose provided structure is a polymer backbone with -CF2-CF3 side chains sticking out at the surface. Why does rain bead up and roll off?
Answer: B
Water spreads on surfaces that offer O-H, N-H or charged groups to attract it. A fluorine-covered surface offers none, so the stronger attraction is between water molecules, and the drop stays round. Choice A is wrong: the coating is not charged. Choice C describes a hydrogel, the opposite design.
Question 10 of 20 · Multiple Choice
Which sentence best communicates to a customer why aramid gloves resist cuts? (Provided: rigid chains lined up side by side, with hydrogen bonds between neighboring chains.)
Answer: A
It names the structure (aligned rigid chains), the force (attraction between neighbors) and links them to the property, in plain words. Choice B restates the claim without explaining it. Choice D is false and unrelated to the provided structure.
Question 11 of 20 · Multiple Choice
In a model of a drug binding site, a charged group on the drug moves from 0.8 nm to 0.4 nm from an oppositely charged group on the receptor. By Coulomb's law, how does the attractive force change?
Answer: C
Force varies as 1/r². Halving r multiplies the force by 2² = 4. Choice A treats the force as 1/r. Choice D inverts the relationship, as if the force grew with distance.
Question 12 of 20 · Multiple Choice
A material conducts electricity, can be hammered into thin sheets without shattering, and reflects light. Which provided structure fits these observations?
Answer: D
Free-moving shared electrons carry current and reflect light, and the provided metal model is the only one with them. Choice C is an ionic solid: with no free electrons, it does not conduct as a solid. Choices A and B are molecular and polymer structures whose electrons are all held in bonds.
Question 13 of 20 · Multiple Choice
Pan makers shape metal sheets with hammers and presses, but they could not shape an ionic crystal that way. Provided structures: in a metal, positive ions sit in layers in a sea of shared electrons; in an ionic crystal such as table salt, positive and negative ions alternate in every direction. Both are hit with a hammer. Which one shatters, and why?
Answer: A
When a layer of the salt crystal shifts by one ion, positive ions line up next to positive ions and negative next to negative, and the repulsion splits the crystal. In the metal, the shared electrons still attract the ions after the layers slide, so it bends instead. Choice C is true of both but does not explain the difference, and choice D contradicts the provided structure.
Question 14 of 20 · Multiple Choice
A hydrogel wound dressing has a dry mass of 12 mg and a mass of 30 mg when fully swollen. What percent of the swollen dressing is water?
Answer: B
Water = 30 - 12 = 18 mg, and 18 ÷ 30 = 60%. Choice A is the polymer share. Choice C divides by the dry mass (18 ÷ 12), and choice D compares the swollen mass with the dry mass.
Question 15 of 20 · Short Answer
Provided structures: two nylon fibers have the same chains, with -CO-NH- groups every few atoms. In fiber 1 the chains are randomly coiled; fiber 2 was stretched during manufacture so its chains lie parallel along the fiber. Which fiber is stronger along its length? Explain with forces.
Fiber 2. When the chains lie parallel, many more N-H and C=O groups on neighboring chains line up and form hydrogen bonds, so each chain is held by its neighbors along its whole length and a pull is shared by many chains. In the coiled fiber, fewer groups line up, and a pull first straightens chains instead of loading them, so it stretches and breaks more easily.
Question 16 of 20 · Short Answer
Provided structure: in an aramid fiber, each repeat unit forms 2 hydrogen bonds with the neighboring chain. Using about 20 kJ/mol per hydrogen bond and 347 kJ/mol for a C-C bond, estimate the total hydrogen-bond energy along a segment of 300 repeat units and explain what the comparison means for the fiber.
300 × 2 = 600 hydrogen bonds, and 600 × 20 = 12,000 kJ/mol, about 35 times one C-C bond. Sliding the chain past its neighbor would mean breaking all these attractions together, so the chains stay locked side by side and the load spreads along them, which makes the fiber very strong.
Question 17 of 20 · Short Answer
A tire company compares a new polymer fiber (strength 2.8 GPa, density 1.40 g/cm³) with steel wire (strength 1.6 GPa, density 7.85 g/cm³) for the belts inside a bicycle tire. Compute strength divided by density for each and write one sentence of advice for the company.
Fiber: 2.8 ÷ 1.40 = 2.0 GPa per g/cm³. Steel: 1.6 ÷ 7.85 ≈ 0.20 GPa per g/cm³. For the same mass the fiber is about 10 times stronger, so it can make a lighter tire of the same strength.
Question 18 of 20 · Short Answer
A classmate wrote: "Plastic food wrap does not conduct electricity because it has no electrons." The provided structure of the wrap is polyethylene, -(CH2-CH2)n-. Rewrite the sentence so it is accurate for a grade 8 audience, and say what was wrong.
A strong answer: "Plastic wrap has plenty of electrons, but each one is held in a bond between two particular atoms, carbon to carbon or carbon to hydrogen. None of them is free to travel through the plastic, so a battery cannot push a current through it." The error was saying the plastic has no electrons; the point is that its electrons cannot move.
Question 19 of 20 · Short Answer
A company tests 2.0 g of a superabsorbent polymer (provided structure: crosslinked chains with -COO- Na+ groups). It absorbs 560 g of deionized water and 84 g of salt water. Find the grams absorbed per gram in each case, the percent decrease, and explain the decrease.
Deionized: 560 ÷ 2.0 = 280 g/g. Salt water: 84 ÷ 2.0 = 42 g/g. Decrease: (280 - 42) ÷ 280 = 85%. The dissolved ions shield the -COO- charges, so the groups repel each other less and pull less water in, and the network opens less.
Question 20 of 20 · Short Answer
Provided structures: an aluminum pot is a lattice of Al3+ ions with shared outer electrons; its handle is a thermoset plastic, a network of covalent chains with every electron in a bond. Explain to a customer why the pot heats food quickly but the handle stays cool enough to hold.
A strong answer: the shared electrons in aluminum move freely, so they carry energy from the hot burner through the metal quickly (the same free electrons that let metals conduct electricity). In the plastic handle every electron is held in a bond, so energy passes only slowly from one vibrating chain to the next, and the handle warms up much more slowly.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-PS2-6 mean?
HS-PS2-6 asks students to communicate why the molecular-level structure of a designed material explains how it works. Students trace a property back to attractive and repulsive electric forces between particles and explain it clearly in writing, diagrams or talks. The code means High School, Physical Science, core idea 2 (Motion and Stability: Forces and Interactions), performance expectation 6.
Is HS-PS2-6 taught in chemistry or physics?
It is usually taught in Chemistry, in units on bonding and intermolecular forces, and it also fits Physics units on electric forces. Because it sits in the forces core idea, it pairs well with Coulomb's law (HS-PS2-4).
What is the assessment boundary for HS-PS2-6?
The official Assessment Boundary limits assessment to provided molecular structures of specific designed materials. Students are always given the structure; they are not expected to work out an unknown structure from scratch. Every task on this page follows that rule.
What materials are good examples for HS-PS2-6?
The Clarification Statement names three: metals for electrical conductors, long-chain molecules for flexible but durable materials, and drugs designed for specific receptors. Other good examples with clear structures are nonstick PTFE, superabsorbent gels, vulcanized rubber, contact lens hydrogels and aramid fibers.
What forces do students need to talk about?
Electric forces between particles: attraction between opposite charges or partial charges (including ionic attractions and hydrogen bonds), weak dispersion attractions between nonpolar chains, and repulsion between like charges. Students should say which particles attract or repel and where, not only name the force.
What does communicate mean in an NGSS standard?
It means students explain scientific and technical information clearly to an audience, in forms such as written explanations, labeled diagrams, data tables, posters, memos and short talks. Good communication for HS-PS2-6 links structure, force, property and function, and fits the audience without losing accuracy.
What are common misconceptions about why metals conduct?
A common one is that metal atoms or ions flow through the wire. In the provided model the ions stay in place and the shared outer electrons move. Another is that metals conduct because they are hard or shiny; those are separate results of the same shared-electron structure.
Do students need to draw molecular structures from memory?
No. For HS-PS2-6 the structures are provided. Students need to read them: spot the charged or polar groups, the chain length, branches and crosslinks, and use those features in an explanation.
How can I assess HS-PS2-6 in class?
Give a provided structure and a real product, then ask for a short explanation for a named audience. Score the four links (structure, force, property, function) plus accuracy and fit to the audience, as in the rubric on this page. Critiquing a flawed claim, as in the Fix the Ad activity, also works well.
How does HS-PS2-6 connect to other NGSS standards?
It builds on MS-PS1-1 (models of molecules and extended structures) and MS-PS1-3 (synthetic materials from natural resources). It sits alongside HS-PS1-3, which infers the strength of electric forces between particles from bulk properties, and HS-PS2-4, which uses Coulomb's law. It leads into engineering design standards such as HS-ETS1-3, where material choices are weighed against criteria.
07
Related Standards
5 standards
These standards connect to HS-PS2-6: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-PS1-1Prerequisite
Develop models of the atomic composition of simple molecules and extended structures
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
