MS-PS1-1: Modeling Simple Molecules and Extended Structures
In plain English: MS-PS1-1 is the NGSS middle school performance expectation that asks students to build and use models that show which atoms, and how many of each, make up simple molecules such as ammonia and methanol and extended structures such as salt and diamond. It is usually taught in grade 6, 7 or 8 physical science.
Develop models to describe the atomic composition of simple molecules and extended structures.
Clarification Statement: Emphasis is on developing models of molecules that vary in complexity. Examples of simple molecules could include ammonia and methanol. Examples of extended structures could include sodium chloride or diamonds. Examples of molecular-level models could include drawings, 3D ball and stick structures or computer representations showing different molecules with different types of atoms.
Assessment Boundary: Assessment does not include valence electrons and bonding energy, discussing the ionic nature of subunits of complex structures, or a complete description of all individual atoms in a complex molecule or extended structure is not required.
Next Generation Science Standards · Disciplinary Core Idea: Matter and Its Interactions · Official standard
Students build and draw models that show what simple molecules and extended structures are made of. An atom is the smallest particle of an element, and an element is a substance made of only one kind of atom, such as carbon or oxygen. A molecule is a small group of atoms joined together that moves around as one unit, and every molecule of a substance has the same atoms. An extended structure is a huge, repeating pattern of joined atoms with no set size, like the grains of table salt or a diamond. Students count the atoms of each element in molecules, describe the repeating ratio in extended structures, and compare drawings, ball-and-stick models and computer models.
The NGSS Clarification Statement says: "Emphasis is on developing models of molecules that vary in complexity. Examples of simple molecules could include ammonia and methanol. Examples of extended structures could include sodium chloride or diamonds. Examples of molecular-level models could include drawings, 3D ball and stick structures or computer representations showing different molecules with different types of atoms." The Assessment Boundary says: "Assessment does not include valence electrons and bonding energy, discussing the ionic nature of subunits of complex structures, or a complete description of all individual atoms in a complex molecule or extended structure is not required." So this page does not discuss electrons, why atoms join, or the electric charge on the particles in salt. In models, a stick only shows that two atoms are joined. Students do the practice of developing models: they build, draw, count, compare and fix models.
Learning Objectives
By the end of this lesson, students will be able to:
Use a chemical formula to tell which elements are in a molecule and how many atoms of each it has
Build and draw ball-and-stick models of simple molecules such as ammonia and methanol, with a key for each kind of atom
Describe an extended structure, such as sodium chloride or diamond, as a repeating pattern of atoms with a fixed ratio but no set size
Sort substances into simple molecules and extended structures using evidence from a model
Compare drawings, 3D ball-and-stick models and computer models, and find and fix errors in a model
Prior Knowledge Required
Students should already be comfortable with:
Matter is made of particles too small to be seen 5-PS1-1
Ratios as a comparison of two amounts, such as 1 to 2 6.RP.A.1
Pass around a magnifier and a few grains of table salt on a dark card. Students notice that the grains have flat faces and square corners. Then ask:
Warm-Up Prompt
"A grain of salt looks like a tiny cube. If you could zoom in until you saw the particles it is made of, what do you think you would see? Draw a quick sketch. Would a bigger grain be made of different particles, or more of the same ones?"
Collect a few sketches. Many students draw dots or tiny cubes. Keep them on the board: at the end of the lesson students compare them with Diagram 2.
Direct Instruction15-20 minutes
Reading a chemical formula. A chemical formula uses letters for elements and small numbers called subscripts for how many atoms of that element there are. No subscript means 1. In H₂O there are 2 hydrogen atoms and 1 oxygen atom. A model is a drawing or object that stands for something too small, too big or too hard to see. In a ball-and-stick model, each ball is one atom, the color or letter tells the element, and each stick shows two atoms that are joined. Every model needs a key that says which color is which element. Show Diagram 1, then work the examples.
Simple molecule: ammonia (official example)
Ammonia, NH₃, is a gas found in some glass cleaners. Build and describe one molecule.
Result: N has no subscript, so 1 nitrogen atom; H₃ means 3 hydrogen atoms. Total 1 + 3 = 4 atoms of 2 elements. Model: one nitrogen ball in the middle with three hydrogen balls joined to it, all on one side, like a short tripod (Diagram 1).
Simple molecule: methanol (official example)
Methanol, CH₃OH, is a fuel used in some racing cars. Its formula is written to show that one hydrogen is joined to the oxygen.
Result: Count every letter: C = 1, H = 3 + 1 = 4, O = 1. Total 6 atoms of 3 elements (the formula CH₄O has the same count). Model: carbon in the center joined to 3 hydrogen balls and 1 oxygen ball; the fourth hydrogen is joined to the oxygen.
Table salt is sodium chloride, NaCl. A group builds a small cube of it with 2 balls along each edge, alternating sodium and chlorine so that no two of the same kind touch.
Result: The cube has 2 × 2 × 2 = 8 balls: 4 sodium and 4 chlorine, a 1 : 1 ratio. A real grain repeats this pattern in every direction, far past any model, so NaCl tells the ratio (1 sodium for every 1 chlorine), not the size of a molecule.
Extended structure: diamond (official example)
A diamond is made only of carbon atoms. Each carbon is joined to 4 others, and those are joined to more, in a 3D network with no end inside the crystal.
Result: One element, so the formula is just C. There is no small group to count: a diamond in a ring is one connected piece. A model shows a few carbon balls, each with 4 sticks, and a note that the pattern keeps going.
Same ratio, different kind of structure
Carbon dioxide (CO₂) is the gas you breathe out. Quartz, the hard mineral in most sand, is silicon dioxide (SiO₂).
Result: CO₂ is a simple molecule: each one has exactly 3 atoms, 1 carbon and 2 oxygen. SiO₂ is an extended structure: a giant network with 2 oxygen atoms for every silicon atom. A quartz model with 9 silicon balls needs 9 × 2 = 18 oxygen balls.
After each example, ask: "Can you count all the atoms in one unit of this substance? If yes, it is a simple molecule. If the pattern just keeps repeating, it is an extended structure, and the formula gives the ratio." Then show Diagram 2 and point out the dashed lines: the real crystal keeps going.
Guided Practice15 minutes
Pairs fill in the table for four simple molecules, then build any two with clay balls and toothpicks. They make a key first. The teacher circulates and asks each pair to point to the subscript that tells them how many balls of each color to use.
Guided practice: reading formulas (students fill in the last three columns)
Substance
Formula
Elements
Atoms of each
Total atoms
Water
H₂O
hydrogen, oxygen
2 H, 1 O
3
Oxygen gas
O₂
oxygen
2 O
2
Carbon monoxide
CO
carbon, oxygen
1 C, 1 O
2
Butane (lighter fuel)
C₄H₁₀
carbon, hydrogen
4 C, 10 H
14
Read each letter as an element and each subscript as a number of atoms. Remember that no subscript means 1.
Add the atoms to get the total for one molecule.
Notice that oxygen gas has only one element but is still a molecule: two oxygen atoms joined together.
Build two of the molecules. Check: does your model have exactly the atoms the formula says, and does your key match your colors?
Independent Practice10-15 minutes
Each student gets four substance cards: chlorine gas (Cl₂, used to clean pool water), a gold ring (only gold atoms, Au), hydrogen sulfide (H₂S, the gas that smells like rotten eggs) and an iron nail (only iron atoms, Fe). For each card, the student decides whether it is a simple molecule or an extended structure and gives a reason. For the molecules, they count the atoms (2 and 3). Then they draw one ball-and-stick model of a molecule and one model of a small piece of an extended structure, each with a key and with dashed lines where the pattern continues.
Closure5 minutes
Exit ticket: "You can count all the atoms in one molecule of methanol. Why can't you count all the atoms in one 'unit' of table salt? What does the formula NaCl tell you instead?" Return to the warm-up sketches: a bigger salt grain has more of the same particles in the same repeating pattern, not different particles.
Differentiation Strategies
For Struggling Students
Give a formula-reading strip with each element in its own box and the subscript under it, so students count one element at a time
Pre-make a color key card (for example black = carbon, white = hydrogen, blue = nitrogen, red = oxygen) that students keep next to their models
Start with two-atom and three-atom molecules (O₂, CO, H₂O) before ammonia and methanol
For Advanced Students
Ask students to build two different models that both have 4 carbon and 10 hydrogen atoms, and explain why the formula alone does not show how atoms are arranged
Have students use a free online molecule viewer to rotate methanol and diamond and write one thing the computer model shows better than the clay model, and one thing it hides
Ask students to predict how many balls of each kind a 4 × 4 × 4 salt cube would need and explain why the numbers come out equal
Assessment Guidance
What to Look For
Check that students read subscripts as the number of atoms of the element just before them, and that "no subscript" means 1. Look for models with a key, the right number of balls of each color, and dashed lines or a note when a structure continues. Listen for students who call a piece of salt or diamond "a molecule" with a fixed number of atoms, or who think the colors in a model are the real colors of atoms.
02
Classroom Activities
3 Activities
1
Build-a-Molecule Stations
20 minPairs
Pairs visit four stations, each with a formula card and a picture of where the substance is found. At each one they build a ball-and-stick model from modeling clay and round toothpicks (or a model kit), sketch it with a key and record the atoms of each element.
Stations
Station 1: water, H₂O
Station 2: carbon dioxide, CO₂
Station 3: ammonia, NH₃
Station 4: methanol, CH₃OH
To build all four, a pair needs 9 hydrogen, 4 oxygen, 2 carbon and 1 nitrogen balls: 16 balls in all. Pairs reuse the clay between stations if supplies are short. Safety: use round toothpicks, keep the points away from faces, and do not eat any modeling materials.
Discussion Questions
Water and carbon dioxide both have 3 atoms. What is different about what they are made of?
Methanol has more atoms than ammonia. Which one has more kinds of atoms?
Your clay balls are much bigger than real atoms and are colors that real atoms do not have. Why is the model still useful?
Modification for Distance Learning
Students build the four molecules with any small household objects (buttons, coins, pasta pieces) and photograph each model next to a handwritten key.
2
Grow the Crystal: Extended Structure Builds
20 minGroups of 3-4
Groups use foam balls or large beads in two colors joined with pipe cleaner pieces to build pieces of a sodium chloride model, alternating the two colors so that no two balls of the same color are next to each other. Then they build a small piece of a diamond model.
Procedure
Build a cube with 2 balls along each edge. Count the balls of each color.
Grow it into a cube with 3 balls along each edge, starting from a large (chlorine) ball at each corner. Count again.
Diamond: build a piece where one carbon ball in the middle is joined to 4 others that point to the corners of a pyramid shape. Add one more carbon to each outer ball.
Sample Results
2-ball cube: 8 balls, 4 of each color. 3-ball cube: 27 balls, 14 chlorine and 13 sodium. Diamond piece: 1 middle carbon, 4 joined to it, then 4 more: 9 carbon balls, all the same color.
Discussion Questions
The 3-ball cube has one more chlorine than sodium. Does that mean the formula of salt is Na₁₃Cl₁₄? What happens to the difference as the cube gets much bigger?
Where could you add the next ball to your diamond piece? Is there ever a last one?
Why is a diamond model built in 3D more useful than a flat drawing?
Challenge Variation
Groups predict how many balls of each color a cube with 4 balls along each edge needs, then build or draw it to check.
3
Model Critique Gallery
20 minGroups of 3-4
Six model cards are posted around the room: drawings, photos of ball-and-stick models and screenshots of computer models. Some are correct and some have one error. Groups rotate, decide if each model matches its formula or description, and write a one-sentence fix for any error.
The Six Cards
A drawing of ammonia with one nitrogen and four hydrogen balls (error: one hydrogen too many).
A ball-and-stick photo of methanol with all six atoms joined correctly (correct).
A computer model of water that colors oxygen red and hydrogen white, with a key (correct).
A drawing of sodium chloride as a single pair, one sodium joined to one chlorine, labeled "a salt molecule" (error: salt is an extended structure; the pair is only the ratio).
A flat drawing of diamond as a straight chain of carbon atoms (error: diamond is a 3D network, and each carbon is joined to 4 others).
A computer model of carbon dioxide with the carbon at one end and both oxygens on the other side (error: the carbon is in the middle, joined to an oxygen on each side).
Discussion Questions
Four cards have an error. Which of them are wrong because of the number of atoms, and which because of how the atoms are arranged?
Which kind of model, a drawing, a ball-and-stick model or a computer model, made each error easiest to spot?
Modification for Distance Learning
Post the six cards on a slide deck. Each student writes a fix for every card in the speaker notes and compares with a partner in a video call.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Ball-and-Stick Models of Ammonia and Methanol
Flat drawings of two simple molecules. Each ball is one atom and each stick shows two joined atoms. Ammonia has 4 atoms of 2 elements; methanol has 6 atoms of 3 elements. Ball sizes and colors are only a code: real atoms have no colors.
Diagram 2: One Layer of a Sodium Chloride (Salt) Model
A flat layer of a salt crystal model, with sodium and chlorine alternating. This piece has 12 of each, a 1 : 1 ratio. A real crystal repeats the pattern in every direction, which is why salt is an extended structure and its formula, NaCl, gives a ratio rather than a molecule.
04
Homework Assignment
~30 min
MS-PS1-1 Homework: Modeling Molecules and Extended Structures
Directions: For every model you draw, include a key that shows which color or letter stands for each element. Use dashed lines to show where an extended structure keeps going. Show how you counted.
Part 1: Simple Molecules (Problems 1-3)
Acetic acid gives vinegar its sour taste. Its formula is CH₃COOH. (a) List the elements in it. (b) How many atoms of each element are in one molecule? (c) What is the total number of atoms? (d) Draw a ball-and-stick model with a key.
Rubbing alcohol is mostly isopropyl alcohol, C₃H₇OH. (a) How many atoms of each element and how many atoms in all are in one molecule? (b) You want to build 2 molecules. A kit has 10 carbon, 14 hydrogen and 6 oxygen balls. Is the kit enough? If not, which balls run out, and by how many?
Ethane (C₂H₆) and ethylene (C₂H₄) are two gases made of the same two elements. (a) Count the atoms in one molecule of each. (b) A classmate says, "They have the same elements, so they must be the same substance." Use your counts to explain why the classmate is wrong.
Part 2: Extended Structures (Problems 4-6)
Silicon carbide is the hard grit on some sandpaper. A model of one flat layer is a 4 × 4 square of balls, with silicon and carbon alternating like the squares on a checkerboard. (a) How many balls of each kind are in the layer? (b) What is the ratio, and what formula does it suggest? (c) Explain why silicon carbide is called an extended structure and not a molecule.
Fluorite is a mineral made of calcium and fluorine. A model piece of fluorite has 4 calcium balls and 8 fluorine balls. (a) What is the ratio of calcium to fluorine? (b) Write the formula. (c) A bigger model piece has 32 calcium balls. How many fluorine balls does it need?
A student claims: "All solids are extended structures, and all molecules are gases or liquids." Ice is solid water, H₂O, and a diamond is solid carbon. Use what each is made of to write a claim, evidence and reasoning response. In your answer, sketch a model of a tiny piece of each solid.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Reading Formulas
Correct atoms of each element and total for every formula, with the counting shown
One counting error, such as a missed subscript or a missed letter
Models
Every model has a key, the right number of balls of each kind, and dashed lines for extended structures
Model has the right atoms but is missing a key or the continuing pattern
Explaining Structures
Uses the model to explain the difference between a molecule (fixed number of atoms) and an extended structure (repeating ratio)
Names the correct type without a reason from the model
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Read each formula carefully: a subscript tells how many atoms of the element just before it, and no subscript means 1. 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
Which statement best describes a molecule?
Answer: B
A molecule is a small group of atoms joined together, and every molecule of a substance has the same atoms. Choice D describes an extended structure instead. Choice C leaves out the joining: a molecule has at least two atoms. Choice A describes a sample of matter, which is made of a huge number of particles.
Question 2 of 20 · Multiple Choice
Ethanol, the alcohol in hand sanitizer, has the formula C₂H₅OH. How many atoms are in one molecule of ethanol?
Answer: D
C₂ is 2 carbon, H₅ is 5 hydrogen, O is 1 oxygen and the last H is 1 more hydrogen: 2 + 5 + 1 + 1 = 9 atoms. Choice A counts the 3 elements instead of the atoms. Choice B forgets the last H. Choice C multiplies the subscripts 2 × 5 instead of adding the atoms.
Question 3 of 20 · Multiple Choice
Ozone, a gas high in the atmosphere, has the formula O₃. Which ball-and-stick model matches it?
Answer: C
O₃ means 3 oxygen atoms, and a molecule is a joined group, so the model has three joined oxygen balls (a bent shape). Choice A treats the subscript as a label instead of a count. Choice B adds hydrogen, which is not in the formula. Choice D shows three separate atoms, not one molecule.
Question 4 of 20 · Multiple Choice
Which of these is an extended structure?
Answer: A
Copper metal is a huge repeating pattern of copper atoms with no set size, so it is an extended structure. Water vapor, carbon dioxide and ammonia are made of separate small molecules (3, 3 and 4 atoms), so choices B, C and D are simple molecules.
Question 5 of 20 · Multiple Choice
Corundum, the hard mineral in rubies, is an extended structure of aluminum (Al) and oxygen (O). A model of a small piece has 20 aluminum balls and 30 oxygen balls, and the pattern continues past the edges. Which formula fits?
Answer: B
20 : 30 simplifies to 2 : 3, so there are 2 aluminum for every 3 oxygen and the formula is Al₂O₃. Choice C writes the counts of this one piece, but a bigger piece would give bigger numbers: the formula of an extended structure shows only the ratio. Choice A ignores the ratio, and choice D turns it upside down.
Question 6 of 20 · Multiple Choice
The mineral zinc blende is an extended structure of zinc (Zn) and sulfur (S). Why is its formula written ZnS instead of a count such as Zn₅₀₀S₅₀₀?
Answer: C
Zinc blende is an extended structure. Any piece has many zinc and sulfur particles in a 1 : 1 ratio, and a bigger piece has more of both, so the formula gives only the ratio. Choice B treats it as a simple molecule, and choice A contradicts the formula, whose Zn stands for zinc.
Question 7 of 20 · Multiple Choice
Propane, a grill fuel, has the formula C₃H₈. A student's model has 3 carbon balls and 6 hydrogen balls. What change makes the model match the formula?
Answer: A
H₈ means 8 hydrogen atoms, and the model has 6, so it needs 8 - 6 = 2 more. Choice C adds 8 on top of the 6 already there, giving 14. Choice B changes the carbon, which is already right at 3. Choice D adds an element that is not in the formula.
Question 8 of 20 · Multiple Choice
Pure silicon, used to make computer chips, is an extended structure. Its formula is written simply as Si. What does this tell you?
Answer: A
The formula Si names only one element, so pure silicon is made only of silicon atoms, joined in a network with no set size. Choice B reads the formula as one atom, but even a tiny chip has an enormous number. Choice D adds oxygen, which the formula does not show.
Question 9 of 20 · Multiple Choice
Titanium dioxide, the white color in many paints, is an extended structure with 2 oxygen atoms for every titanium atom. A model piece has 8 titanium balls. How many oxygen balls does it need?
Answer: C
The ratio is 1 titanium : 2 oxygen, so 8 titanium need 8 × 2 = 16 oxygen. Choice B uses a 1 : 1 ratio. Choice A turns the ratio around (8 ÷ 2). Choice D adds 2 instead of multiplying by 2.
Question 10 of 20 · Multiple Choice
Which kind of model best shows how the atoms in a molecule are arranged in three dimensions?
Answer: C
A 3D ball-and-stick model shows which atoms are joined and the shape they make, and you can look at it from any side. A formula (choice A) and a list of elements (choice D) tell what atoms are present but not where they are. A name (choice B) gives no arrangement at all.
Question 11 of 20 · Multiple Choice
A class looks at the same molecule as a clay model and as a computer model. Which is a real advantage of the computer model?
Answer: B
A computer model can be turned, zoomed and colored by element instantly, which helps compare molecules. Choice A is a misconception: atoms have no colors, and the colors in every model are only a code. Choices C and D confuse the model with the real thing.
Question 12 of 20 · Multiple Choice
A pair builds 2 water molecules (H₂O) and 1 carbon dioxide molecule (CO₂). How many oxygen balls do they use in all?
Answer: D
Each water molecule has 1 oxygen, so 2 waters use 2, and carbon dioxide has 2 oxygen: 2 + 2 = 4. Choice A counts only the water. Choice B uses one oxygen per molecule. Choice C is the total of all the balls: 4 hydrogen, 4 oxygen and 1 carbon.
Question 13 of 20 · Multiple Choice
Table sugar is a crystal, and its formula is C₁₂H₂₂O₁₁. Which statement is supported by the formula?
Answer: B
The subscripts give a fixed count: 12 + 22 + 11 = 45 atoms of carbon, hydrogen and oxygen in every molecule. A sugar crystal is many of these molecules stacked together, so choice A is a common mix-up: being a crystal does not make a substance an extended structure. Choice C counts the elements, not the atoms.
Question 14 of 20 · Multiple Choice
In a model layer of a mystery mineral, every row has the same repeating pattern: one gray ball, then two white balls, then one gray, two white, and so on. What is the ratio of gray to white?
Answer: D
Each repeat of the pattern has 1 gray and 2 white balls, so the ratio is 1 : 2. Choice B turns it around. Choice C counts all three balls in a repeat as white. Choice A would need the colors to alternate one by one.
Question 15 of 20 · Short Answer
Hydrogen peroxide (H₂O₂) is sold in drugstores to clean cuts. In one molecule, the two oxygen atoms are joined to each other, and each oxygen is also joined to one hydrogen. Describe or draw a ball-and-stick model, and give the total number of atoms.
A chain of four balls: H joined to O, that O joined to the second O, and the second O joined to the second H (H-O-O-H). There are 2 hydrogen and 2 oxygen atoms, 4 atoms in all. A full answer includes a key (for example, white = hydrogen, red = oxygen).
Question 16 of 20 · Short Answer
Sort each substance as a simple molecule or an extended structure, and give one reason for each: nitrogen gas (N₂), aluminum foil, glucose (C₆H₁₂O₆).
Nitrogen gas: simple molecule, each molecule has exactly 2 nitrogen atoms. Aluminum foil: extended structure, a repeating pattern of aluminum atoms with no set size. Glucose: simple molecule, every molecule has the same fixed number of atoms given by the subscripts.
Question 17 of 20 · Short Answer
Glucose is a sugar your body uses for energy. Its formula is C₆H₁₂O₆. How many atoms of each element are in one molecule, and how many atoms in all?
6 carbon, 12 hydrogen and 6 oxygen atoms, so 6 + 12 + 6 = 24 atoms.
Question 18 of 20 · Short Answer
Magnesium oxide is an extended structure with a 1 : 1 ratio of magnesium to oxygen. A model of one flat layer is a 5 × 5 square of balls, alternating like a checkerboard with oxygen in the corners. How many balls of each kind are there? Why is the formula still MgO?
The layer has 25 balls: 13 oxygen and 12 magnesium (the corners and every other ball are oxygen). The formula is still MgO because the real crystal goes on far past this small piece, and over the whole crystal there is 1 magnesium for every 1 oxygen. The extra ball comes only from where the model was cut off.
Question 19 of 20 · Short Answer
A student says: "A diamond is one giant molecule of carbon, so its formula should be C with a huge number after it." Evaluate the claim using what a model of diamond shows.
The claim gets one thing right: all the carbon atoms in a diamond are joined into one connected piece. But a diamond has no set size: a bigger diamond has more carbon atoms in the same repeating pattern. Any number written in the formula would only describe one stone. So diamond is an extended structure, and its formula is written C, the element in the pattern.
Question 20 of 20 · Short Answer
Name one strength and one limitation of a flat drawing of a molecule and of a 3D ball-and-stick model of the same molecule.
Sample answer. Drawing: it is quick to make and easy to label and share, but it is flat, so it cannot show the real 3D shape. Ball-and-stick model: it shows the 3D shape and which atoms are joined, and you can turn it, but the balls and sticks are far too big, the colors are not real, and real atoms are not held apart by sticks. Accept any accurate strength and limitation for each.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-PS1-1 mean?
MS-PS1-1 asks students to develop models that show what atoms make up simple molecules and extended structures. Students use drawings, ball-and-stick models and computer models to show which elements are present and how many atoms of each, for molecules such as ammonia and methanol and for repeating structures such as salt and diamond. The code means Middle School, Physical Science, core idea 1 (Matter and Its Interactions), performance expectation 1.
What grade is MS-PS1-1 taught in?
It is a middle school standard, so it can be taught in grade 6, 7 or 8. Schools decide the order: some teach the chemistry standards in grade 7 or 8, and some spread them over a three-year physical science sequence. Students only need to read simple formulas and compare small ratios.
What is the assessment boundary for MS-PS1-1?
Assessment does not include valence electrons, bonding energy or the ionic nature of the particles in structures like salt, and students do not need to describe every atom in a complex molecule or structure. In short, students model which atoms are present and how they are arranged, without explaining why atoms join. Those ideas come in high school chemistry.
What is the difference between a simple molecule and an extended structure?
A simple molecule has a fixed, countable number of atoms, and every molecule of that substance is the same. An extended structure is a pattern of joined atoms that repeats in every direction with no set size, so its formula gives a ratio instead of a count. Water and ammonia are molecules; table salt and diamond are extended structures.
Is a crystal always an extended structure?
No. Some crystals are made of separate molecules stacked in a neat, repeating pattern. The test is in the model: if you can circle identical small groups of atoms that are not joined to each other, the crystal is made of molecules. Salt and diamond crystals are extended structures because the atoms themselves are joined in one repeating network.
What kinds of models can students use for MS-PS1-1?
The Clarification Statement names drawings, 3D ball-and-stick structures and computer representations. In class, these can be sketches with a color key, clay balls and toothpicks, foam balls and pipe cleaners, a commercial model kit, or a free online molecule viewer that lets students rotate a model. Using more than one kind helps students see what each model shows and what it leaves out.
Do students need to know about electrons or bonds for MS-PS1-1?
No. The Assessment Boundary leaves out valence electrons and bonding energy. In models on this page, a stick only shows that two atoms are joined. Why atoms join, and how many joins each kind of atom makes, are high school topics.
Are the colors in a molecule model the real colors of atoms?
No. Atoms are far too small to have a color you could see. Model makers choose colors as a code, for example black for carbon, white for hydrogen, red for oxygen and blue for nitrogen, so every model needs a key. This is a common misconception worth asking about directly.
How do I check a student's molecule model quickly?
Count balls of each color and compare with the formula's subscripts, check that a key is present, and check that the atoms in a molecule are all joined into one unit. For an extended structure, check the ratio of the two kinds of balls and look for a sign that the pattern continues, such as dashed lines or a written note.
How does MS-PS1-1 connect to high school chemistry?
In high school, HS-PS1-1 uses the periodic table and outer electrons to explain why atoms join the way they do, and HS-PS1-3 links the kind of structure to properties such as melting point. Middle school models of molecules and extended structures give students the picture of matter those standards build on. Within middle school, MS-PS1-5 uses the same models to show that atoms are rearranged, not lost, in chemical reactions.
07
Related Standards
5 standards
These standards connect to MS-PS1-1: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
5-PS1-1Prerequisite
Model that matter is made of particles too small to be seen
Lesson coming soon
Alongside
MS-PS1-4Parallel
Model how particle motion, temperature and state change when thermal energy changes
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