Next Generation Science Standards

Performance Expectation

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.

Just like every part of a car works together to make the whole thing go, this performance expectation is about seeing that what happens on a big scale is a result of things on a tiny scale. Think of it like this: in civics class, we learned how everyone voting determines what issues our Congress and president address. (Well, that's the idea, at least.) In science, the ‘votes’ of the molecules determine the characteristics of the material. A single molecule of steel embedded in a bunch of rubber molecules will have its preference for ‘strong and rigid’ outvoted by the ‘flexible and stretchy’ faction.

Not only should students understand why metals conduct, rubber bends, and drugs work. They should also be able to communicate those "whys" to others. That communication might be nothing more than drawing diagrams and explaining them to the class. However, there are lots of ways to achieve this.

Here are a couple activity ideas to help students get the word out:

• Play a game of air-hockey. After all, the air-hockey puck is floating on a layer of air in the same way that we never really touch the ground.
• Saran-wrap sensing. Have your students perform intricate tasks with their fingers covered tightly with plastic wrap. Is it harder? Maybe a little. However, the key point here is that they don't need to touch something to feel a force.
• There are definitely enough examples of this performance expectation to form a decent research project. One student can research how molecular forces create friction; another, the normal force; a third student can explain why metals are conductors; while student #4 looks into why polymers are flexible. All of these topics will help them connect the very tiny to the everyday scale they're used to. Then have students present their research to the class: that's the scientific and technical communication part. What would research be without a good poster presentation? (Nothing, that's what.)
• Explaining how stuff on the molecular-level affects the larger scale is hard to do without diagrams; so why not take it to the nth-degree? Have them draw a comic strip explaining a substance you assign. Then you'll have some great material to hang on your wall. Extra bonus points for every nerdy reference they use.

Disciplinary Core Ideas

PS1.A – Structure and Properties of Matter: The structure and interactions of matter at the bulk scale are determined by electrical forces within and between atoms. (Secondary to HS-PS2-6)

Material characteristics aren't the only things determined by molecular voting. The material’s structure is also determined by the shape of the molecules and how they fit together. Many molecules are unusual shapes, with tetrahedral being a popular choice. Imagine trying to build with tetrahedral legos—it makes us cry. Putting a cubical block in with 4 tetrahedral blocks will make a different shape than 5 tetrahedral blocks, and thus give the materials different properties. The shape of the molecule is, in turn, determined by the electrical properties of the atoms that make it up. How full is that outer shell of electrons for each atom involved? Students need to understand these ideas.

How this material interacts with other materials is also dependant on the electrical properties of the molecule. The bonding of atoms together as molecules is dependent on the electrical arrangement of the electrons. These same electrical arrangements determine if differing molecules interact. When a carbon molecule meets two oxygen molecules, the electrical properties say that they will combine to make 2 carbon dioxide molecules. The difficulty in breaking up a molecule is determined by its electrical structure as well. Students should understand that every characteristic of a material, including how it interacts with other molecules, is ultimately governed by the electrical properties of the atoms involved.

PS2.B –Types of Interactions: Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects.

Time for students to take the red pill and go all the way down the rabbit hole. The idea that you never really touch things is hard to accept. We touch things all the time. However, when your students realize that what feels like their pencil is actually the electric repulsion between the atoms of the pencil and their hand, the world will never quite look the same again.

Why is a solid a solid? What about liquids, gases, and plasmas—what makes them what they are? When we talk about forces, we often ignore the “why” part. There's this force of friction between two surfaces. It's mechanics, but it's also electrostatics—there would be no friction without molecular electrostatic forces.

We can legitimately tell the kids they can levitate. Point your wand and say, “Wingardium leviosa!” because they're floating over the floor, lifted by the electrostatic forces between the molecules. Nobody ever really touches a surface at all.

Key areas for students to understand for this disciplinary core idea include how the low level of attraction between electrons and metal atoms causes materials to be conductive, how the electric forces inside long-chain molecules cause polymers to be flexible, and how charged drugs interact with the electric field of receptors in the body. Anything where the molecular level causes bulk properties will help meet this performance standard.

Students always learn better when they see things for themselves. Unfortunately students can't see molecules, so teaching this will involve diagrams, diagrams, and more diagrams. Thanks to electron microscopes, you might be able to find some useful images online, but there's nothing quite like painting a picture to...paint a picture.

Science and Engineering Practices

Obtaining, Evaluating, and Communicating Information: Communicate scientific and technical information (e.g., about the process of development and the design and performance of a proposed process or system) in multiple formats (including oral, graphical, textual and mathematical).

It doesn’t matter what you know if you can’t clearly communicate it. Real, technical communication. Txt spk won't cut it. Not only do your students need to know about how electric repulsion affects materials on a large scale, they also need to communicate that information scientifically. Whether this is an oral presentation, a poster, or an essay, the key is that they found the information themselves, evaluated it, and found a way to clearly and explicitly communicate their results to their classmates.

Crosscutting Concepts

Structure and Function: Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem.

A rubber-band made of cast iron wouldn't be very functional. There's a reason things are made out of what they are, and it goes all the way down to the molecular level. Stretchy materials get stretchy jobs. Rigid materials hold our buildings upright, and hard materials keep our old Nokia from breaking.

The function of a material is related to its structure, and in many cases related to the electric forces between atoms and molecules. This cross-cutting concept simply requires students to appreciate that connection between structure and function.