Students who demonstrate understanding can: 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.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
Everything around us is built from a little over a hundred kinds of atoms, combined in different ways. Middle schoolers learn to draw or build models that show which atoms make up a substance and how many of each there are. A water molecule is one oxygen atom joined to two hydrogen atoms; ammonia is one nitrogen with three hydrogens; methanol has one carbon, one oxygen and four hydrogens.
Not every substance comes in small, separate molecules. Table salt and diamond are extended structures: a repeating pattern of atoms (or, for salt, charged particles) that continues in every direction for as long as the crystal lasts. A grain of salt has no single 'salt molecule' inside it, just a huge lattice where sodium and chlorine alternate in a fixed ratio of one to one.
Students should be able to compare these two kinds of models, using ball-and-stick drawings, space-filling sketches or digital models, and explain what each part of the model represents. Explaining bonding energy or valence electrons is beyond the scope at this level.
Students may think a single copper atom is orange or a single water molecule is wet. Properties like color and wetness belong to huge numbers of particles together, not to one particle.
Many students assume salt and diamond have small molecules like water. Show a lattice model and ask where one molecule would start and end; the pattern simply keeps repeating.
Ball-and-stick models use sticks to show which atoms are joined. Point out that atoms are not connected by rods, and compare with a space-filling model where atoms overlap.
Knowing that ammonia is NH3 does not tell you how the atoms are arranged in space. The model adds information the formula alone cannot show.
A student builds a model of methanol and a model of a sodium chloride crystal. Describe what each model should show and one key difference between them.
Answer: Methanol is a simple molecule with a fixed count of 6 atoms; sodium chloride is an extended structure, a repeating lattice with a 1 to 1 ratio of sodium to chlorine and no single molecule.
Give students a bag of colored modeling clay or snap-together atoms and a short list of formulas. After they build water, ammonia and methanol, hand out a photo of a salt crystal and ask them to build 'one piece' of salt. The struggle to decide where the piece ends is the lesson.
Assessment items often show a ball-and-stick picture with a key and ask students to name or count the atoms, or to sort pictures into molecules versus extended structures. Practice reading keys carefully, since colors are not standardized across tests.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: B) 4
One nitrogen plus three hydrogens makes 4 atoms. This is a model of ammonia.
Answer: C) Diamond
Diamond is a continuous network of carbon atoms that repeats in every direction. Water, ammonia and methanol are made of separate small molecules.
Answer: D) 1 to 1
Sodium and chlorine alternate in the lattice, so there is always one sodium for every chlorine, no matter how large the crystal is.
Answer: A) So readers know which ball stands for which kind of atom
Atoms do not have colors. The key is a convention that tells the reader which element each ball represents.
Answer: structure (also accepted: extended structure)
Extended structures, such as salt and diamond, are repeating lattices of atoms rather than collections of separate molecules.
Answer: C) Wetness is a property of many molecules together, not one molecule
Properties such as wetness, color and hardness come from the behavior of enormous numbers of particles together. A single molecule does not have them.
Answer: 4 (also accepted: four)
Methanol has three hydrogens on the carbon and one on the oxygen, making 4 hydrogen atoms.
Develop a model to describe that matter is made of particles too small to be seen.
A full lesson with slides, activities and an exit ticket on modeling atoms in molecules, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on MS-PS1-1 with an answer key, ready in about a minute.
Make a worksheet βTurn modeling atoms in molecules into a quiz students answer online that marks itself, with a class summary for you.
Build a test βStudents build or draw models showing which atoms make up simple molecules, such as ammonia, and extended structures, such as salt or diamond, and explain how the two kinds of models differ.
No. The assessment boundary leaves out valence electrons, bond energies and the ionic nature of structures. The focus is on what atoms are present and how they are arranged.